• CBOR has capabilities that are not present in JSON and are appropriate to use. One example of this is the fact that CBOR has a method of encoding binary data directly without first converting it into a base64-encoded text string.
• COSE is not a direct copy of the JOSE specification. In the process of creating COSE, decisions that were made for JOSE were re-examined. In many cases, different results were decided on, as the criteria were not always the same.

• The description of the structure for the CBOR objects that are transmitted over the wire. Two objects each are defined for encryption, signing, and message authentication. One object is defined for transporting keys and one for transporting groups of keys.
• The procedures used to build the inputs to the cryptographic functions required for each of the structures.
• A set of attributes that apply to the different security objects.

• Split the original document into this document and [RFC 9053].
• Added some text describing why there is no digest structure defined by COSE.
• Made text clarifications and changes in terminology.
• Removed all of the details relating to countersignatures and placed them in [COSE-COUNTERSIGN].

• A single overall message structure has been defined so that encrypted, signed, and MACed messages can easily be identified and still have a consistent view.
• Signed messages distinguish between the protected and unprotected header parameters that relate to the content and those that relate to the signature.
• MACed messages are separated from signed messages.
• MACed messages have the ability to use the same set of recipient algorithms as enveloped messages for obtaining the MAC authentication key.
• Binary encodings are used, rather than base64url encodings, to encode binary data.
• The authentication tag for encryption algorithms has been combined with the ciphertext.
• The set of cryptographic algorithms has been expanded in some directions and trimmed in others.

any:

A nonspecific value that permits all CBOR values to be placed here.

bool:

A boolean value (true: major type 7, value 21; false: major type 7, value 20).

bstr:

Byte string (major type 2).

int:

An unsigned integer or a negative integer.

nil:

A null value (major type 7, value 22).

nint:

A negative integer (major type 1).

tstr:

A UTF-8 text string (major type 3).

uint:

An unsigned integer (major type 0).

FOO / BAR:

Indicates that either FOO or BAR can appear here.

[+ FOO]:

Indicates that the type FOO appears one or more times in an array.

* FOO:

Indicates that the type FOO appears zero or more times.

type1 .cbor type2:

Indicates that the contents of type1, usually bstr, contains a value of type2.

type1 .size integer:

Indicates that the contents of type1 is integer bytes long.

//sourcecode[@type='cddl']/text()

start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types

; This is defined to make the tool quieter:
Internal_Types = Sig_structure / Enc_structure / MAC_structure

Byte:

A synonym for octet.

Constrained Application Protocol (CoAP):

A specialized web transfer protocol for use in constrained systems. It is defined in [RFC 7252].

Encryption algorithms that provide an authentication check of the contents along with the encryption service. An example of an AE algorithm used in COSE is AES Key Wrap [RFC 3394]. These algorithms are used for key encryption, but Authenticated Encryption with Associated Data (AEAD) algorithms would be preferred.

Encryption algorithms that provide the same authentication service of the content as AE algorithms do, and also allow associated data that is not part of the encrypted body to be included in the authentication service. An example of an AEAD algorithm used in COSE is AES-GCM [RFC 5116]. These algorithms are used for content encryption and can be used for key encryption as well.

1. The protected header parameters, encoded and wrapped in a bstr.
2. The unprotected header parameters as a map.
3. The content of the message. The content is either the plaintext or the ciphertext, as appropriate. The content may be detached (i.e., transported separately from the COSE structure), but the location is still used. The content is wrapped in a bstr when present and is a nil value when detached.

1. The specific message type is known from the context. This may be defined by a marker in the containing structure or by restrictions specified by the application protocol.
2. The message type is identified by a CBOR tag. Messages with a CBOR tag are known in this specification as tagged messages, while those without the CBOR tag are known as untagged messages. This document defines a CBOR tag for each of the message structures. These tags can be found in Table 1.
3. When a COSE object is carried in a media type of "application/cose", the optional parameter "cose-type" can be used to identify the embedded object. The parameter is OPTIONAL if the tagged version of the structure is used. The parameter is REQUIRED if the untagged version of the structure is used. The value to use with the parameter for each of the structures can be found in Table 1.
4. When a COSE object is carried as a CoAP payload, the CoAP Content-Format Option can be used to identify the message content. The CoAP Content-Format values can be found in Table 2. The CBOR tag for the message structure is not required, as each security message is uniquely identified.

COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message

COSE_Untagged_Message = COSE_Sign / COSE_Sign1 /
    COSE_Encrypt / COSE_Encrypt0 /
    COSE_Mac / COSE_Mac0

COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged /
    COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged /
    COSE_Mac_Tagged / COSE_Mac0_Tagged

protected:

Contains parameters about the current layer that are cryptographically protected. This bucket MUST be empty if it is not going to be included in a cryptographic computation. This bucket is encoded in the message as a binary object. This value is obtained by CBOR encoding the protected map and wrapping it in a bstr object. Senders SHOULD encode a zero-length map as a zero-length byte string rather than as a zero-length map (encoded as h'a0'). The zero-length byte string encoding is preferred, because it is both shorter and the version used in the serialization structures for cryptographic computation. Recipients MUST accept both a zero-length byte string and a zero-length map encoded in a byte string.

Wrapping the encoding with a byte string allows the protected map to be transported with a greater chance that it will not be altered accidentally in transit. (Badly behaved intermediates could decode and re-encode, but this will result in a failure to verify unless the re-encoded byte string is identical to the decoded byte string.) This avoids the problem of all parties needing to be able to do a common canonical encoding of the map for input to cryptographic operations.

unprotected:

Contains parameters about the current layer that are not cryptographically protected.

Headers = (
    protected : empty_or_serialized_map,
    unprotected : header_map
)

header_map = {
    Generic_Headers,
    * label => values
}

empty_or_serialized_map = bstr .cbor header_map / bstr .size 0

alg:

This header parameter is used to indicate the algorithm used for the security processing. This header parameter MUST be authenticated where the ability to do so exists. This support is provided by AEAD algorithms or construction (e.g., COSE_Sign and COSE_Mac0). This authentication can be done either by placing the header parameter in the protected-header-parameters bucket or as part of the externally supplied data (Section 4.3). The value is taken from the "COSE Algorithms" registry (see [COSE.Algorithms]).

crit:

This header parameter is used to indicate which protected header parameters an application that is processing a message is required to understand. Header parameters defined in this document do not need to be included, as they should be understood by all implementations. Additionally, the header parameter "counter signature" (label 7) defined by [RFC 8152] must be understood by new implementations, to remain compatible with senders that adhere to that document and assume all implementations will understand it. When present, the "crit" header parameter MUST be placed in the protected-header-parameters bucket. The array MUST have at least one value in it.

Not all header-parameter labels need to be included in the "crit" header parameter. The rules for deciding which header parameters are placed in the array are:

• Integer labels in the range of 0 to 7 SHOULD be omitted.
• Integer labels in the range -1 to -128 can be omitted. Algorithms can assign labels in this range where the ability to process the content of the label is considered to be core to implementing the algorithm. Algorithms can assign labels outside of this range and include them in the "crit" header parameter when the ability to process the content of the label is not considered to be core functionality of the algorithm but does need to be understood to correctly process this instance. Integer labels in the range -129 to -65536 SHOULD be included, as these would be less common header parameters that might not be generally supported.
• Labels for header parameters required for an application MAY be omitted. Applications should have a statement declaring whether or not the label can be omitted.

The header parameters indicated by "crit" can be processed by either the security-library code or an application using a security library; the only requirement is that the header parameter is processed. If the "crit" value list includes a label for which the header parameter is not in the protected-header-parameters bucket, this is a fatal error in processing the message.

content type:

This header parameter is used to indicate the content type of the data in the "payload" or "ciphertext" field. Integers are from the "CoAP Content-Formats" IANA registry table [COAP.Formats]. Text values follow the syntax of "<type-name>/<subtype-name>", where <type-name> and <subtype-name> are defined in Section 4.2 of RFC 6838. Leading and trailing whitespace is not permitted. Textual content type values, along with parameters and subparameters, can be located using the IANA "Media Types" registry. Applications SHOULD provide this header parameter if the content structure is potentially ambiguous.

kid:

This header parameter identifies one piece of data that can be used as input to find the needed cryptographic key. The value of this header parameter can be matched against the "kid" member in a COSE_Key structure. Other methods of key distribution can define an equivalent field to be matched. Applications MUST NOT assume that "kid" values are unique. There may be more than one key with the same "kid" value, so all of the keys associated with this "kid" may need to be checked. The internal structure of "kid" values is not defined and cannot be relied on by applications. Key identifier values are hints about which key to use. This is not a security-critical field. For this reason, it can be placed in the unprotected-header-parameters bucket.

IV:

This header parameter holds the Initialization Vector (IV) value. For some symmetric encryption algorithms, this may be referred to as a nonce. The IV can be placed in the unprotected bucket, since for AE and AEAD algorithms, modifying the IV will cause the decryption to fail.

Partial IV:

This header parameter holds a part of the IV value. When using the COSE_Encrypt0 structure, a portion of the IV can be part of the context associated with the key (Context IV), while a portion can be changed with each message (Partial IV). This field is used to carry a value that causes the IV to be changed for each message. The Partial IV can be placed in the unprotected bucket, as modifying the value will cause the decryption to yield plaintext that is readily detectable as garbled. The "Initialization Vector" and "Partial Initialization Vector" header parameters MUST NOT both be present in the same security layer.

The message IV is generated by the following steps:

1. Left-pad the Partial IV with zeros to the length of IV (determined by the algorithm).
2. XOR the padded Partial IV with the Context IV.

Generic_Headers = (
    ? 1 => int / tstr,  ; algorithm identifier
    ? 2 => [+label],    ; criticality
    ? 3 => tstr / int,  ; content type
    ? 4 => bstr,        ; key identifier
    ? ( 5 => bstr //    ; IV
        6 => bstr )     ; Partial IV
)

COSE_Sign_Tagged = #6.98(COSE_Sign)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

payload:

This field contains the serialized content to be signed. If the payload is not present in the message, the application is required to supply the payload separately. The payload is wrapped in a bstr to ensure that it is transported without changes. If the payload is transported separately ("detached content"), then a nil CBOR object is placed in this location, and it is the responsibility of the application to ensure that it will be transported without changes.

Note: When a signature with a message recovery algorithm is used (Section 8.1), the maximum number of bytes that can be recovered is the length of the original payload. The size of the encoded payload is reduced by the number of bytes that will be recovered. If all of the bytes of the original payload are consumed, then the transmitted payload is encoded as a zero-length byte string rather than as being absent.

signatures:

This field is an array of signatures. Each signature is represented as a COSE_Signature structure.

COSE_Sign = [
    Headers,
    payload : bstr / nil,
    signatures : [+ COSE_Signature]
]

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

signature:

This field contains the computed signature value. The type of the field is a bstr. Algorithms MUST specify padding if the signature value is not a multiple of 8 bits.

COSE_Signature =  [
    Headers,
    signature : bstr
]

COSE_Sign1_Tagged = #6.18(COSE_Sign1)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

payload:

This is as described in Section 4.1.

signature:

This field contains the computed signature value. The type of the field is a bstr.

COSE_Sign1 = [
    Headers,
    payload : bstr / nil,
    signature : bstr
]

• If multiple items are included, applications need to ensure that the same byte string cannot be produced if there are different inputs. An example of how the problematic scenario could arise would be by concatenating the text strings "AB" and "CDE" or by concatenating the text strings "ABC" and "DE". This is usually addressed by making fields a fixed width and/or encoding the length of the field as part of the output. Using options from CoAP [RFC 7252] as an example, these fields use a TLV structure so they can be concatenated without any problems.
• If multiple items are included, an order for the items needs to be defined. Using options from CoAP as an example, an application could state that the fields are to be ordered by the option number.
• Applications need to ensure that the byte string is going to be the same on both sides. Using options from CoAP might give a problem if the same relative numbering is kept. An intermediate node could insert or remove an option, changing how the relative numbering is done. An application would need to specify that the relative number must be re-encoded to be relative only to the options that are in the external data.

1. A context text string identifying the context of the signature. The context text string is:
   • "Signature" for signatures using the COSE_Signature structure.
   • "Signature1" for signatures using the COSE_Sign1 structure.
2. The protected attributes from the body structure, encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used.
3. The protected attributes from the signer structure, encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used. This field is omitted for the COSE_Sign1 signature structure.
4. The externally supplied data from the application, encoded in a bstr type. If this field is not supplied, it defaults to a zero-length byte string. (See Section 4.3 for application guidance on constructing this field.)
5. The payload to be signed, encoded in a bstr type. The full payload is used here, independent of how it is transported.

Sig_structure = [
    context : "Signature" / "Signature1",
    body_protected : empty_or_serialized_map,
    ? sign_protected : empty_or_serialized_map,
    external_aad : bstr,
    payload : bstr
]

1. Create a Sig_structure and populate it with the appropriate fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a byte string, using the encoding described in Section 9.
3. Call the signature creation algorithm, passing in K (the key to sign with), alg (the algorithm to sign with), and ToBeSigned (the value to sign).
4. Place the resulting signature value in the correct location. This is the "signature" field of the COSE_Signature or COSE_Sign1 structure.

1. Create a Sig_structure and populate it with the appropriate fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a byte string, using the encoding described in Section 9.
3. Call the signature verification algorithm, passing in K (the key to verify with), alg (the algorithm used to sign with), ToBeSigned (the value to sign), and sig (the signature to be verified).

COSE_Encrypt_Tagged = #6.96(COSE_Encrypt)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

ciphertext:

This field contains the ciphertext, encoded as a bstr. If the ciphertext is to be transported independently of the control information about the encryption process (i.e., detached content), then the field is encoded as a nil value.

recipients:

This field contains an array of recipient information structures. The type for the recipient information structure is a COSE_recipient.

COSE_Encrypt = [
    Headers,
    ciphertext : bstr / nil,
    recipients : [+COSE_recipient]
]

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

ciphertext:

This field contains the encrypted key, encoded as a bstr. All encoded keys are symmetric keys; the binary value of the key is the content. If there is not an encrypted key, then this field is encoded as a nil value.

recipients:

This field contains an array of recipient information structures. The type for the recipient information structure is a COSE_recipient (an example of this can be found in Appendix B). If there are no recipient information structures, this element is absent.

COSE_recipient = [
    Headers,
    ciphertext : bstr / nil,
    ? recipients : [+COSE_recipient]
]

direct:

The CEK is the same as the identified previously distributed symmetric key or is derived from a previously distributed secret. No CEK is transported in the message.

symmetric key-encryption keys (KEKs):

The CEK is encrypted using a previously distributed symmetric KEK. Also known as key wrap.

key agreement:

The recipient's public key and a sender's private key are used to generate a pairwise secret, a Key Derivation Function (KDF) is applied to derive a key, and then the CEK is either the derived key or encrypted by the derived key.

key transport:

The CEK is encrypted with the recipient's public key.

passwords:

The CEK is encrypted in a KEK that is derived from a password. As of when this document was published, no password algorithms have been defined.

COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

ciphertext:

This is as described in Section 5.1.

COSE_Encrypt0 = [
    Headers,
    ciphertext : bstr / nil,
]

1. A context text string identifying the context of the authenticated data structure. The context text string is:
   • "Encrypt0" for the content encryption of a COSE_Encrypt0 data structure.
   • "Encrypt" for the first layer of a COSE_Encrypt data structure (i.e., for content encryption).
   • "Enc_Recipient" for a recipient encoding to be placed in a COSE_Encrypt data structure.
   • "Mac_Recipient" for a recipient encoding to be placed in a MACed message structure.
   • "Rec_Recipient" for a recipient encoding to be placed in a recipient structure.
2. The protected attributes from the body structure, encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used.
3. The externally supplied data from the application encoded in a bstr type. If this field is not supplied, it defaults to a zero-length byte string. (See Section 4.3 for application guidance on constructing this field.)

Enc_structure = [
    context : "Encrypt" / "Encrypt0" / "Enc_Recipient" /
        "Mac_Recipient" / "Rec_Recipient",
    protected : empty_or_serialized_map,
    external_aad : bstr
]

1. Create an Enc_structure and populate it with the appropriate fields.
2. Encode the Enc_structure to a byte string (Additional Authenticated Data (AAD)), using the encoding described in Section 9.
3. Determine the encryption key (K). This step is dependent on the class of recipient algorithm being used. For:

   No Recipients:

   The key to be used is determined by the algorithm and key at the current layer. Examples are key wrap keys (Section 8.5.2) and preshared secrets.

   Direct Encryption and Direct Key Agreement:

   The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.) Examples of these algorithms are found in Sections 6.1 and 6.3 of [RFC 9053].

   Other:

   The key is randomly generated.
4. Call the encryption algorithm with K (the encryption key), P (the plaintext), and AAD. Place the returned ciphertext into the "ciphertext" field of the structure.
5. For recipients of the message using non-direct algorithms, recursively perform the encryption algorithm for that recipient, using K (the encryption key) as the plaintext.

1. Create an Enc_structure and populate it with the appropriate fields.
2. Encode the Enc_structure to a byte string (AAD), using the encoding described in Section 9.
3. Determine the decryption key. This step is dependent on the class of recipient algorithm being used. For:

   No Recipients:

   The key to be used is determined by the algorithm and key at the current layer. Examples are key wrap keys (Section 8.5.2) and preshared secrets.

   Direct Encryption and Direct Key Agreement:

   The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.)

   Other:

   The key is determined by decoding and decrypting one of the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use), C (the ciphertext), and AAD.

1. Verify that the "protected" field is a zero-length byte string.
2. Verify that there was no external additional authenticated data supplied for this operation.
3. Determine the encryption key. This step is dependent on the class of recipient algorithm being used. For:

   No Recipients:

   The key to be used is determined by the algorithm and key at the current layer. Examples are key wrap keys (Section 8.5.2) and preshared secrets.

   Direct Encryption and Direct Key Agreement:

   The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.)Examples of these algorithms are found in Sections 6.1 and 6.3 of [RFC 9053].

   Other:

   The key is randomly generated.
4. Call the encryption algorithm with K (the encryption key to use) and P (the plaintext). Place the returned ciphertext into the "ciphertext" field of the structure.
5. For recipients of the message using non-direct algorithms, recursively perform the encryption algorithm for that recipient, using K (the encryption key) as the plaintext.

1. Verify that the "protected" field is a zero-length byte string.
2. Verify that there was no external additional authenticated data supplied for this operation.
3. Determine the decryption key. This step is dependent on the class of recipient algorithm being used. For:

   No Recipients:

   The key to be used is determined by the algorithm and key at the current layer. Examples are key wrap keys (Section 8.5.2) and preshared secrets.

   Direct Encryption and Direct Key Agreement:

   The key is determined by the key and algorithm in the recipient structure. The encryption algorithm and size of the key to be used are inputs into the KDF used for the recipient. (For direct, the KDF can be thought of as the identity operation.)Examples of these algorithms are found in Sections 6.1 and 6.3 of [RFC 9053].

   Other:

   The key is determined by decoding and decrypting one of the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use) and C (the ciphertext).

COSE_Mac_Tagged = #6.97(COSE_Mac)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

payload:

This field contains the serialized content to be MACed. If the payload is not present in the message, the application is required to supply the payload separately. The payload is wrapped in a bstr to ensure that it is transported without changes. If the payload is transported separately (i.e., detached content), then a nil CBOR value is placed in this location, and it is the responsibility of the application to ensure that it will be transported without changes.

tag:

This field contains the MAC value.

recipients:

This is as described in Section 5.1.

COSE_Mac = [
   Headers,
   payload : bstr / nil,
   tag : bstr,
   recipients : [+COSE_recipient]
]

COSE_Mac0_Tagged = #6.17(COSE_Mac0)

protected:

This is as described in Section 3.

unprotected:

This is as described in Section 3.

payload:

This is as described in Section 6.1.

tag:

This field contains the MAC value.

COSE_Mac0 = [
   Headers,
   payload : bstr / nil,
   tag : bstr,
]

1. A context text string that identifies the structure that is being encoded. This context text string is "MAC" for the COSE_Mac structure. This context text string is "MAC0" for the COSE_Mac0 structure.
2. The protected attributes from the body structure. If there are no protected attributes, a zero-length bstr is used.
3. The externally supplied data from the application, encoded as a bstr type. If this field is not supplied, it defaults to a zero-length byte string. (See Section 4.3 for application guidance on constructing this field.)
4. The payload to be MACed, encoded in a bstr type. The full payload is used here, independent of how it is transported.

MAC_structure = [
     context : "MAC" / "MAC0",
     protected : empty_or_serialized_map,
     external_aad : bstr,
     payload : bstr
]

1. Create a MAC_structure and populate it with the appropriate fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a byte string, using the encoding described in Section 9.
3. Call the MAC creation algorithm, passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on).
4. Place the resulting MAC in the "tag" field of the COSE_Mac or COSE_Mac0 structure.
5. For COSE_Mac structures, encrypt and encode the MAC key for each recipient of the message.

1. Create a MAC_structure and populate it with the appropriate fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a byte string, using the encoding described in Section 9.
3. For COSE_Mac structures, obtain the cryptographic key by decoding and decrypting one of the recipient structures.
4. Call the MAC creation algorithm, passing in K (the key to use), alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on).
5. Compare the MAC value to the "tag" field of the COSE_Mac or COSE_Mac0 structure.

kty:

This parameter is used to identify the family of keys for this structure and, thus, the set of key-type-specific parameters to be found. The set of values defined in this document can be found in [COSE.KeyTypes]. This parameter MUST be present in a key object. Implementations MUST verify that the key type is appropriate for the algorithm being processed. The key type MUST be included as part of the trust-decision process.

alg:

This parameter is used to restrict the algorithm that is used with the key. If this parameter is present in the key structure, the application MUST verify that this algorithm matches the algorithm for which the key is being used. If the algorithms do not match, then this key object MUST NOT be used to perform the cryptographic operation. Note that the same key can be in a different key structure with a different or no algorithm specified; however, this is considered to be a poor security practice.

kid:

This parameter is used to give an identifier for a key. The identifier is not structured and can be anything from a user-provided byte string to a value computed on the public portion of the key. This field is intended for matching against a "kid" parameter in a message in order to filter down the set of keys that need to be checked. The value of the identifier is not a unique value and can occur in other key objects, even for different keys.

key_ops:

This parameter is defined to restrict the set of operations that a key is to be used for. The value of the field is an array of values from Table 5. Algorithms define the values of key ops that are permitted to appear and are required for specific operations. The set of values matches that in [RFC 7517] and [W3C.WebCrypto].

Base IV:

This parameter is defined to carry the base portion of an IV. It is designed to be used with the Partial IV header parameter defined in Section 3.1. This field provides the ability to associate a Base IV with a key that is then modified on a per-message basis with the Partial IV.

Extreme care needs to be taken when using a Base IV in an application. Many encryption algorithms lose security if the same IV is used twice.

If different keys are derived for each sender, starting at the same Base IV is likely to satisfy this condition. If the same key is used for multiple senders, then the application needs to provide for a method of dividing the IV space up between the senders. This could be done by providing a different base point to start from or a different Partial IV to start with and restricting the number of messages to be sent before rekeying.

signature = Sign(message content, key)

valid = Verification(message content, key, signature)

signature, message sent = Sign(message content, key)

valid, message content = Verification(message sent, key, signature)

message content bytes:

The byte string provided by the application to be signed.

to-be-signed bytes:

The byte string passed into the signature algorithm.

recovered bytes:

The bytes recovered during the signature verification process.

• The to-be-signed bytes are not the same as the message content bytes. This is because we build a larger to-be-signed message during the signature processing. The length of the recovered bytes may exceed the length of the message content, but not the length of the to-be-signed bytes. This may lead to privacy considerations if, for example, the externally supplied data contains confidential information.
• There may be difficulties in determining where the recovered bytes match up with the to-be-signed bytes, because the recovered bytes contain data not in the message content bytes. One possible option would be to create a padding scheme to prevent that.
• Not all message recovery signature algorithms take the recovered bytes from the end of the to-be-signed bytes. This is a problem, because the message content bytes are at the end of the to-be-signed bytes. If the bytes to be recovered are taken from the start of the to-be-signed bytes, then, by default, none of the message content bytes may be included in the recovered bytes. One possible option to deal with this is to reverse the to-be-signed data in the event that recovered bytes are taken from the start rather than the end of the to-be-signed bytes.

• Secrets that are uniformly random. This is the type of secret that is created by a good random number generator.
• Secrets that are not uniformly random. This is the type of secret that is created by operations like key agreement.
• Secrets that are not random. This is the type of secret that people generate for things like passwords.

• The "protected" field MUST be a zero-length byte string unless it is used in the computation of the content key.
• The "alg" header parameter MUST be present.
• A header parameter identifying the shared secret SHOULD be present.
• The "ciphertext" field MUST be a zero-length byte string.
• The "recipients" field MUST be absent.

• The "protected" field MUST be a zero-length byte string if the key wrap algorithm is an AE algorithm.
• The "recipients" field is normally absent but can be used. Applications MUST deal with a recipient field being present that has an unsupported algorithm. Failing to decrypt that specific recipient is an acceptable way of dealing with it. Failing to process the message is not an acceptable way of dealing with it.
• The plaintext to be encrypted is the key from the next layer down (usually the content layer).
• At a minimum, the "unprotected" field MUST contain the "alg" header parameter and SHOULD contain a header parameter identifying the shared secret.

• The "protected" field MUST be a zero-length byte string.
• The plaintext to be encrypted is the key from the next layer down (usually the content layer).
• At a minimum, the "unprotected" field MUST contain the "alg" header parameter and SHOULD contain a parameter identifying the asymmetric key.

Ephemeral-Static (ES) DH:

The sender of the message creates a one-time DH key and uses a static key for the recipient. The use of the ephemeral sender key means that no additional random input is needed, as this is randomly generated for each message.

Static-Static (SS) DH:

A static key is used for both the sender and the recipient. The use of static keys allows for the recipient to get a weak version of data origination for the message. When Static-Static key agreement is used, then some piece of unique data for the KDF is required to ensure that a different key is created for each message.

• At a minimum, headers MUST contain the "alg" header parameter and SHOULD contain a header parameter identifying the recipient's asymmetric key.
• The headers SHOULD identify the sender's key for the Static-Static versions and MUST contain the sender's ephemeral key for the ephemeral-static versions.

encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK)

• The "protected" field is fed into the KDF context structure.
• The plaintext to be encrypted is the key from the next layer down (usually the content layer).
• The "alg" header parameter MUST be present in the layer.
• A header parameter identifying the recipient's key SHOULD be present. A header parameter identifying the sender's key SHOULD be present.

• The restriction applies to the encoding of the Sig_structure, the Enc_structure, and the MAC_structure.
• Encoding MUST be done using definite lengths, and the length of the (encoded) argument MUST be the minimum possible length. This means that the integer 1 is encoded as "0x01" and not "0x1801".
• Applications MUST NOT generate messages with the same label used twice as a key in a single map. Applications MUST NOT parse and process messages with the same label used twice as a key in a single map. Applications can enforce the parse-and-process requirement by using parsers that will fail the parse step or by using parsers that will pass all keys to the application, and the application can perform the check for duplicate keys.

• Applications need to determine the set of messages defined in this document that they will be using. The set of messages corresponds fairly directly to the needed set of security services and security levels.
• Applications may define new header parameters for a specific purpose. Applications will oftentimes select specific header parameters to use or not to use. For example, an application would normally state a preference for using either the IV or the Partial IV header parameter. If the Partial IV header parameter is specified, then the application also needs to define how the fixed portion of the IV is determined.
• When applications use externally defined authenticated data, they need to define how that data is encoded. This document assumes that the data will be provided as a byte string. More information can be found in Section 4.3.
• Applications need to determine the set of security algorithms that is to be used. When selecting the algorithms to be used as the mandatory-to-implement set, consideration should be given to choosing different types of algorithms when two are chosen for a specific purpose. An example of this would be choosing HMAC-SHA512 and AES-CMAC (Cipher-Based Message Authentication Code) as different MAC algorithms; the construction is vastly different between these two algorithms. This means that a weakening of one algorithm would be unlikely to lead to a weakening of the other algorithms. Of course, these algorithms do not provide the same level of security and thus may not be comparable for the desired security functionality. Additional guidance can be found in [BCP201].
• Applications may need to provide some type of negotiation or discovery method if multiple algorithms or message structures are permitted. The method can range from something as simple as requiring preconfiguration of the set of algorithms to providing a discovery method built into the protocol. S/MIME provided a number of different ways to approach the problem that applications could follow:
  • Advertising in the message (S/MIME capabilities) [RFC 8551].
  • Advertising in the certificate (capabilities extension) [RFC 4262].
  • Minimum requirements for the S/MIME, which have been updated over time [RFC 2633] [RFC 3851] [RFC 5751] [RFC 8551]. (Note that [RFC 2633] was obsoleted by [RFC 3851], which was obsoleted by [RFC 5751], which was obsoleted by [RFC 8551].)

Type name:

application

Subtype name:

cose

Required parameters:

N/A

Optional parameters:

cose-type

Encoding considerations:

binary

Security considerations:

See the Security Considerations section of RFC 9052.

Interoperability considerations:

N/A

Published specification:

RFC 9052

Applications that use this media type:

IoT applications sending security content over HTTP(S) transports.

Fragment identifier considerations:

N/A

Additional information:

• Deprecated alias names for this type: N/A
• Magic number(s): N/A
• File extension(s): cbor
• Macintosh file type code(s): N/A

Person & email address to contact for further information:

iesg@ietf.org

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

Jim Schaad

Change Controller:

IESG

Provisional registration?

No

Type name:

application

Subtype name:

cose-key

Required parameters:

N/A

Optional parameters:

N/A

Encoding considerations:

binary

Security considerations:

See the Security Considerations section of RFC 9052.

Interoperability considerations:

N/A

Published specification:

RFC 9052

Applications that use this media type:

Distribution of COSE-based keys for IoT applications.

Fragment identifier considerations:

N/A

Additional information:

• Deprecated alias names for this type: N/A
• Magic number(s): N/A
• File extension(s): cbor
• Macintosh file type code(s): N/A

Person & email address to contact for further information:

iesg@ietf.org

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

Jim Schaad

Change Controller:

IESG

Provisional registration?

No

Type name:

application

Subtype name:

cose-key-set

Required parameters:

N/A

Optional parameters:

N/A

Encoding considerations:

binary

Security considerations:

See the Security Considerations section of RFC 9052.

Interoperability considerations:

N/A

Published specification:

RFC 9052

Applications that use this media type:

Distribution of COSE-based keys for IoT applications.

Fragment identifier considerations:

N/A

Additional information:

• Deprecated alias names for this type: N/A
• Magic number(s): N/A
• File extension(s): cbor
• Macintosh file type code(s): N/A

Person & email address to contact for further information:

iesg@ietf.org

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

Jim Schaad

Change Controller:

IESG

Provisional registration?

No

• Point squatting should be discouraged. Reviewers are encouraged to get sufficient information for registration requests to ensure that the usage is not going to duplicate an existing registration and that the code point is likely to be used in deployments. The ranges tagged as private use are intended for testing purposes and closed environments; code points in other ranges should not be assigned for testing.
• Standards Track or BCP RFCs are required to register a code point in the Standards Action range. Specifications should exist for Specification Required ranges, but early assignment before an RFC is available is considered to be permissible. Specifications are needed for the first-come, first-served range if the points are expected to be used outside of closed environments in an interoperable way. When specifications are not provided, the description provided needs to have sufficient information to identify what the point is being used for.
• Experts should take into account the expected usage of fields when approving code point assignment. The fact that the Standards Action range is only available to Standards Track documents does not mean that a Standards Track document cannot have points assigned outside of that range. The length of the encoded value should be weighed against how many code points of that length are left and the size of device it will be used on.
• When algorithms are registered, vanity registrations should be discouraged. One way to do this is to require registrations to provide additional documentation on security analysis of the algorithm. Another thing that should be considered is requesting an opinion on the algorithm from the Crypto Forum Research Group (CFRG). Algorithms are expected to meet the security requirements of the community and the requirements of the message structures in order to be suitable for registration.

• Use of the same key for two different algorithms can leak information about the key. It is therefore recommended that keys be restricted to a single algorithm.
• Use of "direct" as a recipient algorithm combined with a second recipient algorithm exposes the direct key to the second recipient; Section 8.5 forbids combining "direct" recipient algorithms with other modes.
• Several of the algorithms in [RFC 9053] have limits on the number of times that a key can be used without leaking information about the key.

• What are the permissions associated with the key owner?
• Is the cryptographic algorithm acceptable in the current context?
• Have the restrictions associated with the key, such as algorithm or freshness, been checked, and are they correct?
• Is the request something that is reasonable, given the current state of the application?
• Have any security considerations that are part of the message been enforced (as specified by the application or "crit" header parameter)?

[RFC2119]

S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC8174]

B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.

[RFC9053]

J Schaad, "CBOR Object Signing and Encryption (COSE): Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, August 2022,
<https://www.rfc-editor.org/info/rfc9053>.

[STD94]

C. Bormann, and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, December 2020,
<https://www.rfc-editor.org/info/std94>.

[BCP201]

R. Housley, "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, November 2015,
<https://www.rfc-editor.org/info/bcp201>.

[COAP.Formats]

IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/>.

[CORE-GROUPCOMM]

RISE AB, , , and , "Group Communication for the Constrained Application Protocol (CoAP)", Internet-Draft draft-ietf-core-groupcomm-bis-07, July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-groupcomm-bis-07>.

[COSE-COUNTERSIGN]

Vigil Security, LLC, , and , "CBOR Object Signing and Encryption (COSE): Countersignatures", Internet-Draft draft-ietf-cose-countersign-08, August 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-countersign-08>.

[COSE.Algorithms]

IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/>.

[COSE.KeyParameters]

IANA, "COSE Key Common Parameters",
<https://www.iana.org/assignments/cose/>.

[COSE.KeyTypes]

IANA, "COSE Key Types",
<https://www.iana.org/assignments/cose/>.

[DSS]

National Institute of Standards and Technology, "Digital Signature Standard (DSS)", FIPS 186-4, DOI 10.6028/NIST.FIPS.186-4, July 2013,
<https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf>.

[GitHub-Examples]

"GitHub Examples of COSE", June 2020,
<https://github.com/cose-wg/Examples>.

[PVSig]

D.R.L. Brown, and D.B. Johnson, "Formal Security Proofs for a Signature Scheme with Partial Message Recovery", DOI 10.1007/3-540-45353-9_11, June 2000,
<https://www.certicom.com/content/dam/certicom/images/pdfs/CerticomWP-PVSigSec_login.pdf>.

[RFC2633]

B. Ramsdell, "S/MIME Version 3 Message Specification", RFC 2633, DOI 10.17487/RFC2633, June 1999,
<https://www.rfc-editor.org/info/rfc2633>.

[RFC3394]

J. Schaad, and R. Housley, "Advanced Encryption Standard (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394, September 2002,
<https://www.rfc-editor.org/info/rfc3394>.

[RFC3851]

B. Ramsdell, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification", RFC 3851, DOI 10.17487/RFC3851, July 2004,
<https://www.rfc-editor.org/info/rfc3851>.

[RFC4262]

S. Santesson, "X.509 Certificate Extension for Secure/Multipurpose Internet Mail Extensions (S/MIME) Capabilities", RFC 4262, DOI 10.17487/RFC4262, December 2005,
<https://www.rfc-editor.org/info/rfc4262>.

[RFC4949]

R. Shirey, "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.

[RFC5116]

D. McGrew, "An Interface and Algorithms for Authenticated Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.

[RFC5652]

R. Housley, "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.

[RFC5751]

B. Ramsdell, and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, DOI 10.17487/RFC5751, January 2010,
<https://www.rfc-editor.org/info/rfc5751>.

[RFC5752]

S. Turner, and J. Schaad, "Multiple Signatures in Cryptographic Message Syntax (CMS)", RFC 5752, DOI 10.17487/RFC5752, January 2010,
<https://www.rfc-editor.org/info/rfc5752>.

[RFC5990]

J. Randall, B. Kaliski, J. Brainard, and S. Turner, "Use of the RSA-KEM Key Transport Algorithm in the Cryptographic Message Syntax (CMS)", RFC 5990, DOI 10.17487/RFC5990, September 2010,
<https://www.rfc-editor.org/info/rfc5990>.

[RFC6838]

N. Freed, J. Klensin, and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.

[RFC7252]

Z. Shelby, K. Hartke, and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.

[RFC7515]

M. Jones, J. Bradley, and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015,
<https://www.rfc-editor.org/info/rfc7515>.

[RFC7516]

M. Jones, and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.

[RFC7517]

M. Jones, "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.

[RFC7518]

M. Jones, "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.

[RFC8032]

S. Josefsson, and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.

[RFC8126]

M. Cotton, B. Leiba, and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8152]

J. Schaad, "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.

[RFC8230]

M. Jones, "Using RSA Algorithms with CBOR Object Signing and Encryption (COSE) Messages", RFC 8230, DOI 10.17487/RFC8230, September 2017,
<https://www.rfc-editor.org/info/rfc8230>.

[RFC8551]

J. Schaad, B. Ramsdell, and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", RFC 8551, DOI 10.17487/RFC8551, April 2019,
<https://www.rfc-editor.org/info/rfc8551>.

[RFC8610]

H. Birkholz, C. Vigano, and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019,
<https://www.rfc-editor.org/info/rfc8610>.

[RFC8613]

G. Selander, J. Mattsson, F. Palombini, and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.

[RFC9054]

J Schaad, "CBOR Object Signing and Encryption (COSE): Hash Algorithms", RFC 9054, DOI 10.17487/RFC9054, August 2022,
<https://www.rfc-editor.org/info/rfc9054>.

[RFC9106]

A. Biryukov, D. Dinu, D. Khovratovich, and S. Josefsson, "Argon2 Memory-Hard Function for Password Hashing and Proof-of-Work Applications", RFC 9106, DOI 10.17487/RFC9106, September 2021,
<https://www.rfc-editor.org/info/rfc9106>.

[STD90]

T. Bray, "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, December 2017,
<https://www.rfc-editor.org/info/std90>.

[W3C.WebCrypto]

M. Watson, "Web Cryptography API", January 2017,
<https://www.w3.org/TR/WebCryptoAPI/>.

• Applications need to list the set of COSE structures that implicit algorithms are to be used in. Applications need to require that the receipt of an explicit algorithm identifier in one of these structures will lead to the message being rejected. This requirement is stated so that there will never be a case where there is any ambiguity about the question of which algorithm should be used, the implicit or the explicit one. This applies even if the transported algorithm identifier is a protected attribute. This applies even if the transported algorithm is the same as the implicit algorithm.
• Applications need to define the set of information that is to be considered to be part of a context when omitting algorithm identifiers. At a minimum, this would be the key identifier (if needed), the key, the algorithm, and the COSE structure it is used with. Applications should restrict the use of a single key to a single algorithm. As noted for some of the algorithms in [RFC 9053], the use of the same key in different, related algorithms can lead to leakage of information about the key, leakage about the data, or the ability to perform forgeries.
• In many cases, applications that make the algorithm identifier implicit will also want to make the context identifier implicit for the same reason. That is, omitting the context identifier will decrease the message size (potentially significantly, depending on the length of the identifier). Applications that do this will need to describe the circumstances where the context identifier is to be omitted and how the context identifier is to be inferred in these cases. (An exhaustive search over all of the keys would normally not be considered to be acceptable.) An example of how this can be done is to tie the context to a transaction identifier. Both would be sent on the original message, but only the transaction identifier would need to be sent after that point, as the context is tied into the transaction identifier. Another way would be to associate a context with a network address. All messages coming from a single network address can be assumed to be associated with a specific context. (In this case, the address would normally be distributed as part of the context.)
• Applications cannot rely on key identifiers being unique unless they take significant efforts to ensure that they are computed in such a way as to create this guarantee. Even when an application does this, the uniqueness might be violated if the application is run in different contexts (i.e., with a different context provider) or if the system combines the security contexts from different applications together into a single store.
• Applications should continue the practice of protecting the algorithm identifier. Since this is not done by placing it in the protected attributes field, applications should define an application-specific external data structure that includes this value. This external data field can be used as such for content encryption, MAC, and signature algorithms. It can be used in the SuppPrivInfo field for those algorithms that use a KDF to derive a key value. Applications may also want to protect other information that is part of the context structure as well. It should be noted that those fields, such as the key or a Base IV, that are protected by virtue of being used in the cryptographic computation do not need to be included in the external data field.

• Applications that want to support this will need to define a structure that allows for, and clearly identifies, both the COSE structure to be used with a given key and the structure and algorithm to be used for the secondary layer. The key for the secondary layer is computed as normal from the recipient layer.

• Two contexts are distributed as a pair. Each of the contexts is for use with a COSE_Encrypt message. Each context will consist of distinct secret keys and IVs and potentially even different algorithms. One context is for sending messages from party A to party B, and the second context is for sending messages from party B to party A. This means that there is no chance for a reflection attack to occur, as each party uses different secret keys to send its messages; a message that is reflected back to it would fail to decrypt.
• Two contexts are distributed as a pair. The first context is used for encryption of the message, and the second context is used to place a countersignature on the message. The intention is that the second context can be distributed to other entities independently of the first context. This allows these entities to validate that the message came from an individual without being able to decrypt the message and see the content.
• Two contexts are distributed as a pair. The first context contains a key for dealing with MACed messages, and the second context contains a different key for dealing with encrypted messages. This allows for a unified distribution of keys to participants for different types of messages that have different keys, but where the keys may be used in a coordinated manner.

• Applications need to ensure that the multiple contexts stay associated. If one of the contexts is invalidated for any reason, all of the contexts associated with it should also be invalidated.

• Layer 0: The content encryption layer. This layer contains the payload of the message.
• Layer 1: The encryption of the CEK by a KEK.
• Layer 2: The encryption of a long random secret using an RSA key and a key derivation function to convert that secret into the KEK.

• Layer 0: Has content encrypted with AES-GCM using a 128-bit key.
• Layer 1: Uses the AES Key Wrap algorithm with a 128-bit key.
• Layer 2: Uses ECDH Ephemeral-Static direct to generate the Layer 1 key.

96(
  [ / COSE_Encrypt /
    / protected h'a10101' / << {
        / alg / 1:1 / AES-GCM 128 /
      } >>,
    / unprotected / {
      / iv / 5:h'02d1f7e6f26c43d4868d87ce'
    },
    / ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e2852948658f0
811139868826e89218a75715b',
    / recipients / [
      [ / COSE_Recipient /
        / protected / h'',
        / unprotected / {
          / alg / 1:-3 / A128KW /
        },
        / ciphertext / h'dbd43c4e9d719c27c6275c67d628d493f090593db82
18f11',
        / recipients / [
          [ / COSE_Recipient /
            / protected h'a1013818' / << {
                / alg / 1:-25 / ECDH-ES + HKDF-256 /
              } >> ,
            / unprotected / {
              / ephemeral / -1:{
                / kty / 1:2,
                / crv / -1:1,
                / x / -2:h'b2add44368ea6d641f9ca9af308b4079aeb519f11
e9b8a55a600b21233e86e68',
                / y / -3:false
              },
              / kid / 4:'meriadoc.brandybuck@buckland.example'
            },
            / ciphertext / h''
          ]
        ]
      ]
    ]
  ]
)

• Signature Algorithm: ECDSA w/ SHA-256, Curve P-256

98(
  [
    / protected / h'',
    / unprotected / {},
    / payload / 'This is the content.',
    / signatures / [
      [
        / protected h'a10126' / << {
            / alg / 1:-7 / ECDSA 256 /
          } >>,
        / unprotected / {
          / kid / 4:'11'
        },
        / signature / h'e2aeafd40d69d19dfe6e52077c5d7ff4e408282cbefb
5d06cbf414af2e19d982ac45ac98b8544c908b4507de1e90b717c3d34816fe926a2b
98f53afd2fa0f30a'
      ]
    ]
  ]
)

• Signature Algorithm: ECDSA w/ SHA-256, Curve P-256
• Signature Algorithm: ECDSA w/ SHA-512, Curve P-521

98(
  [
    / protected / h'',
    / unprotected / {},
    / payload / 'This is the content.',
    / signatures / [
      [
        / protected h'a10126' / << {
            / alg / 1:-7 / ECDSA 256 /
          } >>,
        / unprotected / {
          / kid / 4:'11'
        },
        / signature / h'e2aeafd40d69d19dfe6e52077c5d7ff4e408282cbefb
5d06cbf414af2e19d982ac45ac98b8544c908b4507de1e90b717c3d34816fe926a2b
98f53afd2fa0f30a'
      ],
      [
        / protected h'a1013823' / << {
            / alg / 1:-36 / ECDSA 521 /
          } >> ,
        / unprotected / {
          / kid / 4:'bilbo.baggins@hobbiton.example'
        },
        / signature / h'00a2d28a7c2bdb1587877420f65adf7d0b9a06635dd1
de64bb62974c863f0b160dd2163734034e6ac003b01e8705524c5c4ca479a952f024
7ee8cb0b4fb7397ba08d009e0c8bf482270cc5771aa143966e5a469a09f613488030
c5b07ec6d722e3835adb5b2d8c44e95ffb13877dd2582866883535de3bb03d01753f
83ab87bb4f7a0297'
      ]
    ]
  ]
)

• Signature Algorithm: ECDSA w/ SHA-256, Curve P-256
• There is a criticality marker on the "reserved" header parameter.

98(
  [
    / protected h'a2687265736572766564f40281687265736572766564' /
    << {
        "reserved":false,
        / crit / 2:[
          "reserved"
        ]
      } >>,
    / unprotected / {},
    / payload / 'This is the content.',
    / signatures / [
      [
        / protected h'a10126' / << {
            / alg / 1:-7 / ECDSA 256 /
          } >>,
        / unprotected / {
          / kid / 4:'11'
        },
        / signature / h'3fc54702aa56e1b2cb20284294c9106a63f91bac658d
69351210a031d8fc7c5ff3e4be39445b1a3e83e1510d1aca2f2e8a7c081c7645042b
18aba9d1fad1bd9c'
      ]
    ]
  ]
)

• Signature Algorithm: ECDSA w/ SHA-256, Curve P-256

18(
  [
    / protected h'a10126' / << {
        / alg / 1:-7 / ECDSA 256 /
      } >>,
    / unprotected / {
      / kid / 4:'11'
    },
    / payload / 'This is the content.',
    / signature / h'8eb33e4ca31d1c465ab05aac34cc6b23d58fef5c083106c4
d25a91aef0b0117e2af9a291aa32e14ab834dc56ed2a223444547e01f11d3b0916e5
a4c345cacb36'
  ]
)

• CEK: AES-GCM w/ 128-bit key
• Recipient class: ECDH Ephemeral-Static, Curve P-256

96(
  [
    / protected h'a10101' / << {
        / alg / 1:1 / AES-GCM 128 /
      } >>,
    / unprotected / {
      / iv / 5:h'c9cf4df2fe6c632bf7886413'
    },
    / ciphertext / h'7adbe2709ca818fb415f1e5df66f4e1a51053ba6d65a1a0
c52a357da7a644b8070a151b0',
    / recipients / [
      [
        / protected h'a1013818' / << {
            / alg / 1:-25 / ECDH-ES + HKDF-256 /
          } >>,
        / unprotected / {
          / ephemeral / -1:{
            / kty / 1:2,
            / crv / -1:1,
            / x / -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbf
bf054e1c7b4d91d6280',
            / y / -3:true
          },
          / kid / 4:'meriadoc.brandybuck@buckland.example'
        },
        / ciphertext / h''
      ]
    ]
  ]
)

• CEK: AES-CCM w/ 128-bit key, truncate the tag to 64 bits
• Recipient class: Use HKDF on a shared secret with the following implicit fields as part of the context.
  • salt: "aabbccddeeffgghh"
  • PartyU identity: "lighting-client"
  • PartyV identity: "lighting-server"
  • Supplementary Public Other: "Encryption Example 02"

96(
  [
    / protected h'a1010a' / << {
        / alg / 1:10 / AES-CCM-16-64-128 /
      } >>,
    / unprotected / {
      / iv / 5:h'89f52f65a1c580933b5261a76c'
    },
    / ciphertext / h'753548a19b1307084ca7b2056924ed95f2e3b17006dfe93
1b687b847',
    / recipients / [
      [
        / protected h'a10129' / << {
            / alg / 1:-10
          } >>,
        / unprotected / {
          / salt / -20:'aabbccddeeffgghh',
          / kid / 4:'our-secret'
        },
        / ciphertext / h''
      ]
    ]
  ]
)

• CEK: AES-GCM w/ 128-bit key
• Recipient class: ECDH Static-Static, Curve P-256 with AES Key Wrap
• Externally Supplied AAD: h'0011bbcc22dd44ee55ff660077'

96(
  [
    / protected h'a10101' / << {
        / alg / 1:1 / AES-GCM 128 /
      } >> ,
    / unprotected / {
      / iv / 5:h'02d1f7e6f26c43d4868d87ce'
    },
    / ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e28529d8f5335
e5f0165eee976b4a5f6c6f09d',
    / recipients / [
      [
        / protected / h'a101381f' / {
            \ alg \ 1:-32 \ ECDH-SS+A128KW \
          } / ,
        / unprotected / {
          / static kid / -3:'peregrin.took@tuckborough.example',
          / kid / 4:'meriadoc.brandybuck@buckland.example',
          / U nonce / -22:h'0101'
        },
        / ciphertext / h'41e0d76f579dbd0d936a662d54d8582037de2e366fd
e1c62'
      ]
    ]
  ]
)

• CEK: AES-CCM w/ 128-bit key and a 64-bit tag

16(
  [
    / protected h'a1010a' / << {
        / alg / 1:10 / AES-CCM-16-64-128 /
      } >> ,
    / unprotected / {
      / iv / 5:h'89f52f65a1c580933b5261a78c'
    },
    / ciphertext / h'5974e1b99a3a4cc09a659aa2e9e7fff161d38ce71cb45ce
460ffb569'
  ]
)

• CEK: AES-CCM w/ 128-bit key and a 64-bit tag
• Prefix for IV is 89F52F65A1C580933B52

16(
  [
    / protected h'a1010a' / << {
        / alg / 1:10 / AES-CCM-16-64-128 /
      } >> ,
    / unprotected / {
      / partial iv / 6:h'61a7'
    },
    / ciphertext / h'252a8911d465c125b6764739700f0141ed09192de139e05
3bd09abca'
  ]
)

• MAC: AES-CMAC, 256-bit key, truncated to 64 bits
• Recipient class: direct shared secret

97(
  [
    / protected h'a1010f' / << {
        / alg / 1:15 / AES-CBC-MAC-256//64 /
      } >> ,
    / unprotected / {},
    / payload / 'This is the content.',
    / tag / h'9e1226ba1f81b848',
    / recipients / [
      [
        / protected / h'',
        / unprotected / {
          / alg / 1:-6 / direct /,
          / kid / 4:'our-secret'
        },
        / ciphertext / h''
      ]
    ]
  ]
)

• MAC: HMAC w/SHA-256, 256-bit key
• Recipient class: ECDH key agreement, two static keys, HKDF w/context structure

97(
  [
    / protected h'a10105' / << {
        / alg / 1:5 / HMAC 256//256 /
      } >> ,
    / unprotected / {},
    / payload / 'This is the content.',
    / tag / h'81a03448acd3d305376eaa11fb3fe416a955be2cbe7ec96f012c99
4bc3f16a41',
    / recipients / [
      [
        / protected h'a101381a' / << {
            / alg / 1:-27 / ECDH-SS + HKDF-256 /
          } >> ,
        / unprotected / {
          / static kid / -3:'peregrin.took@tuckborough.example',
          / kid / 4:'meriadoc.brandybuck@buckland.example',
          / U nonce / -22:h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d
19558ccfec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a583
68b017e7f2a9e5ce4db5'
        },
        / ciphertext / h''
      ]
    ]
  ]
)

• MAC: AES-MAC, 128-bit key, truncated to 64 bits
• Recipient class: AES Key Wrap w/ a preshared 256-bit key

97(
  [
    / protected h'a1010e' / << {
        / alg / 1:14 / AES-CBC-MAC-128//64 /
      } >> ,
    / unprotected / {},
    / payload / 'This is the content.',
    / tag / h'36f5afaf0bab5d43',
    / recipients / [
      [
        / protected / h'',
        / unprotected / {
          / alg / 1:-5 / A256KW /,
          / kid / 4:'018c0ae5-4d9b-471b-bfd6-eef314bc7037'
        },
        / ciphertext / h'711ab0dc2fc4585dce27effa6781c8093eba906f227
b6eb0'
      ]
    ]
  ]
)

• MAC: HMAC w/ SHA-256, 128-bit key
• Recipient class: Uses two different methods.
  1. ECDH Ephemeral-Static, Curve P-521, AES Key Wrap w/ 128-bit key
  2. AES Key Wrap w/ 256-bit key

97(
  [
    / protected h'a10105' / << {
        / alg / 1:5 / HMAC 256//256 /
      } >> ,
    / unprotected / {},
    / payload / 'This is the content.',
    / tag / h'bf48235e809b5c42e995f2b7d5fa13620e7ed834e337f6aa43df16
1e49e9323e',
    / recipients / [
      [
        / protected h'a101381c' / << {
            / alg / 1:-29 / ECDH-ES+A128KW /
          } >> ,
        / unprotected / {
          / ephemeral / -1:{
            / kty / 1:2,
            / crv / -1:3,
            / x / -2:h'0043b12669acac3fd27898ffba0bcd2e6c366d53bc4db
71f909a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2
d613574e7dc242f79c3',
            / y / -3:true
          },
          / kid / 4:'bilbo.baggins@hobbiton.example'
        },
        / ciphertext / h'339bc4f79984cdc6b3e6ce5f315a4c7d2b0ac466fce
a69e8c07dfbca5bb1f661bc5f8e0df9e3eff5'
      ],
      [
        / protected / h'',
        / unprotected / {
          / alg / 1:-5 / A256KW /,
          / kid / 4:'018c0ae5-4d9b-471b-bfd6-eef314bc7037'
        },
        / ciphertext / h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a
518e7736549e998370695e6d6a83b4ae507bb'
      ]
    ]
  ]
)

• MAC: AES-CMAC, 256-bit key, truncated to 64 bits
• Recipient class: direct shared secret

17(
  [
    / protected h'a1010f' / << {
        / alg / 1:15 / AES-CBC-MAC-256//64 /
      } >> ,
    / unprotected / {},
    / payload / 'This is the content.',
    / tag / h'726043745027214f'
  ]
)

• An EC key with a kid of "meriadoc.brandybuck@buckland.example"
• An EC key with a kid of "11"
• An EC key with a kid of "bilbo.baggins@hobbiton.example"
• An EC key with a kid of "peregrin.took@tuckborough.example"

[
  {
    -1:1,
    -2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0
8551d',
    -3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008
4d19c',
    1:2,
    2:'meriadoc.brandybuck@buckland.example'
  },
  {
    -1:1,
    -2:h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a
09eff',
    -3:h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbf
c117e',
    1:2,
    2:'11'
  },
  {
    -1:3,
    -2:h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737bf5de
7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620085e5c8
f42ad',
    -3:h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e247e
60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f3fe1ea1
d9475',
    1:2,
    2:'bilbo.baggins@hobbiton.example'
  },
  {
    -1:1,
    -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b4d91
d6280',
    -3:h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e03bf
822bb',
    1:2,
    2:'peregrin.took@tuckborough.example'
  }
]

• An EC key with a kid of "meriadoc.brandybuck@buckland.example"
• An EC key with a kid of "11"
• An EC key with a kid of "bilbo.baggins@hobbiton.example"
• A shared-secret key with a kid of "our-secret"
• An EC key with a kid of "peregrin.took@tuckborough.example"
• A shared-secret key with kid "our-secret2"
• A shared-secret key with a kid of "018c0ae5-4d9b-471b-bfd6-eef314bc7037"

[
  {
    1:2,
    2:'meriadoc.brandybuck@buckland.example',
    -1:1,
    -2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0
8551d',
    -3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008
4d19c',
    -4:h'aff907c99f9ad3aae6c4cdf21122bce2bd68b5283e6907154ad911840fa
208cf'
  },
  {
    1:2,
    2:'11',
    -1:1,
    -2:h'bac5b11cad8f99f9c72b05cf4b9e26d244dc189f745228255a219a86d6a
09eff',
    -3:h'20138bf82dc1b6d562be0fa54ab7804a3a64b6d72ccfed6b6fb6ed28bbf
c117e',
    -4:h'57c92077664146e876760c9520d054aa93c3afb04e306705db609030850
7b4d3'
  },
  {
    1:2,
    2:'bilbo.baggins@hobbiton.example',
    -1:3,
    -2:h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737bf5de
7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620085e5c8
f42ad',
    -3:h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e247e
60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f3fe1ea1
d9475',
    -4:h'00085138ddabf5ca975f5860f91a08e91d6d5f9a76ad4018766a476680b
55cd339e8ab6c72b5facdb2a2a50ac25bd086647dd3e2e6e99e84ca2c3609fdf177f
eb26d'
  },
  {
    1:4,
    2:'our-secret',
    -1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4
27188'
  },
  {
    1:2,
    -1:1,
    2:'peregrin.took@tuckborough.example',
    -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b4d91
d6280',
    -3:h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e03bf
822bb',
    -4:h'02d1f7e6f26c43d4868d87ceb2353161740aacf1f7163647984b522a848
df1c3'
  },
  {
    1:4,
    2:'our-secret2',
    -1:h'849b5786457c1491be3a76dcea6c4271'
  },
  {
    1:4,
    2:'018c0ae5-4d9b-471b-bfd6-eef314bc7037',
    -1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4
27188'
  }
]

Jim Schaad