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Fixed small padding error in the PKCS#1 PSS code.

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The existing LTC code for padding meassages for PSS signatures
contained a small error. In particular, the PSS-passing algorithms is
supposed to be given (bitlength of key - 1) as an argument. The LTC
code passes (bitlength of key), and subtracts 1 in the middle of the
PSS-padding. This subtraction unfortunately comes too late: a
calculation using that argument has already been made. Fortunately,
this bug only appeared if the bit-length of the key was 1 mod 8, and
so is unlikely to show up in practice. Still, this patch fixes the
problem.

Conflicts:
	src/pk/pkcs1/pkcs_1_pss_decode.c
This commit is contained in:
Jonathan Herzog 2008-01-20 22:45:58 -08:00 committed by Steffen Jaeckel
parent fe1b6eced7
commit 3324da2601
3 changed files with 15 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
src/pk/pkcs1/pkcs_1_pss_decode.c
View File

@ -51,11 +51,12 @@ int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen,
} }
hLen = hash_descriptor[hash_idx].hashsize; hLen = hash_descriptor[hash_idx].hashsize;
modulus_bitlen--;
modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
/* check sizes */ /* check sizes */
if ((saltlen > modulus_len) || if ((saltlen > modulus_len) ||
(modulus_len < hLen + saltlen + 2) || (siglen != modulus_len)) { (modulus_len < hLen + saltlen + 2)) {
return CRYPT_PK_INVALID_SIZE; return CRYPT_PK_INVALID_SIZE;
} }
@ -95,8 +96,9 @@ int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen,
XMEMCPY(hash, sig + x, hLen); XMEMCPY(hash, sig + x, hLen);
x += hLen; x += hLen;
/* check the MSB */ /* check the MSB */
if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)))) != 0) { if ((sig[0] & ~(0xFF >> ((modulus_len<<3) - (modulus_bitlen)))) != 0) {
err = CRYPT_INVALID_PACKET; err = CRYPT_INVALID_PACKET;
goto LBL_ERR; goto LBL_ERR;
} }
@ -112,7 +114,7 @@ int pkcs_1_pss_decode(const unsigned char *msghash, unsigned long msghashlen,
} }
/* now clear the first byte [make sure smaller than modulus] */ /* now clear the first byte [make sure smaller than modulus] */
DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)); DB[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen));
/* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */ /* DB = PS || 0x01 || salt, PS == modulus_len - saltlen - hLen - 2 zero bytes */

3
src/pk/pkcs1/pkcs_1_pss_encode.c
View File

@ -54,6 +54,7 @@ int pkcs_1_pss_encode(const unsigned char *msghash, unsigned long msghashlen,
} }
hLen = hash_descriptor[hash_idx].hashsize; hLen = hash_descriptor[hash_idx].hashsize;
modulus_bitlen--;
modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); modulus_len = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
/* check sizes */ /* check sizes */
@ -147,7 +148,7 @@ int pkcs_1_pss_encode(const unsigned char *msghash, unsigned long msghashlen,
out[y] = 0xBC; out[y] = 0xBC;
/* now clear the 8*modulus_len - modulus_bitlen most significant bits */ /* now clear the 8*modulus_len - modulus_bitlen most significant bits */
out[0] &= 0xFF >> ((modulus_len<<3) - (modulus_bitlen-1)); out[0] &= 0xFF >> ((modulus_len<<3) - modulus_bitlen);
/* store output size */ /* store output size */
*outlen = modulus_len; *outlen = modulus_len;

9
src/pk/rsa/rsa_verify_hash.c
View File

@ -92,7 +92,14 @@ int rsa_verify_hash_ex(const unsigned char *sig, unsigned long siglen,
if (padding == LTC_PKCS_1_PSS) { if (padding == LTC_PKCS_1_PSS) {
/* PSS decode and verify it */ /* PSS decode and verify it */
err = pkcs_1_pss_decode(hash, hashlen, tmpbuf, x, saltlen, hash_idx, modulus_bitlen, stat);
if(modulus_bitlen%8 == 1){
err = pkcs_1_pss_decode(hash, hashlen, tmpbuf+1, x-1, saltlen, hash_idx, modulus_bitlen, stat);
}
else{
err = pkcs_1_pss_decode(hash, hashlen, tmpbuf, x, saltlen, hash_idx, modulus_bitlen, stat);
}
} else { } else {
/* PKCS #1 v1.5 decode it */ /* PKCS #1 v1.5 decode it */
unsigned char *out; unsigned char *out;