RFC 6216
Example Call Flows Using Session Initiation Protocol (SIP) Security Mechanisms
Pages: 67
Informational
Informational
Part 2 of 3 – Pages 15 to 34
4. Call Flow with S/MIME-Secured Message
4.1. MESSAGE Request with Signed Body
Below is an example of a signed message. The values on the Content- Type line (multipart/signed) and on the Content-Disposition line have been broken across lines to fit on the page, but they are not broken across lines in actual implementations. MESSAGE sip:kumiko@example.net SIP/2.0 <allOneLine> Via: SIP/2.0/TCP 192.0.2.2:15001; branch=z9hG4bK-d8754z-3a922b6dc0f0ff37-1---d8754z-; rport=50739 </allOneLine> Max-Forwards: 70 To: <sip:kumiko@example.net> From: <sip:fluffy@example.com>;tag=ef6bad5e Call-ID: N2NiZjI0NjRjNDQ0MTY1NDRjNWNmMGU1MDA2MDRhYmI. CSeq: 8473 MESSAGE <allOneLine> Accept: multipart/signed, text/plain, application/pkcs7-mime, application/sdp, multipart/alternative </allOneLine> <allOneLine> Content-Type: multipart/signed;boundary=3b515e121b43a911; micalg=sha1;protocol="application/pkcs7-signature" </allOneLine> Content-Length: 774 --3b515e121b43a911 Content-Type: text/plain Content-Transfer-Encoding: binary Hello! --3b515e121b43a911 Content-Type: application/pkcs7-signature;name=smime.p7s <allOneLine> Content-Disposition: attachment;handling=required; filename=smime.p7s </allOneLine> Content-Transfer-Encoding: binary ***************** * BINARY BLOB 1 * ***************** --3b515e121b43a911--
It is important to note that the signature ("BINARY BLOB 1") is
computed over the MIME headers and body, but excludes the multipart
boundary lines. The value on the Message-body line ends with CRLF.
The CRLF is included in the boundary and is not part of the signature
computation. To be clear, the signature is computed over data
starting with the "C" in the "Content-Type" and ending with the "!"
in the "Hello!".
Content-Type: text/plain
Content-Transfer-Encoding: binary
Hello!
Following is the ASN.1 parsing of encrypted contents referred to
above as "BINARY BLOB 1". Note that at address 30, the hash for the
signature is specified as SHA-1. Also note that the sender's
certificate is not attached as it is optional in [RFC5652].
0 472: SEQUENCE {
4 9: OBJECT IDENTIFIER signedData (1 2 840 113549 1 7 2)
15 457: [0] {
19 453: SEQUENCE {
23 1: INTEGER 1
26 11: SET {
28 9: SEQUENCE {
30 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
37 0: NULL
: }
: }
39 11: SEQUENCE {
41 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
: }
52 420: SET {
56 416: SEQUENCE {
60 1: INTEGER 1
63 125: SEQUENCE {
65 112: SEQUENCE {
67 11: SET {
69 9: SEQUENCE {
71 3: OBJECT IDENTIFIER countryName (2 5 4 6)
76 2: PrintableString 'US'
: }
: }
80 19: SET {
82 17: SEQUENCE {
84 3: OBJECT IDENTIFIER
: stateOrProvinceName (2 5 4 8)
89 10: UTF8String 'California'
: }
: }
101 17: SET {
103 15: SEQUENCE {
105 3: OBJECT IDENTIFIER localityName (2 5 4 7)
110 8: UTF8String 'San Jose'
: }
: }
120 14: SET {
122 12: SEQUENCE {
124 3: OBJECT IDENTIFIER
: organizationName (2 5 4 10)
129 5: UTF8String 'sipit'
: }
: }
136 41: SET {
138 39: SEQUENCE {
140 3: OBJECT IDENTIFIER
: organizationalUnitName (2 5 4 11)
145 32: UTF8String 'Sipit Test Certificate
Authority'
: }
: }
: }
179 9: INTEGER 00 96 A3 84 17 4E EF 8A 4D
: }
190 9: SEQUENCE {
192 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
199 0: NULL
: }
201 13: SEQUENCE {
203 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
214 0: NULL
: }
216 256: OCTET STRING
: 74 4D 21 39 D6 E2 E2 2C 30 5A AA BC 4E 60 8D 69
: A7 E5 79 50 1A B1 7D 4A D3 C1 03 9F 19 7D A2 76
: 97 B3 CE 30 CD 62 4B 96 20 35 DB C1 64 D9 33 92
: 96 CD 28 03 98 6E 2C 0C F6 8D 93 40 F2 88 DA 29
: AD 0B C2 0E F9 D3 6A 95 2C 79 6E C2 3D 62 E6 54
: A9 1B AC 66 DB 16 B7 44 6C 03 1B 71 9C EE C9 EC
: 4D 93 B1 CF F5 17 79 C5 C8 BA 2F A7 6C 4B DC CF
: 62 A3 F3 1A 1B 24 E4 40 66 3C 4F 87 86 BF 09 6A
: 7A 43 60 2B FC D8 3D 2B 57 17 CB 81 03 2A 56 69
: 81 82 FA 78 DE D2 3A 2F FA A3 C5 EA 8B E8 0C 36
: 1B BC DC FD 1B 8C 2E 0F 01 AF D9 E1 04 0E 4E 50
: 94 75 7C BD D9 0B DD AA FA 36 E3 EC E4 A5 35 46
: BE A2 97 1D AD BA 44 54 3A ED 94 DA 76 4A 51 BA
: A4 7D 7A 62 BF 2A 2F F2 5C 5A FE CA E6 B9 DC 5D
: EA 26 F2 35 17 19 20 CE 97 96 4E 72 9C 72 FD 1F
: 68 C1 6A 5C 86 42 F2 ED F2 70 65 4C C7 44 C5 7C
: }
: }
: }
: }
: }
SHA-1 parameters may be omitted entirely, instead of being set to
NULL, as mentioned in [RFC3370]. The above dump of Blob 1 has SHA-1
parameters set to NULL. Below are the same contents signed with the
same key, but omitting the NULL according to [RFC3370]. This is the
preferred encoding. This is covered in greater detail in Section 5.
0 468: SEQUENCE {
4 9: OBJECT IDENTIFIER signedData (1 2 840 113549 1 7 2)
15 453: [0] {
19 449: SEQUENCE {
23 1: INTEGER 1
26 9: SET {
28 7: SEQUENCE {
30 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
: }
: }
37 11: SEQUENCE {
39 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
: }
50 418: SET {
54 414: SEQUENCE {
58 1: INTEGER 1
61 125: SEQUENCE {
63 112: SEQUENCE {
65 11: SET {
67 9: SEQUENCE {
69 3: OBJECT IDENTIFIER countryName (2 5 4 6)
74 2: PrintableString 'US'
: }
: }
78 19: SET {
80 17: SEQUENCE {
82 3: OBJECT IDENTIFIER
: stateOrProvinceName (2 5 4 8)
87 10: UTF8String 'California'
: }
: }
99 17: SET {
101 15: SEQUENCE {
103 3: OBJECT IDENTIFIER localityName (2 5 4 7)
108 8: UTF8String 'San Jose'
: }
: }
118 14: SET {
120 12: SEQUENCE {
122 3: OBJECT IDENTIFIER
: organizationName (2 5 4 10)
127 5: UTF8String 'sipit'
: }
: }
134 41: SET {
136 39: SEQUENCE {
138 3: OBJECT IDENTIFIER
: organizationalUnitName (2 5 4 11)
143 32: UTF8String 'Sipit Test Certificate
Authority'
: }
: }
: }
177 9: INTEGER 00 96 A3 84 17 4E EF 8A 4D
: }
188 7: SEQUENCE {
190 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
: }
197 13: SEQUENCE {
199 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
210 0: NULL
: }
212 256: OCTET STRING
: 74 4D 21 39 D6 E2 E2 2C 30 5A AA BC 4E 60 8D 69
: A7 E5 79 50 1A B1 7D 4A D3 C1 03 9F 19 7D A2 76
: 97 B3 CE 30 CD 62 4B 96 20 35 DB C1 64 D9 33 92
: 96 CD 28 03 98 6E 2C 0C F6 8D 93 40 F2 88 DA 29
: AD 0B C2 0E F9 D3 6A 95 2C 79 6E C2 3D 62 E6 54
: A9 1B AC 66 DB 16 B7 44 6C 03 1B 71 9C EE C9 EC
: 4D 93 B1 CF F5 17 79 C5 C8 BA 2F A7 6C 4B DC CF
: 62 A3 F3 1A 1B 24 E4 40 66 3C 4F 87 86 BF 09 6A
: 7A 43 60 2B FC D8 3D 2B 57 17 CB 81 03 2A 56 69
: 81 82 FA 78 DE D2 3A 2F FA A3 C5 EA 8B E8 0C 36
: 1B BC DC FD 1B 8C 2E 0F 01 AF D9 E1 04 0E 4E 50
: 94 75 7C BD D9 0B DD AA FA 36 E3 EC E4 A5 35 46
: BE A2 97 1D AD BA 44 54 3A ED 94 DA 76 4A 51 BA
: A4 7D 7A 62 BF 2A 2F F2 5C 5A FE CA E6 B9 DC 5D
: EA 26 F2 35 17 19 20 CE 97 96 4E 72 9C 72 FD 1F
: 68 C1 6A 5C 86 42 F2 ED F2 70 65 4C C7 44 C5 7C
: }
: }
: }
: }
: }
4.2. MESSAGE Request with Encrypted Body
Below is an example of an encrypted text/plain message that says
"Hello!". The binary encrypted contents have been replaced with the
block "BINARY BLOB 2".
MESSAGE sip:kumiko@example.net SIP/2.0
<allOneLine>
Via: SIP/2.0/TCP 192.0.2.2:15001;
branch=z9hG4bK-d8754z-c276232b541dd527-1---d8754z-;
rport=50741
</allOneLine>
Max-Forwards: 70
To: <sip:kumiko@example.net>
From: <sip:fluffy@example.com>;tag=7a2e3025
Call-ID: MDYyMDhhODA3NWE2ZjEyYzAwOTZlMjExNWI2ZWQwZGM.
CSeq: 3260 MESSAGE
<allOneLine>
Accept: multipart/signed, text/plain, application/pkcs7-mime,
application/sdp, multipart/alternative
</allOneLine>
<allOneLine>
Content-Disposition: attachment;handling=required;
filename=smime.p7
</allOneLine>
Content-Transfer-Encoding: binary
<allOneLine>
Content-Type: application/pkcs7-mime;smime-type=enveloped-data;
name=smime.p7m
</allOneLine>
Content-Length: 565
*****************
* BINARY BLOB 2 *
*****************
Following is the ASN.1 parsing of "BINARY BLOB 2". Note that at
address 454, the encryption is set to aes128-CBC.
0 561: SEQUENCE {
4 9: OBJECT IDENTIFIER envelopedData (1 2 840 113549 1 7 3)
15 546: [0] {
19 542: SEQUENCE {
23 1: INTEGER 0
26 409: SET {
30 405: SEQUENCE {
34 1: INTEGER 0
37 125: SEQUENCE {
39 112: SEQUENCE {
41 11: SET {
43 9: SEQUENCE {
45 3: OBJECT IDENTIFIER countryName (2 5 4 6)
50 2: PrintableString 'US'
: }
: }
54 19: SET {
56 17: SEQUENCE {
58 3: OBJECT IDENTIFIER
: stateOrProvinceName (2 5 4 8)
63 10: UTF8String 'California'
: }
: }
75 17: SET {
77 15: SEQUENCE {
79 3: OBJECT IDENTIFIER localityName (2 5 4 7)
84 8: UTF8String 'San Jose'
: }
: }
94 14: SET {
96 12: SEQUENCE {
98 3: OBJECT IDENTIFIER
: organizationName (2 5 4 10)
103 5: UTF8String 'sipit'
: }
: }
110 41: SET {
112 39: SEQUENCE {
114 3: OBJECT IDENTIFIER
: organizationalUnitName (2 5 4 11)
119 32: UTF8String 'Sipit Test Certificate
Authority'
: }
: }
: }
153 9: INTEGER 00 96 A3 84 17 4E EF 8A 4E
: }
164 13: SEQUENCE {
166 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
177 0: NULL
: }
179 256: OCTET STRING
: B9 12 8F 32 AB 4A E2 38 C1 E0 53 69 88 D6 25 E7
: 40 03 B1 DE 79 21 A3 E8 23 5A 1B CB FB 58 F4 97
: 48 A7 C8 F0 3D DF 41 A3 5A 90 32 70 82 FA B0 DE
: D8 94 7C 6C 2E 01 FE 33 BD 62 CB 07 4F 58 DE 6F
: EA 3F EF B4 FB 46 72 58 9A 88 A0 85 BC 23 D7 C8
: 09 0B 90 8D 4A 5F 3F 96 7C AC D4 E2 19 E8 02 B6
: 0E F3 0D F2 91 4A 67 A9 EE 51 6A 97 D7 86 6D EC
: 78 6E C6 E0 83 7C E1 00 1F 5A 40 59 60 0C D7 EB
: A3 FB 04 B3 C9 A5 EB 79 ED B3 56 F8 F6 51 B2 5E
: 58 E2 D8 17 28 33 A6 B8 35 8C 0E 14 7F 90 D0 7B
: 03 00 6C 3D 81 29 F5 D7 E5 AC 75 5E E0 F0 DD E3
: 3E B2 06 97 D6 49 A9 CB 38 08 F1 84 05 F5 C0 BC
: 55 A6 D4 C9 D8 FD A4 AC 40 9F 9D 51 5B F7 3A C3
: C3 CD 3A E7 6D 21 05 D0 50 75 4F 14 D8 77 76 C6
: 13 A6 48 12 7B 25 CC 22 5D 73 BD 40 E4 15 02 A2
: 39 4A CB D9 55 08 A4 EE 4E 8A 5E BA C4 4A 46 9C
: }
: }
439 124: SEQUENCE {
441 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
452 29: SEQUENCE {
454 9: OBJECT IDENTIFIER
: aes128-CBC (2 16 840 1 101 3 4 1 2)
465 16: OCTET STRING
: CA 35 CA BD 1E 78 83 D9 20 6C 47 B9 9F DC 91 88
: }
483 80: [0]
: 1B AE 12 C4 0E 55 96 AB 99 CC 1C 7F B5 98 A4 BF
: D2 D8 7F 94 BB B5 38 05 59 F2 38 A1 CD 29 75 17
: 1D 63 1B 0B B0 2D 88 06 7F 78 80 F3 5A 3E DC 35
: BF 22 1E 03 32 59 98 DA FD 81 5F D9 41 63 3A 18
: FD B5 84 14 01 46 0B 40 EB 56 29 86 47 8B D1 EE
: }
: }
: }
: }
4.3. MESSAGE Request with Encrypted and Signed Body
In the example below, some of the header values have been split
across multiple lines. Where the lines have been broken, the
<allOneLine> convention has been used. This was only done to make it
fit in the RFC format. Specifically, the application/pkcs7-mime
Content-Type line is one line with no whitespace between the "mime;"
and the "smime-type". The values are split across lines for
formatting, but are not split in the real message. The binary
encrypted content has been replaced with "BINARY BLOB 3", and the
binary signed content has been replaced with "BINARY BLOB 4".
MESSAGE sip:kumiko@example.net SIP/2.0
<allOneLine>
Via: SIP/2.0/TCP 192.0.2.2:15001;
branch=z9hG4bK-d8754z-97a26e59b7262b34-1---d8754z-;
rport=50742
</allOneLine>
Max-Forwards: 70
To: <sip:kumiko@example.net>
From: <sip:fluffy@example.com>;tag=379f5b27
Call-ID: MjYwMzdjYTY3YWRkYzgzMjU0MGI4Mzc2Njk1YzJlNzE.
CSeq: 5449 MESSAGE
<allOneLine>
Accept: multipart/signed, text/plain, application/pkcs7-mime,
application/sdp, multipart/alternative
</allOneLine>
<allOneLine>
Content-Type: multipart/signed;boundary=e8df6e1ce5d1e864;
micalg=sha1;protocol="application/pkcs7-signature"
</allOneLine>
Content-Length: 1455
--e8df6e1ce5d1e864
<allOneLine>
Content-Type: application/pkcs7-mime;smime-type=enveloped-data;
name=smime.p7m
</allOneLine>
<allOneLine>
Content-Disposition: attachment;handling=required;
filename=smime.p7
</allOneLine>
Content-Transfer-Encoding: binary
*****************
* BINARY BLOB 3 *
*****************
--e8df6e1ce5d1e864
Content-Type: application/pkcs7-signature;name=smime.p7s
<allOneLine>
Content-Disposition: attachment;handling=required;
filename=smime.p7s
</allOneLine>
Content-Transfer-Encoding: binary
*****************
* BINARY BLOB 4 *
*****************
--e8df6e1ce5d1e864--
Below is the ASN.1 parsing of "BINARY BLOB 3".
0 561: SEQUENCE {
4 9: OBJECT IDENTIFIER envelopedData (1 2 840 113549 1 7 3)
15 546: [0] {
19 542: SEQUENCE {
23 1: INTEGER 0
26 409: SET {
30 405: SEQUENCE {
34 1: INTEGER 0
37 125: SEQUENCE {
39 112: SEQUENCE {
41 11: SET {
43 9: SEQUENCE {
45 3: OBJECT IDENTIFIER countryName (2 5 4 6)
50 2: PrintableString 'US'
: }
: }
54 19: SET {
56 17: SEQUENCE {
58 3: OBJECT IDENTIFIER
: stateOrProvinceName (2 5 4 8)
63 10: UTF8String 'California'
: }
: }
75 17: SET {
77 15: SEQUENCE {
79 3: OBJECT IDENTIFIER localityName (2 5 4 7)
84 8: UTF8String 'San Jose'
: }
: }
94 14: SET {
96 12: SEQUENCE {
98 3: OBJECT IDENTIFIER
: organizationName (2 5 4 10)
103 5: UTF8String 'sipit'
: }
: }
110 41: SET {
112 39: SEQUENCE {
114 3: OBJECT IDENTIFIER
: organizationalUnitName (2 5 4 11)
119 32: UTF8String 'Sipit Test Certificate
Authority'
: }
: }
: }
153 9: INTEGER 00 96 A3 84 17 4E EF 8A 4E
: }
164 13: SEQUENCE {
166 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
177 0: NULL
: }
179 256: OCTET STRING
: 49 11 0B 11 52 A9 9D E3 AA FB 86 CB EB 12 CC 8E
: 96 9D 85 3E 80 D2 7C C4 9B B7 81 4B B5 FA 13 80
: 6A 6A B2 34 72 D8 C0 82 60 DA B3 43 F8 51 8C 32
: 8B DD D0 76 6D 9C 46 73 C1 44 A0 10 FF 16 A4 83
: 74 85 21 74 7D E0 FD 42 C0 97 00 82 A2 80 81 22
: 9C A2 82 0A 85 F0 68 EF 9A D7 6D 1D 24 2B A9 5E
: B3 9A A0 3E A7 D9 1D 1C D7 42 CB 6F A5 81 66 23
: 28 00 7C 99 6A B6 03 3F 7E F6 48 EA 91 49 35 F1
: FD 40 54 5D AC F7 84 EA 3F 27 43 FD DE E2 10 DD
: 63 C4 35 4A 13 63 0B 6D 0D 9A D5 AB 72 39 69 8C
: 65 4C 44 C4 A3 31 60 79 B9 A8 A3 A1 03 FD 41 25
: 12 E5 F3 F8 47 CE 8C 42 D9 26 77 A5 57 AF 1A 95
: BF 05 A5 E9 47 F2 D1 AE DC 13 7E 1B 83 5C 8C C4
: 1F 31 BC 59 E6 FD 6E 9A B0 91 EC 71 A6 7F 28 3E
: 23 1B 40 E2 C0 60 CF 5E 5B 86 08 06 82 B4 B7 DB
: 00 DD AC 3A 39 27 E2 7C 96 AD 8A E9 C3 B8 06 5E
: }
: }
439 124: SEQUENCE {
441 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
452 29: SEQUENCE {
454 9: OBJECT IDENTIFIER
: aes128-CBC (2 16 840 1 101 3 4 1 2)
465 16: OCTET STRING
: 88 9B 13 75 A7 66 14 C3 CF CD C6 FF D2 91 5D A0
: }
483 80: [0]
: 80 0B A3 B7 57 89 B4 F4 70 AE 1D 14 A9 35 DD F9
: 1D 66 29 46 52 40 13 E1 3B 4A 23 E5 EC AB F9 35
: A6 B6 A4 BE C0 02 31 06 19 C4 39 22 7D 10 4C 0D
: F4 96 04 78 11 85 4E 7E E3 C3 BC B2 DF 55 17 79
: 5F F2 4E E5 25 42 37 45 39 5D F6 DA 57 9A 4E 0B
: }
: }
: }
: }
Below is the ASN.1 parsing of "BINARY BLOB 4".
0 472: SEQUENCE {
4 9: OBJECT IDENTIFIER signedData (1 2 840 113549 1 7 2)
15 457: [0] {
19 453: SEQUENCE {
23 1: INTEGER 1
26 11: SET {
28 9: SEQUENCE {
30 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
37 0: NULL
: }
: }
39 11: SEQUENCE {
41 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1)
: }
52 420: SET {
56 416: SEQUENCE {
60 1: INTEGER 1
63 125: SEQUENCE {
65 112: SEQUENCE {
67 11: SET {
69 9: SEQUENCE {
71 3: OBJECT IDENTIFIER countryName (2 5 4 6)
76 2: PrintableString 'US'
: }
: }
80 19: SET {
82 17: SEQUENCE {
84 3: OBJECT IDENTIFIER
: stateOrProvinceName (2 5 4 8)
89 10: UTF8String 'California'
: }
: }
101 17: SET {
103 15: SEQUENCE {
105 3: OBJECT IDENTIFIER localityName (2 5 4 7)
110 8: UTF8String 'San Jose'
: }
: }
120 14: SET {
122 12: SEQUENCE {
124 3: OBJECT IDENTIFIER
: organizationName (2 5 4 10)
129 5: UTF8String 'sipit'
: }
: }
136 41: SET {
138 39: SEQUENCE {
140 3: OBJECT IDENTIFIER
: organizationalUnitName (2 5 4 11)
145 32: UTF8String 'Sipit Test Certificate
Authority'
: }
: }
: }
179 9: INTEGER 00 96 A3 84 17 4E EF 8A 4D
: }
190 9: SEQUENCE {
192 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
199 0: NULL
: }
201 13: SEQUENCE {
203 9: OBJECT IDENTIFIER
: rsaEncryption (1 2 840 113549 1 1 1)
214 0: NULL
: }
216 256: OCTET STRING
: 6E 51 AC 24 2E BA 7C A1 EE 80 A8 55 BC D4 64 5D
: E5 29 09 5F B2 AF AA 6F 91 D2 97 79 32 5B AF CA
: FE A1 73 FC E5 57 4E C6 3B 67 35 AA E4 78 1E 59
: 93 EE 67 63 77 1E 7A 82 BC 1E 26 0F 39 75 0C A6
: 26 92 01 6A B7 5D F0 C0 2C 51 46 FB A7 36 44 E3
: 64 C6 11 CB 0B 6B FD F3 6D 7C FD 3E AE 2E 91 BB
: 78 9E F4 1B A1 20 68 B9 DE D3 E3 0C FC F7 14 9A
: 2C 64 AB 27 52 BD 52 EC 27 88 14 BD DB C3 54 C7
: EA 48 DB 07 E9 9B 2E C8 BE 62 A2 76 83 53 37 E8
: 02 4B D1 86 E9 DF 2E BD 93 39 EC 2F 01 53 A0 7F
: 1A B9 A6 31 FC E7 91 1C DB 22 4A 67 83 94 B2 4E
: 28 A9 CD DE 4A 04 6A E0 86 90 7B 58 5F DB 7A 96
: 96 A0 25 61 C2 58 A2 28 E5 B3 B2 F1 6D 51 06 9C
: 78 61 0D D8 3A A7 9F A3 B5 87 0B 80 11 C2 A9 1A
: E5 17 1C EB 82 55 AB CD 04 E7 D9 5B 11 E8 B7 47
: FE FD CC B7 DB 47 6F 77 85 9E 24 D8 11 E1 E4 7D
: }
: }
: }
: }
: }
5. Observed Interoperability Issues
This section describes some common interoperability problems. These
were observed by the authors at SIPit interoperability events.
Implementers should be careful to verify that their systems do not
introduce these common problems, and, when possible, make their
clients forgiving in what they receive. Implementations should take extra care to produce reasonable error messages when interacting with software that has these problems. Some SIP clients incorrectly only do SSLv3 and do not support TLS. See Section 26.2.1 of [RFC3261]. Many SIP clients were found to accept expired certificates with no warning or error. See Section 4.1.2.5 of [RFC5280]. When used with SIP, TLS and S/MIME provide the identity of the peer that a client is communicating with in the Subject Alternative Name in the certificate. The software checks that this name corresponds to the identity the server is trying to contact. Normative text describing path validation can be found in Section 7 of [RFC5922] and Section 6 of [RFC5280]. If a client is trying to set up a TLS connection to good.example.com and it gets a TLS connection set up with a server that presents a valid certificate but with the name evil.example.com, it will typically generate an error or warning of some type. Similarly with S/MIME, if a user is trying to communicate with sip:fluffy@example.com, one of the items in the Subject Alternate Name set in the certificate will need to match according to the certificate validation rules in Section 23 of [RFC3261] and Section 6 of [RFC5280]. Some implementations used binary MIME encodings while others used base64. It is advisable that implementations send only binary and are prepared to receive either. See Section 3.2 of [RFC5621]. In several places in this document, the messages contain the encoding for the SHA-1 digest algorithm identifier. The preferred form for encoding as set out in Section 2 of [RFC3370] is the form in which the optional AlgorithmIdentifier parameter field is omitted. However, [RFC3370] also says the recipients need to be able to receive the form in which the AlgorithmIdentifier parameter field is present and set to NULL. Examples of the form using NULL can be found in Section 4.2 of [RFC4134]. Receivers really do need to be able to receive the form that includes the NULL because the NULL form, while not preferred, is what was observed as being generated by most implementations. Implementers should also note that if the algorithm is MD5 instead of SHA-1, then the form that omits the AlgorithmIdentifier parameters field is not allowed and the sender has to use the form where the NULL is included. The preferred encryption algorithm for S/MIME in SIP is AES as defined in [RFC3853].
Observed S/MIME interoperability has been better when UAs did not attach the senders' certificates. Attaching the certificates significantly increases the size of the messages, which should be considered when sending over UDP. Furthermore, the receiver cannot rely on the sender to always send the certificate, so it does not turn out to be useful in most situations. Please note that the certificate path validation algorithm described in Section 6 of [RFC5280] is a complex algorithm for which all of the details matter. There are numerous ways in which failing to precisely implement the algorithm as specified in Section 6 of [RFC5280] can create a security flaw, a simple example of which is the failure to check the expiration date that is already mentioned above. It is important for developers to ensure that this validation is performed and that the results are verified by their applications or any libraries that they use.6. Additional Test Scenarios
This section provides a non-exhaustive list of tests that implementations should perform while developing systems that use S/MIME and TLS for SIP. Much of the required behavior for inspecting certificates when using S/MIME and TLS with SIP is currently underspecified. The non- normative recommendations in this document capture the current folklore around that required behavior, guided by both related normative works such as [RFC4474] (particularly, Section 13.4 Domain Names and Subordination) and informative works such as [RFC2818], Section 3.1. To summarize, test plans should: o For S/MIME secured bodies, ensure that the peer's URI (address-of- record, as per [RFC3261], Section 23.3) appears in the subjectAltName of the peer's certificate as a uniformResourceIdentifier field. o For TLS, ensure that the peer's hostname appears as described in [RFC5922]. Also: * ensure an exact match in a dNSName entry in the subjectAltName if there are any dNSNames in the subjectAltName. Wildcard matching is not allowed against these dNSName entries. See Section 7.1 of [RFC5922]. * ensure that the most specific CommonName in the Subject field matches if there are no dNSName entries in the subjectAltName at all (which is not the same as there being no matching
dNSName entries). This match can be either exact, or against
an entry that uses the wildcard matching character '*'.
The peer's hostname is discovered from the initial DNS query in
the server location process [RFC3263].
o IP addresses can appear in subjectAltName ([RFC5280]) of the
peer's certificate, e.g., "IP:192.168.0.1". Note that if IP
addresses are used in subjectAltName, there are important
ramifications regarding the use of Record-Route headers that also
need to be considered. See Section 7.5 of [RFC5922]. Use of IP
addresses instead of domain names is inadvisable.
For each of these tests, an implementation will proceed past the
verification point only if the certificate is "good". S/MIME
protected requests presenting bad certificate data will be rejected.
S/MIME protected responses presenting bad certificate information
will be ignored. TLS connections involving bad certificate data will
not be completed.
1. S/MIME : Good peer certificate
2. S/MIME : Bad peer certificate (peer URI does not appear in
subjectAltName)
3. S/MIME : Bad peer certificate (valid authority chain does not
end at a trusted CA)
4. S/MIME : Bad peer certificate (incomplete authority chain)
5. S/MIME : Bad peer certificate (the current time does not fall
within the period of validity)
6. S/MIME : Bad peer certificate (certificate, or certificate in
authority chain, has been revoked)
7. S/MIME : Bad peer certificate ("Digital Signature" is not
specified as an X509v3 Key Usage)
8. TLS : Good peer certificate (hostname appears in dNSName in
subjectAltName)
9. TLS : Good peer certificate (no dNSNames in subjectAltName,
hostname appears in Common Name (CN) of Subject)
10. TLS : Good peer certificate (CN of Subject empty, and
subjectAltName extension contains an iPAddress stored in the
octet string in network byte order form as specified in RFC 791
[RFC0791])
11. TLS : Bad peer certificate (no match in dNSNames or in the
Subject CN)
12. TLS : Bad peer certificate (valid authority chain does not end
at a trusted CA)
13. TLS : Bad peer certificate (incomplete authority chain)
14. TLS : Bad peer certificate (the current time does not fall
within the period of validity)
15. TLS : Bad peer certificate (certificate, or certificate in
authority chain, has been revoked)
16. TLS : Bad peer certificate ("TLS Web Server Authentication" is
not specified as an X509v3 Key Usage)
17. TLS : Bad peer certificate (Neither "SIP Domain" nor "Any
Extended Key Usage" specified as an X509v3 Extended Key Usage,
and X509v3 Extended Key Usage is present)
7. Acknowledgments
Many thanks to the developers of all the open source software used to
create these call flows. This includes the underlying crypto and TLS
software used from openssl.org, the SIP stack from
www.resiprocate.org, and the SIP for Instant Messaging and Presence
Leveraging Extensions (SIMPLE) Instant Messaging and Presence
Protocol (IMPP) agent from www.sipimp.org. The TLS flow dumps were
done with SSLDump from http://www.rtfm.com/ssldump. The book "SSL
and TLS" [EKR-TLS] was a huge help in developing the code for these
flows. It's sad there is no second edition.
Thanks to Jim Schaad, Russ Housley, Eric Rescorla, Dan Wing, Tat
Chan, and Lyndsay Campbell, who all helped find and correct mistakes
in this document.
Vijay Gurbani and Alan Jeffrey contributed much of the additional
test scenario content.
8. Security Considerations
Implementers must never use any of the certificates provided in this document in anything but a test environment. Installing the CA root certificates used in this document as a trusted root in operational software would completely destroy the security of the system while giving the user the impression that the system was operating securely. This document recommends some things that implementers might test or verify to improve the security of their implementations. It is impossible to make a comprehensive list of these, and this document only suggests some of the most common mistakes that have been seen at the SIPit interoperability events. Just because an implementation does everything this document recommends does not make it secure. This document does not show any messages to check certificate revocation status (see Sections 3.3 and 6.3 of [RFC5280]) as that is not part of the SIP call flow. The expectation is that revocation status is checked regularly to protect against the possibility of certificate compromise or repudiation. For more information on how certificate revocation status can be checked, see [RFC2560] (Online Certificate Status Protocol) and [RFC5055] (Server-Based Certificate Validation Protocol).9. References
9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP", RFC 2560, June 1999. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, June 2002. [RFC3370] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms", RFC 3370, August 2002.
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [RFC3853] Peterson, J., "S/MIME Advanced Encryption Standard (AES) Requirement for the Session Initiation Protocol (SIP)", RFC 3853, July 2004. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC5055] Freeman, T., Housley, R., Malpani, A., Cooper, D., and W. Polk, "Server-Based Certificate Validation Protocol (SCVP)", RFC 5055, December 2007. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [RFC5621] Camarillo, G., "Message Body Handling in the Session Initiation Protocol (SIP)", RFC 5621, September 2009. [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, September 2009. [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010. [RFC5922] Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain Certificates in the Session Initiation Protocol (SIP)", RFC 5922, June 2010. [RFC5923] Gurbani, V., Mahy, R., and B. Tate, "Connection Reuse in the Session Initiation Protocol (SIP)", RFC 5923, June 2010.
[RFC5924] Lawrence, S. and V. Gurbani, "Extended Key Usage (EKU) for Session Initiation Protocol (SIP) X.509 Certificates", RFC 5924, June 2010. [X.509] International Telecommunications Union, "Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks", ITU-T Recommendation X.509 (2005), ISO/ IEC 9594-8:2005. [X.683] International Telecommunications Union, "Information technology - Abstract Syntax Notation One (ASN.1): Parameterization of ASN.1 specifications", ITU-T Recommendation X.683 (2002), ISO/IEC 8824-4:2002, 2002.9.2. Informative References
[EKR-TLS] Rescorla, E., "SSL and TLS - Designing and Building Secure Systems", Addison-Wesley, ISBN 0-201-61598-3, 2001. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC4134] Hoffman, P., "Examples of S/MIME Messages", RFC 4134, July 2005. [RFC4475] Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J., and H. Schulzrinne, "Session Initiation Protocol (SIP) Torture Test Messages", RFC 4475, May 2006. [RFC4514] Zeilenga, K., "Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names", RFC 4514, June 2006. [ssldump-manpage] Rescorla, E., "SSLDump manpage", <http://www.rtfm.com/ssldump/Ssldump.html>.
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