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Diffstat (limited to 'libmincrypt/dsa_sig.c')
| -rw-r--r-- | libmincrypt/dsa_sig.c | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/libmincrypt/dsa_sig.c b/libmincrypt/dsa_sig.c new file mode 100644 index 000000000..101314bd9 --- /dev/null +++ b/libmincrypt/dsa_sig.c @@ -0,0 +1,126 @@ +/* + * 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; +} |