MD4 checksum fix

jw schultz jw at pegasys.ws
Sun Apr 6 10:47:16 EST 2003


On Sat, Apr 05, 2003 at 04:06:25PM -0800, cbarratt at users.sourceforge.net wrote:
> > > I agree, they should be done together.  I don't have my original
> > > patch but I can reimplement it with the correct remote_version
> > > dependence and send it in the next couple of days (by Thursday
> > > evening).  My intent is the minimal set of changes, rather than
> > > changing the internals.
> > 
> > That is a workable timeframe, thanks.
> 
> Two days late, but here is the patch against 2.5.6.  This implements the
> following changes:
> 
>  - for protocol version >= 27, mdfour_tail() is called when the block size
>    (including checksum_seed) is a multiple of 64.  Previously it was not
>    called, giving the wrong MD4 checksum.
> 
>  - for protocol version >= 27, a 64 bit bit counter is used in mdfour.c as
>    required by the RFC.  Previously only a 32 bit bit counter was used,
>    causing incorrect MD4 file checksums for file sizes >= 512MB - 4.
> 
> Craig

About the size (modulo comments) i was expecting.
I'll hold off committing until around the 9th to allow this
to be reviewed.

Glad i didn't miss your email.  Dirvish just got
a trial-by-fire test.

> 
> ###########################################################################
> diff -bur rsync-2.5.6/checksum.c rsync-2.5.6-fixed-md4/checksum.c
> --- rsync-2.5.6/checksum.c	2002-04-08 01:29:04.000000000 -0700
> +++ rsync-2.5.6-fixed-md4/checksum.c	2003-04-05 16:03:15.000000000 -0800
> @@ -74,7 +74,13 @@
>  	for(i = 0; i + CSUM_CHUNK <= len; i += CSUM_CHUNK) {
>  		mdfour_update(&m, (uchar *)(buf1+i), CSUM_CHUNK);
>  	}
> -	if (len - i > 0) {
> +	/*
> +	 * Prior to version 27 an incorrect MD4 checksum was computed
> +	 * by failing to call mdfour_tail() for block sizes that
> +	 * are multiples of 64.  This is fixed by calling mdfour_update()
> +	 * even when there are no more bytes.
> +	 */
> +	if (len - i > 0 || (remote_version >= 27 && len - i == 0)) {
>  		mdfour_update(&m, (uchar *)(buf1+i), (len-i));
>  	}
>  	
> @@ -105,8 +111,16 @@
>  		mdfour_update(&m, (uchar *)tmpchunk, CSUM_CHUNK);
>  	}
>  
> +	/*
> +	 * Prior to version 27 an incorrect MD4 checksum was computed
> +	 * by failing to call mdfour_tail() for block sizes that
> +	 * are multiples of 64.  This is fixed by calling mdfour_update()
> +	 * even when there are no more bytes.
> +	 */
> +	if (len - i > 0 || (remote_version >= 27 && len - i == 0)) {
>  	if (len - i > 0) {
>  		memcpy(tmpchunk, map_ptr(buf,i,len-i), len-i);
> +		}
>  		mdfour_update(&m, (uchar *)tmpchunk, (len-i));
>  	}
>  
> diff -bur rsync-2.5.6/lib/mdfour.c rsync-2.5.6-fixed-md4/lib/mdfour.c
> --- rsync-2.5.6/lib/mdfour.c	2001-06-27 22:07:15.000000000 -0700
> +++ rsync-2.5.6-fixed-md4/lib/mdfour.c	2003-04-05 16:04:46.000000000 -0800
> @@ -109,29 +109,53 @@
>  	md->C = 0x98badcfe;
>  	md->D = 0x10325476;
>  	md->totalN = 0;
> +	md->totalN2 = 0;
>  }
>  
>  
> -static void mdfour_tail(unsigned char *in, int n)
> +static void mdfour_tail(unsigned char *in, uint32 n)
>  {
>  	unsigned char buf[128];
>  	uint32 M[16];
> -	uint32 b;
> +	extern int remote_version;
>  
> -	m->totalN += n;
> -
> -	b = m->totalN * 8;
> +	/*
> +	 * Count total number of bits, modulo 2^64
> +	 */
> +	m->totalN += n << 3;
> +	if (m->totalN < (n << 3)) {
> +		m->totalN2++;
> +	}
> +	m->totalN2 += n >> 29;
>  
>  	memset(buf, 0, 128);
>  	if (n) memcpy(buf, in, n);
>  	buf[n] = 0x80;
>  
>  	if (n <= 55) {
> -		copy4(buf+56, b);
> +		copy4(buf+56, m->totalN);
> +		/*
> +		 * Prior to protocol version 27 only the number of bits
> +		 * modulo 2^32 was included.  MD4 requires the number
> +		 * of bits modulo 2^64, which was fixed starting with
> +		 * protocol version 27.
> +		 */
> +		if (remote_version >= 27) {
> +			copy4(buf+60, m->totalN2);
> +		}
>  		copy64(M, buf);
>  		mdfour64(M);
>  	} else {
> -		copy4(buf+120, b); 
> +		copy4(buf+120, m->totalN); 
> +		/*
> +		 * Prior to protocol version 27 only the number of bits
> +		 * modulo 2^32 was included.  MD4 requires the number
> +		 * of bits modulo 2^64, which was fixed starting with
> +		 * protocol version 27.
> +		 */
> +		if (remote_version >= 27) {
> +			copy4(buf+124, m->totalN2); 
> +		}
>  		copy64(M, buf);
>  		mdfour64(M);
>  		copy64(M, buf+64);
> @@ -139,20 +163,23 @@
>  	}
>  }
>  
> -void mdfour_update(struct mdfour *md, unsigned char *in, int n)
> +void mdfour_update(struct mdfour *md, unsigned char *in, uint32 n)
>  {
>  	uint32 M[16];
>  
> -	if (n == 0) mdfour_tail(in, n);
> -
>  	m = md;
>  
> +	if (n == 0) mdfour_tail(in, n);
> +
>  	while (n >= 64) {
>  		copy64(M, in);
>  		mdfour64(M);
>  		in += 64;
>  		n -= 64;
> -		m->totalN += 64;
> +		m->totalN += 64 << 3;
> +		if (m->totalN < 64 << 3) {
> +			m->totalN2++;
> +		}
>  	}
>  
>  	if (n) mdfour_tail(in, n);
> diff -bur rsync-2.5.6/lib/mdfour.h rsync-2.5.6-fixed-md4/lib/mdfour.h
> --- rsync-2.5.6/lib/mdfour.h	1998-10-28 21:01:52.000000000 -0800
> +++ rsync-2.5.6-fixed-md4/lib/mdfour.h	2003-04-04 14:25:50.000000000 -0800
> @@ -21,11 +21,12 @@
>  
>  struct mdfour {
>  	uint32 A, B, C, D;
> -	uint32 totalN;
> +	uint32 totalN;          /* bit count, lower 32 bits */
> +	uint32 totalN2;         /* bit count, upper 32 bits */
>  };
>  
>  void mdfour_begin(struct mdfour *md);
> -void mdfour_update(struct mdfour *md, unsigned char *in, int n);
> +void mdfour_update(struct mdfour *md, unsigned char *in, uint32 n);
>  void mdfour_result(struct mdfour *md, unsigned char *out);
>  void mdfour(unsigned char *out, unsigned char *in, int n);
>  
> -- 
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> 

-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt


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