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/*
* Copyright 2013 The Android Open Source Project
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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.
* * Neither the name of Google Inc. nor the names of its contributors may
* be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS 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 Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <string.h>
#include "mincrypt/dsa_sig.h"
#include "mincrypt/p256.h"
/**
* Trims off the leading zero bytes and copy it to a buffer aligning it to the end.
*/
static inline int trim_to_p256_bytes(unsigned char dst[P256_NBYTES], unsigned char *src,
int src_len) {
int dst_offset;
while (*src == '\0' && src_len > 0) {
src++;
src_len--;
}
if (src_len > P256_NBYTES || src_len < 1) {
return 0;
}
dst_offset = P256_NBYTES - src_len;
memset(dst, 0, dst_offset);
memcpy(dst + dst_offset, src, src_len);
return 1;
}
/**
* Unpacks the ASN.1 DSA signature sequence.
*/
int dsa_sig_unpack(unsigned char* sig, int sig_len, p256_int* r_int, p256_int* s_int) {
/*
* Structure is:
* 0x30 0xNN SEQUENCE + s_length
* 0x02 0xNN INTEGER + r_length
* 0xAA 0xBB .. r_length bytes of "r" (offset 4)
* 0x02 0xNN INTEGER + s_length
* 0xMM 0xNN .. s_length bytes of "s" (offset 6 + r_len)
*/
int seq_len;
unsigned char r_bytes[P256_NBYTES];
unsigned char s_bytes[P256_NBYTES];
int r_len;
int s_len;
memset(r_bytes, 0, sizeof(r_bytes));
memset(s_bytes, 0, sizeof(s_bytes));
/*
* Must have at least:
* 2 bytes sequence header and length
* 2 bytes R integer header and length
* 1 byte of R
* 2 bytes S integer header and length
* 1 byte of S
*
* 8 bytes total
*/
if (sig_len < 8 || sig[0] != 0x30 || sig[2] != 0x02) {
return 0;
}
seq_len = sig[1];
if ((seq_len <= 0) || (seq_len + 2 != sig_len)) {
return 0;
}
r_len = sig[3];
/*
* Must have at least:
* 2 bytes for R header and length
* 2 bytes S integer header and length
* 1 byte of S
*/
if ((r_len < 1) || (r_len > seq_len - 5) || (sig[4 + r_len] != 0x02)) {
return 0;
}
s_len = sig[5 + r_len];
/**
* Must have:
* 2 bytes for R header and length
* r_len bytes for R
* 2 bytes S integer header and length
*/
if ((s_len < 1) || (s_len != seq_len - 4 - r_len)) {
return 0;
}
/*
* ASN.1 encoded integers are zero-padded for positive integers. Make sure we have
* a correctly-sized buffer and that the resulting integer isn't too large.
*/
if (!trim_to_p256_bytes(r_bytes, &sig[4], r_len)
|| !trim_to_p256_bytes(s_bytes, &sig[6 + r_len], s_len)) {
return 0;
}
p256_from_bin(r_bytes, r_int);
p256_from_bin(s_bytes, s_int);
return 1;
}
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