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Re: [incremental] Patch: FYI: add missing bits to checksum
Paolo> You cannot find a
Paolo> second pre-image for MD5, but you can find collisions pretty easily,
Paolo> so it could yield security problems (no I'm not exaggerating it *too
Paolo> much*---they would be wrong-code bugs, but if somebody plays with MD5
Paolo> collisions you can assume that they are doing something malicious).
I have thought about this argument before. I am not really convinced
by it.
Frankly, neither am I. It's not going to be Ken Thompson's attack for
the 3rd millennium. But I would find it less worrisome to not have it,
rather than to know about it.
I attach a SHA1 from glibc with a similar interface to MD5.
I tried to see this problem in action, but I was unable. The only MD5
collision I could easily find yields a program that is rejected by the
lexer. If you have a "nice" collision, I'd like to have it.
It's easier to just find a MD5-collision generator and run it until it
works. But I think you have to be sure that the hash has processed a
full block before it is fed the string.
Paolo
/* Declarations of functions and data types used for SHA1 sum
library functions.
Copyright (C) 2000, 2001, 2003, 2005, 2006 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
#ifndef SHA1_H
# define SHA1_H 1
# include <stdio.h>
# include <stdint.h>
/* Structure to save state of computation between the single steps. */
struct sha1_ctx
{
uint32_t A;
uint32_t B;
uint32_t C;
uint32_t D;
uint32_t E;
uint32_t total[2];
uint32_t buflen;
uint32_t buffer[32];
};
/* Initialize structure containing state of computation. */
extern void sha1_init_ctx (struct sha1_ctx *ctx);
/* Starting with the result of former calls of this function (or the
initialization function update the context for the next LEN bytes
starting at BUFFER.
It is necessary that LEN is a multiple of 64!!! */
extern void sha1_process_block (const void *buffer, size_t len,
struct sha1_ctx *ctx);
/* Starting with the result of former calls of this function (or the
initialization function update the context for the next LEN bytes
starting at BUFFER.
It is NOT required that LEN is a multiple of 64. */
extern void sha1_process_bytes (const void *buffer, size_t len,
struct sha1_ctx *ctx);
/* Process the remaining bytes in the buffer and put result from CTX
in first 20 bytes following RESBUF. The result is always in little
endian byte order, so that a byte-wise output yields to the wanted
ASCII representation of the message digest.
IMPORTANT: On some systems it is required that RESBUF be correctly
aligned for a 32 bits value. */
extern void *sha1_finish_ctx (struct sha1_ctx *ctx, void *resbuf);
/* Put result from CTX in first 20 bytes following RESBUF. The result is
always in little endian byte order, so that a byte-wise output yields
to the wanted ASCII representation of the message digest.
IMPORTANT: On some systems it is required that RESBUF is correctly
aligned for a 32 bits value. */
extern void *sha1_read_ctx (const struct sha1_ctx *ctx, void *resbuf);
/* Compute SHA1 message digest for bytes read from STREAM. The
resulting message digest number will be written into the 20 bytes
beginning at RESBLOCK. */
extern int sha1_stream (FILE *stream, void *resblock);
/* Compute SHA1 message digest for LEN bytes beginning at BUFFER. The
result is always in little endian byte order, so that a byte-wise
output yields to the wanted ASCII representation of the message
digest. */
extern void *sha1_buffer (const char *buffer, size_t len, void *resblock);
#endif
/* sha1.c - Functions to compute SHA1 message digest of files or
memory blocks according to the NIST specification FIPS-180-1.
Copyright (C) 2000, 2001, 2003, 2004, 2005, 2006 Free Software
Foundation, Inc.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
/* Written by Scott G. Miller
Credits:
Robert Klep <robert@ilse.nl> -- Expansion function fix
*/
#include <config.h>
#include "sha1.h"
#include <stddef.h>
#include <string.h>
#if USE_UNLOCKED_IO
# include "unlocked-io.h"
#endif
#ifdef WORDS_BIGENDIAN
# define SWAP(n) (n)
#else
# define SWAP(n) \
(((n) << 24) | (((n) & 0xff00) << 8) | (((n) >> 8) & 0xff00) | ((n) >> 24))
#endif
#define BLOCKSIZE 4096
#if BLOCKSIZE % 64 != 0
# error "invalid BLOCKSIZE"
#endif
/* This array contains the bytes used to pad the buffer to the next
64-byte boundary. (RFC 1321, 3.1: Step 1) */
static const unsigned char fillbuf[64] = { 0x80, 0 /* , 0, 0, ... */ };
/* Take a pointer to a 160 bit block of data (five 32 bit ints) and
initialize it to the start constants of the SHA1 algorithm. This
must be called before using hash in the call to sha1_hash. */
void
sha1_init_ctx (struct sha1_ctx *ctx)
{
ctx->A = 0x67452301;
ctx->B = 0xefcdab89;
ctx->C = 0x98badcfe;
ctx->D = 0x10325476;
ctx->E = 0xc3d2e1f0;
ctx->total[0] = ctx->total[1] = 0;
ctx->buflen = 0;
}
/* Put result from CTX in first 20 bytes following RESBUF. The result
must be in little endian byte order.
IMPORTANT: On some systems it is required that RESBUF is correctly
aligned for a 32-bit value. */
void *
sha1_read_ctx (const struct sha1_ctx *ctx, void *resbuf)
{
((uint32_t *) resbuf)[0] = SWAP (ctx->A);
((uint32_t *) resbuf)[1] = SWAP (ctx->B);
((uint32_t *) resbuf)[2] = SWAP (ctx->C);
((uint32_t *) resbuf)[3] = SWAP (ctx->D);
((uint32_t *) resbuf)[4] = SWAP (ctx->E);
return resbuf;
}
/* Process the remaining bytes in the internal buffer and the usual
prolog according to the standard and write the result to RESBUF.
IMPORTANT: On some systems it is required that RESBUF is correctly
aligned for a 32-bit value. */
void *
sha1_finish_ctx (struct sha1_ctx *ctx, void *resbuf)
{
/* Take yet unprocessed bytes into account. */
uint32_t bytes = ctx->buflen;
size_t size = (bytes < 56) ? 64 / 4 : 64 * 2 / 4;
/* Now count remaining bytes. */
ctx->total[0] += bytes;
if (ctx->total[0] < bytes)
++ctx->total[1];
/* Put the 64-bit file length in *bits* at the end of the buffer. */
ctx->buffer[size - 2] = SWAP ((ctx->total[1] << 3) | (ctx->total[0] >> 29));
ctx->buffer[size - 1] = SWAP (ctx->total[0] << 3);
memcpy (&((char *) ctx->buffer)[bytes], fillbuf, (size - 2) * 4 - bytes);
/* Process last bytes. */
sha1_process_block (ctx->buffer, size * 4, ctx);
return sha1_read_ctx (ctx, resbuf);
}
/* Compute SHA1 message digest for bytes read from STREAM. The
resulting message digest number will be written into the 16 bytes
beginning at RESBLOCK. */
int
sha1_stream (FILE *stream, void *resblock)
{
struct sha1_ctx ctx;
char buffer[BLOCKSIZE + 72];
size_t sum;
/* Initialize the computation context. */
sha1_init_ctx (&ctx);
/* Iterate over full file contents. */
while (1)
{
/* We read the file in blocks of BLOCKSIZE bytes. One call of the
computation function processes the whole buffer so that with the
next round of the loop another block can be read. */
size_t n;
sum = 0;
/* Read block. Take care for partial reads. */
while (1)
{
n = fread (buffer + sum, 1, BLOCKSIZE - sum, stream);
sum += n;
if (sum == BLOCKSIZE)
break;
if (n == 0)
{
/* Check for the error flag IFF N == 0, so that we don't
exit the loop after a partial read due to e.g., EAGAIN
or EWOULDBLOCK. */
if (ferror (stream))
return 1;
goto process_partial_block;
}
/* We've read at least one byte, so ignore errors. But always
check for EOF, since feof may be true even though N > 0.
Otherwise, we could end up calling fread after EOF. */
if (feof (stream))
goto process_partial_block;
}
/* Process buffer with BLOCKSIZE bytes. Note that
BLOCKSIZE % 64 == 0
*/
sha1_process_block (buffer, BLOCKSIZE, &ctx);
}
process_partial_block:;
/* Process any remaining bytes. */
if (sum > 0)
sha1_process_bytes (buffer, sum, &ctx);
/* Construct result in desired memory. */
sha1_finish_ctx (&ctx, resblock);
return 0;
}
/* Compute SHA1 message digest for LEN bytes beginning at BUFFER. The
result is always in little endian byte order, so that a byte-wise
output yields to the wanted ASCII representation of the message
digest. */
void *
sha1_buffer (const char *buffer, size_t len, void *resblock)
{
struct sha1_ctx ctx;
/* Initialize the computation context. */
sha1_init_ctx (&ctx);
/* Process whole buffer but last len % 64 bytes. */
sha1_process_bytes (buffer, len, &ctx);
/* Put result in desired memory area. */
return sha1_finish_ctx (&ctx, resblock);
}
void
sha1_process_bytes (const void *buffer, size_t len, struct sha1_ctx *ctx)
{
/* When we already have some bits in our internal buffer concatenate
both inputs first. */
if (ctx->buflen != 0)
{
size_t left_over = ctx->buflen;
size_t add = 128 - left_over > len ? len : 128 - left_over;
memcpy (&((char *) ctx->buffer)[left_over], buffer, add);
ctx->buflen += add;
if (ctx->buflen > 64)
{
sha1_process_block (ctx->buffer, ctx->buflen & ~63, ctx);
ctx->buflen &= 63;
/* The regions in the following copy operation cannot overlap. */
memcpy (ctx->buffer,
&((char *) ctx->buffer)[(left_over + add) & ~63],
ctx->buflen);
}
buffer = (const char *) buffer + add;
len -= add;
}
/* Process available complete blocks. */
if (len >= 64)
{
#if !_STRING_ARCH_unaligned
# define alignof(type) offsetof (struct { char c; type x; }, x)
# define UNALIGNED_P(p) (((size_t) p) % alignof (uint32_t) != 0)
if (UNALIGNED_P (buffer))
while (len > 64)
{
sha1_process_block (memcpy (ctx->buffer, buffer, 64), 64, ctx);
buffer = (const char *) buffer + 64;
len -= 64;
}
else
#endif
{
sha1_process_block (buffer, len & ~63, ctx);
buffer = (const char *) buffer + (len & ~63);
len &= 63;
}
}
/* Move remaining bytes in internal buffer. */
if (len > 0)
{
size_t left_over = ctx->buflen;
memcpy (&((char *) ctx->buffer)[left_over], buffer, len);
left_over += len;
if (left_over >= 64)
{
sha1_process_block (ctx->buffer, 64, ctx);
left_over -= 64;
memcpy (ctx->buffer, &ctx->buffer[16], left_over);
}
ctx->buflen = left_over;
}
}
/* --- Code below is the primary difference between md5.c and sha1.c --- */
/* SHA1 round constants */
#define K1 0x5a827999
#define K2 0x6ed9eba1
#define K3 0x8f1bbcdc
#define K4 0xca62c1d6
/* Round functions. Note that F2 is the same as F4. */
#define F1(B,C,D) ( D ^ ( B & ( C ^ D ) ) )
#define F2(B,C,D) (B ^ C ^ D)
#define F3(B,C,D) ( ( B & C ) | ( D & ( B | C ) ) )
#define F4(B,C,D) (B ^ C ^ D)
/* Process LEN bytes of BUFFER, accumulating context into CTX.
It is assumed that LEN % 64 == 0.
Most of this code comes from GnuPG's cipher/sha1.c. */
void
sha1_process_block (const void *buffer, size_t len, struct sha1_ctx *ctx)
{
const uint32_t *words = buffer;
size_t nwords = len / sizeof (uint32_t);
const uint32_t *endp = words + nwords;
uint32_t x[16];
uint32_t a = ctx->A;
uint32_t b = ctx->B;
uint32_t c = ctx->C;
uint32_t d = ctx->D;
uint32_t e = ctx->E;
/* First increment the byte count. RFC 1321 specifies the possible
length of the file up to 2^64 bits. Here we only compute the
number of bytes. Do a double word increment. */
ctx->total[0] += len;
if (ctx->total[0] < len)
++ctx->total[1];
#define rol(x, n) (((x) << (n)) | ((uint32_t) (x) >> (32 - (n))))
#define M(I) ( tm = x[I&0x0f] ^ x[(I-14)&0x0f] \
^ x[(I-8)&0x0f] ^ x[(I-3)&0x0f] \
, (x[I&0x0f] = rol(tm, 1)) )
#define R(A,B,C,D,E,F,K,M) do { E += rol( A, 5 ) \
+ F( B, C, D ) \
+ K \
+ M; \
B = rol( B, 30 ); \
} while(0)
while (words < endp)
{
uint32_t tm;
int t;
for (t = 0; t < 16; t++)
{
x[t] = SWAP (*words);
words++;
}
R( a, b, c, d, e, F1, K1, x[ 0] );
R( e, a, b, c, d, F1, K1, x[ 1] );
R( d, e, a, b, c, F1, K1, x[ 2] );
R( c, d, e, a, b, F1, K1, x[ 3] );
R( b, c, d, e, a, F1, K1, x[ 4] );
R( a, b, c, d, e, F1, K1, x[ 5] );
R( e, a, b, c, d, F1, K1, x[ 6] );
R( d, e, a, b, c, F1, K1, x[ 7] );
R( c, d, e, a, b, F1, K1, x[ 8] );
R( b, c, d, e, a, F1, K1, x[ 9] );
R( a, b, c, d, e, F1, K1, x[10] );
R( e, a, b, c, d, F1, K1, x[11] );
R( d, e, a, b, c, F1, K1, x[12] );
R( c, d, e, a, b, F1, K1, x[13] );
R( b, c, d, e, a, F1, K1, x[14] );
R( a, b, c, d, e, F1, K1, x[15] );
R( e, a, b, c, d, F1, K1, M(16) );
R( d, e, a, b, c, F1, K1, M(17) );
R( c, d, e, a, b, F1, K1, M(18) );
R( b, c, d, e, a, F1, K1, M(19) );
R( a, b, c, d, e, F2, K2, M(20) );
R( e, a, b, c, d, F2, K2, M(21) );
R( d, e, a, b, c, F2, K2, M(22) );
R( c, d, e, a, b, F2, K2, M(23) );
R( b, c, d, e, a, F2, K2, M(24) );
R( a, b, c, d, e, F2, K2, M(25) );
R( e, a, b, c, d, F2, K2, M(26) );
R( d, e, a, b, c, F2, K2, M(27) );
R( c, d, e, a, b, F2, K2, M(28) );
R( b, c, d, e, a, F2, K2, M(29) );
R( a, b, c, d, e, F2, K2, M(30) );
R( e, a, b, c, d, F2, K2, M(31) );
R( d, e, a, b, c, F2, K2, M(32) );
R( c, d, e, a, b, F2, K2, M(33) );
R( b, c, d, e, a, F2, K2, M(34) );
R( a, b, c, d, e, F2, K2, M(35) );
R( e, a, b, c, d, F2, K2, M(36) );
R( d, e, a, b, c, F2, K2, M(37) );
R( c, d, e, a, b, F2, K2, M(38) );
R( b, c, d, e, a, F2, K2, M(39) );
R( a, b, c, d, e, F3, K3, M(40) );
R( e, a, b, c, d, F3, K3, M(41) );
R( d, e, a, b, c, F3, K3, M(42) );
R( c, d, e, a, b, F3, K3, M(43) );
R( b, c, d, e, a, F3, K3, M(44) );
R( a, b, c, d, e, F3, K3, M(45) );
R( e, a, b, c, d, F3, K3, M(46) );
R( d, e, a, b, c, F3, K3, M(47) );
R( c, d, e, a, b, F3, K3, M(48) );
R( b, c, d, e, a, F3, K3, M(49) );
R( a, b, c, d, e, F3, K3, M(50) );
R( e, a, b, c, d, F3, K3, M(51) );
R( d, e, a, b, c, F3, K3, M(52) );
R( c, d, e, a, b, F3, K3, M(53) );
R( b, c, d, e, a, F3, K3, M(54) );
R( a, b, c, d, e, F3, K3, M(55) );
R( e, a, b, c, d, F3, K3, M(56) );
R( d, e, a, b, c, F3, K3, M(57) );
R( c, d, e, a, b, F3, K3, M(58) );
R( b, c, d, e, a, F3, K3, M(59) );
R( a, b, c, d, e, F4, K4, M(60) );
R( e, a, b, c, d, F4, K4, M(61) );
R( d, e, a, b, c, F4, K4, M(62) );
R( c, d, e, a, b, F4, K4, M(63) );
R( b, c, d, e, a, F4, K4, M(64) );
R( a, b, c, d, e, F4, K4, M(65) );
R( e, a, b, c, d, F4, K4, M(66) );
R( d, e, a, b, c, F4, K4, M(67) );
R( c, d, e, a, b, F4, K4, M(68) );
R( b, c, d, e, a, F4, K4, M(69) );
R( a, b, c, d, e, F4, K4, M(70) );
R( e, a, b, c, d, F4, K4, M(71) );
R( d, e, a, b, c, F4, K4, M(72) );
R( c, d, e, a, b, F4, K4, M(73) );
R( b, c, d, e, a, F4, K4, M(74) );
R( a, b, c, d, e, F4, K4, M(75) );
R( e, a, b, c, d, F4, K4, M(76) );
R( d, e, a, b, c, F4, K4, M(77) );
R( c, d, e, a, b, F4, K4, M(78) );
R( b, c, d, e, a, F4, K4, M(79) );
a = ctx->A += a;
b = ctx->B += b;
c = ctx->C += c;
d = ctx->D += d;
e = ctx->E += e;
}
}