openssl:
I have been playing with the AES encryption code that I have "cut out"
of the sources and I recently tried using the AES_cbc_encrypt()
routine (defined in aes_cbc.c) - comparing it to some "know results" in
the WiMedia specifications. I found that the encryption operation was OK,
but the decryption operation gave the wrong result!! In either
case, (encryption/decryption) the routine is also doing something that
would appear to be wrong: it is overwriting the IV input string. I have
included "my" version of this file (that appears to work correctly in my
tests).
The details:
1. Testing done using VC++ v6.0 in Windows, but I believe this is not
relevant.
2. file: aes_cbc.c (same version in 0.9.8d and 0.9.8e)
-Bruce
/* crypto/aes/aes_cbc.c -*- mode:C; c-file-style: "eay" -*- */
/* ====================================================================
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*
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* modification, are permitted provided that the following conditions
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. All advertising materials mentioning features or use of this
* software must display the following acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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* endorse or promote products derived from this software without
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* [EMAIL PROTECTED]
*
* 5. Products derived from this software may not be called "OpenSSL"
* nor may "OpenSSL" appear in their names without prior written
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* 6. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit (http://www.openssl.org/)"
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* EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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*/
#ifndef AES_DEBUG
# ifndef NDEBUG
# define NDEBUG
# endif
#endif
#include <assert.h>
#include <openssl/aes.h>
#include "aes_locl.h"
/* --- do AES CBC encryption/decryption ---
06/19/07 BRK 1. fixed bug, it was writing back to IV
2. fixed bug, the decryption operation was wrong if in = out
*/
void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
const unsigned long length, const AES_KEY *key,
unsigned char *ivec, const int enc) {
unsigned long n;
unsigned long len = length;
unsigned char tmp[AES_BLOCK_SIZE];
unsigned char tmp1[AES_BLOCK_SIZE];
const unsigned char *iv = ivec;
assert(in && out && key && ivec);
assert((AES_ENCRYPT == enc)||(AES_DECRYPT == enc));
if (AES_ENCRYPT == enc)
{
while (len >= AES_BLOCK_SIZE)
{
for(n=0; n < AES_BLOCK_SIZE; ++n)
out[n] = in[n] ^ iv[n];
AES_encrypt(out, out, key);
iv = out;
len -= AES_BLOCK_SIZE;
in += AES_BLOCK_SIZE;
out += AES_BLOCK_SIZE;
}
if (len)
{
for(n=0; n < len; ++n)
out[n] = in[n] ^ iv[n];
for(n=len; n < AES_BLOCK_SIZE; ++n)
out[n] = iv[n];
AES_encrypt(out, out, key);
iv = out;
}
}
else /* do DECRYPT case */
if (in != out)
{
while (len >= AES_BLOCK_SIZE)
{
AES_decrypt(in, out, key);
for(n=0; n < AES_BLOCK_SIZE; ++n)
out[n] ^= iv[n];
iv = in;
len -= AES_BLOCK_SIZE;
in += AES_BLOCK_SIZE;
out += AES_BLOCK_SIZE;
}
if (len)
{
AES_decrypt(in,tmp,key);
for(n=0; n < len; ++n)
out[n] = tmp[n] ^ iv[n];
iv = in;
}
}
else
{
while (len >= AES_BLOCK_SIZE)
{
AES_decrypt(in, tmp1, key);
for(n=0; n < AES_BLOCK_SIZE; ++n)
tmp1[n] ^= iv[n];
memcpy(tmp, in, AES_BLOCK_SIZE);
memcpy(out, tmp1, AES_BLOCK_SIZE);
len -= AES_BLOCK_SIZE;
in += AES_BLOCK_SIZE;
out += AES_BLOCK_SIZE;
iv = tmp;
}
if (len)
{
AES_decrypt(in, tmp1, key);
for(n=0; n < len; ++n)
out[n] = tmp1[n] ^ iv[n];
for(n=len; n < AES_BLOCK_SIZE; ++n)
out[n] = iv[n];
}
}
} /* AES_cbc_encrypt */
