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/*
* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/* see bearssl_ec.h */
size_t
br_ecdsa_asn1_to_raw(void *sig, size_t sig_len)
{
/*
* Note: this code is a bit lenient in that it accepts a few
* deviations to DER with regards to minimality of encoding of
* lengths and integer values. These deviations are still
* unambiguous.
*
* Signature format is a SEQUENCE of two INTEGER values. We
* support only integers of less than 127 bytes each (signed
* encoding) so the resulting raw signature will have length
* at most 254 bytes.
*/
unsigned char *buf, *r, *s;
size_t zlen, rlen, slen, off;
unsigned char tmp[254];
buf = sig;
if (sig_len < 8) {
return 0;
}
/*
* First byte is SEQUENCE tag.
*/
if (buf[0] != 0x30) {
return 0;
}
/*
* The SEQUENCE length will be encoded over one or two bytes. We
* limit the total SEQUENCE contents to 255 bytes, because it
* makes things simpler; this is enough for subgroup orders up
* to 999 bits.
*/
zlen = buf[1];
if (zlen > 0x80) {
if (zlen != 0x81) {
return 0;
}
zlen = buf[2];
if (zlen != sig_len - 3) {
return 0;
}
off = 3;
} else {
if (zlen != sig_len - 2) {
return 0;
}
off = 2;
}
/*
* First INTEGER (r).
*/
if (buf[off ++] != 0x02) {
return 0;
}
rlen = buf[off ++];
if (rlen >= 0x80) {
return 0;
}
r = buf + off;
off += rlen;
/*
* Second INTEGER (s).
*/
if (off + 2 > sig_len) {
return 0;
}
if (buf[off ++] != 0x02) {
return 0;
}
slen = buf[off ++];
if (slen >= 0x80 || slen != sig_len - off) {
return 0;
}
s = buf + off;
/*
* Removing leading zeros from r and s.
*/
while (rlen > 0 && *r == 0) {
rlen --;
r ++;
}
while (slen > 0 && *s == 0) {
slen --;
s ++;
}
/*
* Compute common length for the two integers, then copy integers
* into the temporary buffer, and finally copy it back over the
* signature buffer.
*/
zlen = rlen > slen ? rlen : slen;
sig_len = zlen << 1;
memset(tmp, 0, sig_len);
memcpy(tmp + zlen - rlen, r, rlen);
memcpy(tmp + sig_len - slen, s, slen);
memcpy(sig, tmp, sig_len);
return sig_len;
}
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