/*
* Copyright (c) 2016 Thomas Pornin
*
* 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_rsa.h */
uint32_t
br_rsa_i31_pkcs1_sign(const unsigned char *hash_oid,
const unsigned char *hash, size_t hash_len,
const br_rsa_private_key *sk, unsigned char *x)
{
size_t u, x3, xlen;
/*
* Padded hash value has format:
* 00 01 FF .. FF 00 30 x1 30 x2 06 x3 OID 05 00 04 x4 HASH
*
* with the following rules:
*
* -- Total length is equal to the modulus length (unsigned
* encoding).
*
* -- There must be at least eight bytes of value 0xFF.
*
* -- x4 is equal to the hash length (hash_len).
*
* -- x3 is equal to the encoded OID value length (hash_oid[0]).
*
* -- x2 = x3 + 4.
*
* -- x1 = x2 + x4 + 4 = x3 + x4 + 8.
*
* Note: the "05 00" is optional (signatures with and without
* that sequence exist in practice), but notes in PKCS#1 seem to
* indicate that the presence of that sequence (specifically,
* an ASN.1 NULL value for the hash parameters) may be slightly
* more "standard" than the opposite.
*/
xlen = (sk->n_bitlen + 7) >> 3;
if (hash_oid == NULL) {
if (xlen < hash_len + 11) {
return 0;
}
x[0] = 0x00;
x[1] = 0x01;
u = xlen - hash_len;
memset(x + 2, 0xFF, u - 3);
x[u - 1] = 0x00;
} else {
x3 = hash_oid[0];
/*
* Check that there is enough room for all the elements,
* including at least eight bytes of value 0xFF.
*/
if (xlen < (x3 + hash_len + 21)) {
return 0;
}
x[0] = 0x00;
x[1] = 0x01;
u = xlen - x3 - hash_len - 11;
memset(x + 2, 0xFF, u - 2);
x[u] = 0x00;
x[u + 1] = 0x30;
x[u + 2] = x3 + hash_len + 8;
x[u + 3] = 0x30;
x[u + 4] = x3 + 4;
x[u + 5] = 0x06;
memcpy(x + u + 6, hash_oid, x3 + 1);
u += x3 + 7;
x[u ++] = 0x05;
x[u ++] = 0x00;
x[u ++] = 0x04;
x[u ++] = hash_len;
}
memcpy(x + u, hash, hash_len);
/*
* Do the actual computation.
*/
return br_rsa_i31_private(x, sk);
}