mirror of
https://github.com/trezor/trezor-firmware.git
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127 lines
4.0 KiB
C
127 lines
4.0 KiB
C
/*
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* Copyright 2013 The Android Open Source Project
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of Google Inc. nor the names of its contributors may
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* be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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* EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <string.h>
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#include "dsa_sig.h"
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#include "p256.h"
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/**
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* Trims off the leading zero bytes and copy it to a buffer aligning it to the end.
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*/
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static inline int trim_to_p256_bytes(unsigned char dst[P256_NBYTES], unsigned char *src,
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int src_len) {
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int dst_offset;
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while (*src == '\0' && src_len > 0) {
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src++;
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src_len--;
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}
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if (src_len > P256_NBYTES || src_len < 1) {
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return 0;
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}
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dst_offset = P256_NBYTES - src_len;
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memset(dst, 0, dst_offset);
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memcpy(dst + dst_offset, src, src_len);
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return 1;
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}
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/**
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* Unpacks the ASN.1 DSA signature sequence.
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*/
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int dsa_sig_unpack(unsigned char* sig, int sig_len, p256_int* r_int, p256_int* s_int) {
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/*
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* Structure is:
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* 0x30 0xNN SEQUENCE + s_length
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* 0x02 0xNN INTEGER + r_length
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* 0xAA 0xBB .. r_length bytes of "r" (offset 4)
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* 0x02 0xNN INTEGER + s_length
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* 0xMM 0xNN .. s_length bytes of "s" (offset 6 + r_len)
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*/
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int seq_len;
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unsigned char r_bytes[P256_NBYTES];
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unsigned char s_bytes[P256_NBYTES];
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int r_len;
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int s_len;
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memset(r_bytes, 0, sizeof(r_bytes));
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memset(s_bytes, 0, sizeof(s_bytes));
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/*
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* Must have at least:
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* 2 bytes sequence header and length
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* 2 bytes R integer header and length
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* 1 byte of R
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* 2 bytes S integer header and length
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* 1 byte of S
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*
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* 8 bytes total
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*/
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if (sig_len < 8 || sig[0] != 0x30 || sig[2] != 0x02) {
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return 0;
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}
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seq_len = sig[1];
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if ((seq_len <= 0) || (seq_len + 2 != sig_len)) {
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return 0;
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}
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r_len = sig[3];
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/*
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* Must have at least:
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* 2 bytes for R header and length
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* 2 bytes S integer header and length
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* 1 byte of S
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*/
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if ((r_len < 1) || (r_len > seq_len - 5) || (sig[4 + r_len] != 0x02)) {
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return 0;
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}
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s_len = sig[5 + r_len];
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/**
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* Must have:
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* 2 bytes for R header and length
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* r_len bytes for R
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* 2 bytes S integer header and length
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*/
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if ((s_len < 1) || (s_len != seq_len - 4 - r_len)) {
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return 0;
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}
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/*
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* ASN.1 encoded integers are zero-padded for positive integers. Make sure we have
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* a correctly-sized buffer and that the resulting integer isn't too large.
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*/
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if (!trim_to_p256_bytes(r_bytes, &sig[4], r_len)
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|| !trim_to_p256_bytes(s_bytes, &sig[6 + r_len], s_len)) {
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return 0;
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}
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p256_from_bin(r_bytes, r_int);
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p256_from_bin(s_bytes, s_int);
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return 1;
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}
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