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/*
* Copyright (c) 2018 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"
/*
* Hash some data. This is put as a separate function so that stack
* allocation of the hash function context is done only for the duration
* of the hash.
*/
static void
hash_data(const br_hash_class *dig, void *dst, const void *src, size_t len)
{
br_hash_compat_context hc;
hc.vtable = dig;
dig->init(&hc.vtable);
dig->update(&hc.vtable, src, len);
dig->out(&hc.vtable, dst);
}
/* see inner.h */
size_t
br_rsa_oaep_pad(const br_prng_class **rnd, const br_hash_class *dig,
const void *label, size_t label_len,
const br_rsa_public_key *pk,
void *dst, size_t dst_max_len,
const void *src, size_t src_len)
{
size_t k, hlen;
unsigned char *buf;
hlen = br_digest_size(dig);
/*
* Compute actual modulus length (in bytes).
*/
k = pk->nlen;
while (k > 0 && pk->n[k - 1] == 0) {
k --;
}
/*
* An error is reported if:
* - the modulus is too short;
* - the source message length is too long;
* - the destination buffer is too short.
*/
if (k < ((hlen << 1) + 2)
|| src_len > (k - (hlen << 1) - 2)
|| dst_max_len < k)
{
return 0;
}
/*
* Apply padding. At this point, things cannot fail.
*/
buf = dst;
/*
* Assemble: DB = lHash || PS || 0x01 || M
* We first place the source message M with memmove(), so that
* overlaps between source and destination buffers are supported.
*/
memmove(buf + k - src_len, src, src_len);
hash_data(dig, buf + 1 + hlen, label, label_len);
memset(buf + 1 + (hlen << 1), 0, k - src_len - (hlen << 1) - 2);
buf[k - src_len - 1] = 0x01;
/*
* Make the random seed.
*/
(*rnd)->generate(rnd, buf + 1, hlen);
/*
* Mask DB with the mask generated from the seed.
*/
br_mgf1_xor(buf + 1 + hlen, k - hlen - 1, dig, buf + 1, hlen);
/*
* Mask the seed with the mask generated from the masked DB.
*/
br_mgf1_xor(buf + 1, hlen, dig, buf + 1 + hlen, k - hlen - 1);
/*
* Padding result: EM = 0x00 || maskedSeed || maskedDB.
*/
buf[0] = 0x00;
return k;
}
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