RFC 8548
Cryptographic Protection of TCP Streams (tcpcrypt)
Pages: 32
Experimental
Experimental
Part 2 of 2 – Pages 18 to 32
4. Encodings
This section provides byte-level encodings for values transmitted or computed by the protocol.4.1. Key-Exchange Messages
The Init1 message has the following encoding: byte 0 1 2 3 +-------+-------+-------+-------+ | INIT1_MAGIC | | | +-------+-------+-------+-------+ 4 5 6 7 +-------+-------+-------+-------+ | message_len | | = M | +-------+-------+-------+-------+ 8 +--------+-----+----+-----+----+---...---+-----+-----+ |nciphers|sym_ |sym_ | |sym_ | | = K |cipher[0] |cipher[1] | |cipher[K-1]| +--------+-----+----+-----+----+---...---+-----+-----+ 2*K + 9 2*K + 9 + N_A_LEN | | v v +-------+---...---+-------+-------+---...---+-------+ | N_A | Pub_A | | | | +-------+---...---+-------+-------+---...---+-------+ M - 1 +-------+---...---+-------+ | ignored | | | +-------+---...---+-------+ The constant INIT1_MAGIC is defined in Section 4.3. The four-byte field message_len gives the length of the entire Init1 message, encoded as a big-endian integer. The nciphers field contains an integer value that specifies the number of two-byte symmetric-cipher identifiers that follow. The sym_cipher[i] identifiers indicate
cryptographic algorithms in Table 5 in Section 7. The length N_A_LEN and the length of Pub_A are both determined by the negotiated TEP as described in Section 5. Implementations of this protocol MUST construct Init1 such that the ignored field has zero length; that is, they MUST construct the message such that its end, as determined by message_len, coincides with the end of the field Pub_A. When receiving Init1, however, implementations MUST permit and ignore any bytes following Pub_A. The Init2 message has the following encoding: byte 0 1 2 3 +-------+-------+-------+-------+ | INIT2_MAGIC | | | +-------+-------+-------+-------+ 4 5 6 7 8 9 +-------+-------+-------+-------+-------+-------+ | message_len | sym_cipher | | = M | | +-------+-------+-------+-------+-------+-------+ 10 10 + N_B_LEN | | v v +-------+---...---+-------+-------+---...---+-------+ | N_B | Pub_B | | | | +-------+---...---+-------+-------+---...---+-------+ M - 1 +-------+---...---+-------+ | ignored | | | +-------+---...---+-------+ The constant INIT2_MAGIC is defined in Section 4.3. The four-byte field message_len gives the length of the entire Init2 message, encoded as a big-endian integer. The sym_cipher value is a selection from the symmetric-cipher identifiers in the previously-received Init1 message. The length N_B_LEN and the length of Pub_B are both determined by the negotiated TEP as described in Section 5.
Implementations of this protocol MUST construct Init2 such that the field "ignored" has zero length; that is, they MUST construct the message such that its end, as determined by message_len, coincides with the end of the Pub_B field. When receiving Init2, however, implementations MUST permit and ignore any bytes following Pub_B.4.2. Encryption Frames
An encryption frame comprises a control byte and a length-prefixed ciphertext value: byte 0 1 2 3 clen+2 +-------+-------+-------+-------+---...---+-------+ |control| clen | ciphertext | +-------+-------+-------+-------+---...---+-------+ The field clen is an integer in big-endian format and gives the length of the ciphertext field. The control field has this structure: bit 7 1 0 +-------+---...---+-------+-------+ | cres | rekey | +-------+---...---+-------+-------+ The seven-bit field cres is reserved; implementations MUST set these bits to zero when sending and MUST ignore them when receiving. The use of the rekey field is described in Section 3.8.4.2.1. Plaintext
The ciphertext field is the result of applying the negotiated authenticated-encryption algorithm to a plaintext value, which has one of these two formats: byte 0 1 plen-1 +-------+-------+---...---+-------+ | flags | data | +-------+-------+---...---+-------+ byte 0 1 2 3 plen-1 +-------+-------+-------+-------+---...---+-------+ | flags | urgent | data | +-------+-------+-------+-------+---...---+-------+
(Note that clen in the previous section will generally be greater
than plen, as the ciphertext produced by the authenticated-encryption
scheme both encrypts the application data and provides redundancy
with which to verify its integrity.)
The flags field has this structure:
bit 7 6 5 4 3 2 1 0
+----+----+----+----+----+----+----+----+
| fres |URGp|FINp|
+----+----+----+----+----+----+----+----+
The six-bit field fres is reserved; implementations MUST set these
six bits to zero when sending, and MUST ignore them when receiving.
When the URGp bit is set, it indicates that the urgent field is
present, and thus that the plaintext value has the second structure
variant above; otherwise, the first variant is used.
The meaning of the urgent field and of the flag bits is described in
Section 3.7.
4.2.2. Associated Data
An encryption frame's associated data (which is supplied to the AEAD
algorithm when decrypting the ciphertext and verifying the frame's
integrity) has this format:
byte 0 1 2
+-------+-------+-------+
|control| clen |
+-------+-------+-------+
It contains the same values as the frame's control and clen fields.
4.2.3. Frame ID
Lastly, a frame ID (used to construct the nonce for the AEAD
algorithm) has this format:
byte 0 ae_nonce_len - 8 ae_nonce_len - 1
| | |
v v v
+-----+--...--+-----+-----+--...--+-----+
| 0 | | 0 | offset |
+-----+--...--+-----+-----+--...--+-----+
The 8-byte offset field contains an integer in big-endian format. Its value is specified in Section 3.6. Zero-valued bytes are prepended to the offset field to form a structure of length ae_nonce_len.4.3. Constant Values
The table below defines values for the constants used in the protocol. +------------+--------------+ | Value | Name | +------------+--------------+ | 0x01 | CONST_NEXTK | | 0x02 | CONST_SESSID | | 0x03 | CONST_REKEY | | 0x04 | CONST_KEY_A | | 0x05 | CONST_KEY_B | | 0x06 | CONST_RESUME | | 0x15101a0e | INIT1_MAGIC | | 0x097105e0 | INIT2_MAGIC | +------------+--------------+ Table 1: Constant Values Used in the Protocol5. Key-Agreement Schemes
The TEP negotiated via TCP-ENO indicates the use of one of the key- agreement schemes named in Table 4 in Section 7. For example, TCPCRYPT_ECDHE_P256 names the tcpcrypt protocol using ECDHE-P256 together with the CPRF and length parameters specified below. All the TEPs specified in this document require the use of HKDF- Expand-SHA256 as the CPRF, and these lengths for nonces and session secrets: N_A_LEN: 32 bytes N_B_LEN: 32 bytes K_LEN: 32 bytes Future documents assigning additional TEPs for use with tcpcrypt might specify different values for the lengths above. Note that the minimum session ID length specified by TCP-ENO, together with the way tcpcrypt constructs session IDs, implies that K_LEN MUST have length at least 32 bytes. Key-agreement schemes ECDHE-P256 and ECDHE-P521 employ the Elliptic Curve Secret Value Derivation Primitive, Diffie-Hellman version
(ECSVDP-DH) defined in [IEEE-1363]. The named curves are defined in [NIST-DSS]. When the public-key values Pub_A and Pub_B are transmitted as described in Section 4.1, they are encoded with the "Elliptic Curve Point to Octet String Conversion Primitive" described in Section E.2.3 of [IEEE-1363] and are prefixed by a two-byte length in big-endian format: byte 0 1 2 L - 1 +-------+-------+-------+---...---+-------+ | pubkey_len | pubkey | | = L | | +-------+-------+-------+---...---+-------+ Implementations MUST encode these pubkey values in "compressed format". Implementations MUST validate these pubkey values according to the algorithm in Section A.16.10 of [IEEE-1363]. Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 perform the Diffie-Hellman protocol using the functions X25519 and X448, respectively. Implementations SHOULD compute these functions using the algorithms described in [RFC7748]. When they do so, implementations MUST check whether the computed Diffie-Hellman shared secret is the all-zero value and abort if so, as described in Section 6 of [RFC7748]. Alternative implementations of these functions SHOULD abort when either input forces the shared secret to one of a small set of values as discussed in Section 7 of [RFC7748]. For these schemes, public-key values Pub_A and Pub_B are transmitted directly with no length prefix: 32 bytes for ECDHE-Curve25519 and 56 bytes for ECDHE-Curve448. Table 2 below specifies the requirement levels of the four TEPs specified in this document. In particular, all implementations of tcpcrypt MUST support TCPCRYPT_ECDHE_Curve25519. However, system administrators MAY configure which TEPs a host will negotiate independent of these implementation requirements. +-------------+---------------------------+ | Requirement | TEP | +-------------+---------------------------+ | REQUIRED | TCPCRYPT_ECDHE_Curve25519 | | RECOMMENDED | TCPCRYPT_ECDHE_Curve448 | | OPTIONAL | TCPCRYPT_ECDHE_P256 | | OPTIONAL | TCPCRYPT_ECDHE_P521 | +-------------+---------------------------+ Table 2: Requirements for Implementation of TEPs
6. AEAD Algorithms
This document uses sym_cipher identifiers in the messages Init1 and Init2 (see Section 3.3) to negotiate the use of AEAD algorithms; the values of these identifiers are given in Table 5 in Section 7. The algorithms AEAD_AES_128_GCM and AEAD_AES_256_GCM are specified in [RFC5116]. The algorithm AEAD_CHACHA20_POLY1305 is specified in [RFC8439]. Implementations MUST support certain AEAD algorithms according to Table 3. Note that system administrators MAY configure which algorithms a host will negotiate independently of these requirements. Lastly, this document uses the lengths ae_key_len and ae_nonce_len to specify aspects of encryption and data formats. These values depend on the negotiated AEAD algorithm, also according to the table below. +------------------------+-------------+------------+--------------+ | AEAD Algorithm | Requirement | ae_key_len | ae_nonce_len | +------------------------+-------------+------------+--------------+ | AEAD_AES_128_GCM | REQUIRED | 16 bytes | 12 bytes | | AEAD_AES_256_GCM | RECOMMENDED | 32 bytes | 12 bytes | | AEAD_CHACHA20_POLY1305 | RECOMMENDED | 32 bytes | 12 bytes | +------------------------+-------------+------------+--------------+ Table 3: Requirement and Lengths for Each AEAD Algorithm7. IANA Considerations
For use with TCP-ENO's negotiation mechanism, tcpcrypt's TEP identifiers have been incorporated in IANA's "TCP Encryption Protocol Identifiers" registry under the "Transmission Control Protocol (TCP) Parameters" registry, as in Table 4. The various key-agreement schemes used by these tcpcrypt variants are defined in Section 5. +-------+---------------------------+-----------+ | Value | Meaning | Reference | +-------+---------------------------+-----------+ | 0x21 | TCPCRYPT_ECDHE_P256 | [RFC8548] | | 0x22 | TCPCRYPT_ECDHE_P521 | [RFC8548] | | 0x23 | TCPCRYPT_ECDHE_Curve25519 | [RFC8548] | | 0x24 | TCPCRYPT_ECDHE_Curve448 | [RFC8548] | +-------+---------------------------+-----------+ Table 4: TEP Identifiers for Use with tcpcrypt In Section 6, this document defines the use of several AEAD algorithms for encrypting application data. To name these
algorithms, the tcpcrypt protocol uses two-byte identifiers in the range 0x0001 to 0xFFFF, inclusively, for which IANA maintains a new "tcpcrypt AEAD Algorithms" registry under the "Transmission Control Protocol (TCP) Parameters" registry. The initial values for this registry are given in Table 5. Future assignments are to be made upon satisfying either of two policies defined in [RFC8126]: "IETF Review" or (for non-IETF stream specifications) "Expert Review with RFC Required." IANA will furthermore provide early allocation [RFC7120] to facilitate testing before RFCs are finalized. +--------+------------------------+----------------------+ | Value | AEAD Algorithm | Reference | +--------+------------------------+----------------------+ | 0x0001 | AEAD_AES_128_GCM | [RFC8548], Section 6 | | 0x0002 | AEAD_AES_256_GCM | [RFC8548], Section 6 | | 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC8548], Section 6 | +--------+------------------------+----------------------+ Table 5: Authenticated-Encryption Algorithms for Use with tcpcrypt8. Security Considerations
All of the security considerations of TCP-ENO apply to tcpcrypt. In particular, tcpcrypt does not protect against active network attackers unless applications authenticate the session ID. If it can be established that the session IDs computed at each end of the connection match, then tcpcrypt guarantees that no man-in-the-middle attacks occurred unless the attacker has broken the underlying cryptographic primitives, e.g., Elliptic Curve Diffie-Hellman (ECDH). A proof of this property for an earlier version of the protocol has been published [tcpcrypt]. To ensure middlebox compatibility, tcpcrypt does not protect TCP headers. Therefore, the protocol is vulnerable to denial-of-service from off-path attackers just as plain TCP is. Possible attacks include desynchronizing the underlying TCP stream, injecting RST or FIN segments, and forging rekey bits. These attacks will cause a tcpcrypt connection to hang or fail with an error, but not in any circumstance where plain TCP could continue uncorrupted. Implementations MUST give higher-level software a way to distinguish such errors from a clean end-of-stream (indicated by an authenticated FINp bit) so that applications can avoid semantic truncation attacks. There is no "key confirmation" step in tcpcrypt. This is not needed because tcpcrypt's threat model includes the possibility of a connection to an adversary. If key negotiation is compromised and yields two different keys, failed integrity checks on every subsequent frame will cause the connection either to hang or to
abort. This is not a new threat as an active attacker can achieve the same results against a plain TCP connection by injecting RST segments or modifying sequence and acknowledgement numbers. Tcpcrypt uses short-lived public keys to provide forward secrecy; once an implementation removes these keys from memory, a compromise of the system will not provide any means to derive the session secrets for past connections. All currently-specified key agreement schemes involve key agreement based on Ephemeral Elliptic Curve Diffie-Hellman (ECDHE), meaning a new key pair can be efficiently computed for each connection. If implementations reuse these parameters, they MUST limit the lifetime of the private parameters as far as is practical in order to minimize the number of past connections that are vulnerable. Of course, placing private keys in persistent storage introduces severe risks that they will not be destroyed reliably and in a timely fashion, and it SHOULD be avoided whenever possible. Attackers cannot force passive openers to move forward in their session resumption chain without guessing the content of the resumption identifier, which will be difficult without key knowledge. The cipher-suites specified in this document all use HMAC-SHA256 to implement the collision-resistant pseudo-random function denoted by CPRF. A collision-resistant function is one for which, for sufficiently large L, an attacker cannot find two distinct inputs (K_1, CONST_1) and (K_2, CONST_2) such that CPRF(K_1, CONST_1, L) = CPRF(K_2, CONST_2, L). Collision resistance is important to assure the uniqueness of session IDs, which are generated using the CPRF. Lastly, many of tcpcrypt's cryptographic functions require random input, and thus any host implementing tcpcrypt MUST have access to a cryptographically-secure source of randomness or pseudo-randomness. [RFC4086] provides recommendations on how to achieve this. Most implementations will rely on a device's pseudo-random generator, seeded from hardware events and a seed carried over from the previous boot. Once a pseudo-random generator has been properly seeded, it can generate effectively arbitrary amounts of pseudo-random data. However, until a pseudo-random generator has been seeded with sufficient entropy, not only will tcpcrypt be insecure, it will reveal information that further weakens the security of the pseudo- random generator, potentially harming other applications. As REQUIRED by TCP-ENO, implementations MUST NOT send ENO options unless they have access to an adequate source of randomness.
8.1. Asymmetric Roles
Tcpcrypt transforms a shared pseudo-random key (PRK) into cryptographic traffic keys for each direction. Doing so requires an asymmetry in the protocol, as the key derivation function must be perturbed differently to generate different keys in each direction. Tcpcrypt includes other asymmetries in the roles of the two hosts, such as the process of negotiating algorithms (e.g., proposing vs. selecting cipher suites).8.2. Verified Liveness
Many hosts implement TCP keep-alives [RFC1122] as an option for applications to ensure that the other end of a TCP connection still exists even when there is no data to be sent. A TCP keep-alive segment carries a sequence number one prior to the beginning of the send window and may carry one byte of "garbage" data. Such a segment causes the remote side to send an acknowledgment. Unfortunately, tcpcrypt cannot cryptographically verify keep-alive acknowledgments. Therefore, an attacker could prolong the existence of a session at one host after the other end of the connection no longer exists. (Such an attack might prevent a process with sensitive data from exiting, giving an attacker more time to compromise a host and extract the sensitive data.) To counter this threat, tcpcrypt specifies a way to stimulate the remote host to send verifiably fresh and authentic data, described in Section 3.9. The TCP keep-alive mechanism has also been used for its effects on intermediate nodes in the network, such as preventing flow state from expiring at NAT boxes or firewalls. As these purposes do not require the authentication of endpoints, implementations MAY safely accomplish them using either the existing TCP keep-alive mechanism or tcpcrypt's verified keep-alive mechanism.8.3. Mandatory Key-Agreement Schemes
This document mandates that tcpcrypt implementations provide support for at least one key-agreement scheme: ECDHE using Curve25519. This choice of a single mandatory algorithm is the result of a difficult tradeoff between cryptographic diversity and the ease and security of actual deployment. The IETF's appraisal of best current practice on this matter [RFC7696] says, "Ideally, two independent sets of mandatory-to- implement algorithms will be specified, allowing for a primary suite
and a secondary suite. This approach ensures that the secondary suite is widely deployed if a flaw is found in the primary one." To meet that ideal, it might appear natural to also mandate ECDHE using P-256. However, implementing the Diffie-Hellman function using NIST elliptic curves (including those specified for use with tcpcrypt, P-256 and P-521) appears to be very difficult to achieve without introducing vulnerability to side-channel attacks [NIST-fail]. Although well-trusted implementations are available as part of large cryptographic libraries, these can be difficult to extract for use in operating-system kernels where tcpcrypt is usually best implemented. In contrast, the characteristics of Curve25519 together with its recent popularity has led to many safe and efficient implementations, including some that fit naturally into the kernel environment. [RFC7696] insists that, "The selected algorithms need to be resistant to side-channel attacks and also meet the performance, power, and code size requirements on a wide variety of platforms." On this principle, tcpcrypt excludes the NIST curves from the set of mandatory-to-implement key-agreement algorithms. Lastly, this document encourages support for key agreement with Curve448, categorizing it as RECOMMENDED. Curve448 appears likely to admit safe and efficient implementations. However, support is not REQUIRED because existing implementations might not yet be sufficiently well proven.9. Experiments
Some experience will be required to determine whether the tcpcrypt protocol can be deployed safely and successfully across the diverse environments of the global internet. Safety means that TCP implementations that support tcpcrypt are able to communicate reliably in all the same settings as they would without tcpcrypt. As described in Section 9 of [RFC8547], this property can be subverted if middleboxes strip ENO options from non-SYN segments after allowing them in SYN segments, or if the particular communication patterns of tcpcrypt offend the policies of middleboxes doing deep-packet inspection. Success, in addition to safety, means hosts that implement tcpcrypt actually enable encryption when connecting to one another. This property depends on the network's treatment of the TCP-ENO handshake and can be subverted if middleboxes merely strip unknown TCP options or terminate TCP connections and relay data back and forth unencrypted.
Ease of implementation will be a further challenge to deployment. Because tcpcrypt requires encryption operations on frames that may span TCP segments, kernel implementations are forced to buffer segments in different ways than are necessary for plain TCP. More implementation experience will show how much additional code complexity is required in various operating systems and what kind of performance effects can be expected.10. References
10.1. Normative References
[IEEE-1363] IEEE, "IEEE Standard Specifications for Public-Key Cryptography", IEEE Standard 1363-2000, DOI 10.1109/IEEESTD.2000.92292. [NIST-DSS] National Institute of Standards and Technology (NIST), "Digital Signature Standard (DSS)", FIPS PUB 186-4, DOI 10.6028/NIST.FIPS.186-4, July 2013. [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, <https://www.rfc-editor.org/info/rfc793>. [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP Selective Acknowledgment Options", RFC 2018, DOI 10.17487/RFC2018, October 1996, <https://www.rfc-editor.org/info/rfc2018>. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997, <https://www.rfc-editor.org/info/rfc2104>. [RFC2119] Bradner, S., "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>. [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, <https://www.rfc-editor.org/info/rfc5116>. [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, <https://www.rfc-editor.org/info/rfc5869>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January 2014, <https://www.rfc-editor.org/info/rfc7120>. [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, January 2016, <https://www.rfc-editor.org/info/rfc7748>. [RFC8126] Cotton, M., Leiba, B., 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>. [RFC8174] Leiba, B., "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>. [RFC8439] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018, <https://www.rfc-editor.org/info/rfc8439>. [RFC8547] Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E. Smith, "TCP-ENO: Encryption Negotiation Option", RFC 8547, DOI 10.17487/RFC8547, May 2019, <https://www.rfc-editor.org/info/rfc8547>.10.2. Informative References
[NIST-fail] Bernstein, D. and T. Lange, "Failures in NIST's ECC Standards", January 2016, <https://cr.yp.to/newelliptic/nistecc-20160106.pdf>. [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, <https://www.rfc-editor.org/info/rfc1122>. [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005, <https://www.rfc-editor.org/info/rfc4086>. [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, <https://www.rfc-editor.org/info/rfc7696>.
[tcpcrypt] Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D. Boneh, "The case for ubiquitous transport-level encryption", USENIX Security Symposium, August 2010. [TCPINC-API] Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres, D., and E. Smith, "Interface Extensions for TCP-ENO and tcpcrypt", Work in Progress, draft-ietf-tcpinc-api-06, June 2018.Acknowledgments
We are grateful for contributions, help, discussions, and feedback from the TCPINC Working Group and from other IETF reviewers, including Marcelo Bagnulo, David Black, Bob Briscoe, Jana Iyengar, Stephen Kent, Tero Kivinen, Mirja Kuhlewind, Yoav Nir, Christoph Paasch, Eric Rescorla, Kyle Rose, and Dale Worley. This work was funded by gifts from Intel (to Brad Karp) and from Google; by NSF award CNS-0716806 (A Clean-Slate Infrastructure for Information Flow Control); by DARPA CRASH under contract #N66001-10-2-4088; and by the Stanford Secure Internet of Things Project.Contributors
Dan Boneh and Michael Hamburg were coauthors of the draft that became this document.Authors' Addresses
Andrea Bittau Google 345 Spear Street San Francisco, CA 94105 United States of America Email: bittau@google.com
Daniel B. Giffin Stanford University 353 Serra Mall, Room 288 Stanford, CA 94305 United States of America Email: daniel@beech-grove.net Mark Handley University College London Gower St. London WC1E 6BT United Kingdom Email: M.Handley@cs.ucl.ac.uk David Mazieres Stanford University 353 Serra Mall, Room 290 Stanford, CA 94305 United States of America Email: dm@uun.org Quinn Slack Sourcegraph 121 2nd St Ste 200 San Francisco, CA 94105 United States of America Email: sqs@sourcegraph.com Eric W. Smith Kestrel Institute 3260 Hillview Avenue Palo Alto, CA 94304 United States of America Email: eric.smith@kestrel.edu