tsvwg Douglas Otis
Internet Draft SANlight
Document: draft-otis-sctp-digest-01.txt June 4, 2001
Category: Standards Track
Integrity-Authentication Digest for SCTP
draft-otis-sctp-digest-01.txt
1 Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
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2 Abstract
This document describes the inclusion of a digest within the SCTP
[RFC2960] packet. This digest is negotiated on a per Association
basis. The means of negotiation and use is beyond the scope of
this document.
3 Integrity-Authentication Digest
This chunk is used to verify integrity a SCTP packet. This chunk is
placed as the first chunk within the SCTP packet. This removes the
Checksum value from the common header.
The common header changes to:
SCTP Common Header Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port Number | Destination Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
D. Otis <draft-otis-sctp-digest-01.txt> 2
The digest is created over the entire SCTP packet with the Digest
Value zeroed. To assist generalized processing, an IANA Designator
for the type of digest algorithm used is placed within the Chunk Flag
region. The calculated Digest Value then replaces this zeroed
region. The format of the IA-Digest chunk is shown below:
ID Value Chunk Type
----- ----------
0x80 - Integrity-Authentication (IA-Digest)
Integrity-Authentication Digest
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 0x80 |IANA Designator| Digest Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Digest Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fletcher-16
Modulo 65535 Fletcher 32 bit checksum. Both one's complement 16 bit
summations are limited to modulo 65535 or 2^16 - 1. This
modification greatly improves the ability to detect a stuck bit.
CRC-32c
This Cyclic Redundancy Check is reflected to accommodate the bit
order of Ethernet. The initial CRC values are set to all ones to
improve a zero header condition. The final result is then inverted
before being stored.
D. Otis <draft-otis-sctp-digest-01.txt> 3
/* Digest Designators */
#define NO_CHECK 1
#define FLETCHER 2
#define CRC 3
/* Packet Offsets */
#define IA_CHUNK_TYPE 8
#define IA_DESIGNATOR 9
#define IA_DIGEST_B3 12
#define IA_DIGEST_B2 13
#define IA_DIGEST_B1 14
#define IA_DIGEST_B0 15
/* generated using (0x11EDC6F41)
x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+x^19+x^18+x^14+x^13+
x^11+x^10+x^9+x^8+x^6+1
*/
unsigned long crctab[256] =
{
0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
D. Otis <draft-otis-sctp-digest-01.txt> 4
0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
};
#define CRC32(crc, d) (crc=(crc>>8)^crctab[(crc^(d))&0xff])
/* fscgen generates the digest based on Digest Designator */
/* buf[] contains the SCTP packet */
/* length is the packet length including padding */
int
fscgen(unsigned char buf[], int length)
{
int i = 0;
unsigned int s1 = 0;
unsigned int s2 = 0;
unsigned int crc = ~0;
if (buf[IA_CHUNK_TYPE] != 0x80)
return (-1);
switch (buf[IA_DESIGNATOR])
D. Otis <draft-otis-sctp-digest-01.txt> 5
{
case FLETCHER:
while (i < length)
{
s1+= (buf[i] << 8) + buf[i+1];
if (s1 >= 0xFFFF)
s1 -= 0xFFFF;
s2+=s1;
if (s2 >= 0xFFFF)
s2 -= 0xFFFF;
i+=2;
}
buf[IA_DIGEST_B3] = s2 >> 8;
buf[IA_DIGEST_B2] = s2 & 0xFF;
buf[IA_DIGEST_B1] = s1 >> 8;
buf[IA_DIGEST_B0] = s1 & 0xFF;
break;
case CRC:
while (i < length)
CRC32 (crc, buf[i++]); /* assumes digest zeroed */
crc^=0xFFFFFFFF;
buf[IA_DIGEST_B3] = crc >> 24;
buf[IA_DIGEST_B2] = (crc >> 16) & 0xFF;
buf[IA_DIGEST_B1] = (crc >> 8) & 0xFF;
buf[IA_DIGEST_B0] = crc & 0xFF;
break;
case NO_CHECK:
break;
default:
break;
}
return (0);
}
/* fscchk verifies the digest based on Digest Designator */
/* buf[] contains the SCTP packet */
/* length is the packet length including padding */
int
fscchk(unsigned char buf[], int length)
{
int i = 0;
unsigned int sav_s1;
unsigned int sav_s2;
unsigned int sav_crc;
unsigned int s1 = 0;
unsigned int s2 = 0;
unsigned int crc = ~0;
if (buf[IA_CHUNK_TYPE] != 0x80)
D. Otis <draft-otis-sctp-digest-01.txt> 6
return (-1);
switch (buf[IA_DESIGNATOR])
{
case FLETCHER:
sav_s2 = (buf[IA_DIGEST_B3] << 8) + buf[IA_DIGEST_B2];
sav_s1 = (buf[IA_DIGEST_B1] << 8) + buf[IA_DIGEST_B0];
buf[IA_DIGEST_B3] = buf[IA_DIGEST_B2] = \
buf[IA_DIGEST_B1] = buf[IA_DIGEST_B0] = 0;
while (i < length)
{
s1+= (buf[i] << 8) + buf[i+1];
if (s1 >= 0xFFFF)
s1 -= 0xFFFF;
s2+=s1;
if (s2 >= 0xFFFF)
s2 -= 0xFFFF;
i+=2;
}
if (sav_s2 != s2 || sav_s1 != s1)
return(-1);
break;
case CRC:
sav_crc = (buf[IA_DIGEST_B3]<<24)+ \
(buf[IA_DIGEST_B2]<<16)+ \
(buf[IA_DIGEST_B1]<<8)+ \
buf[IA_DIGEST_B0];
buf[IA_DIGEST_B3] = buf[IA_DIGEST_B2] = \
buf[IA_DIGEST_B1] = buf[IA_DIGEST_B0] = 0;
while (i < length)
CRC32 (crc, buf[i++]); /* assumes digest zeroed */
crc^=0xFFFFFFFF;
if (crc != sav_crc)
return (-1);
break;
case NO_CHECK:
break;
default:
break;
}
return (0);
}
D. Otis <draft-otis-sctp-digest-01.txt> 7
Editor's Note:
The IANA Designator for SCTP Integrity-Authentication Digest
Number Description Reference
--------- ------------------------------ ---------
0 Reserved
1 No Digest (No Digest Value)
2 Modulo 65535 Fletcher 32 bit Digest
3 CRC-32c Digest(Castagnioli93)
4 KRB5_MD5 [RFC1964]
5 KRB5_DES_MD5 [RFC1964]
6 KRB5_DES_MAC [RFC1964]
7 SPKM [RFC2025]
8 SHA-1 [RFC2404]
9 - 239 Reserved by the IANA
240 - 254 Reserved for Private algorithms
255 Reserved
[Castagnoli93] Guy Castagnoli, Stefan Braeuer and Martin
Herrman "Optimization of Cyclic Redundancy-Check Codes with 24
and 32 Parity Bits", IEEE Transactions on Communications, Vol. 41,
No. 6, June 1993
[FIPS-180-1] NIST, FIPS PUB 180-1: Secure Hash Standard,
April 1995.
http://csrc.nist.gov/fips/fip180-1.txt (ascii)
http://csrc.nist.gov/fips/fip180-1.ps (postscript)
D. Otis <draft-otis-sctp-digest-01.txt> 8
Author's Addresses
Douglas Otis
SANlight Inc.
160 Saratoga Ave. #40
Santa Clara, CA 95051
Phone: 408-260-1400 x 2
Email: dotis@sanlight.net
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