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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"
/*
* GCM initialisation. This does everything except setting the vtable,
* which depends on whether this is a context for encrypting or for
* decrypting.
*/
static void
gen_gcm_init(br_sslrec_gcm_context *cc,
const br_block_ctr_class *bc_impl,
const void *key, size_t key_len,
br_ghash gh_impl,
const void *iv)
{
unsigned char tmp[12];
cc->seq = 0;
bc_impl->init(&cc->bc.vtable, key, key_len);
cc->gh = gh_impl;
memcpy(cc->iv, iv, sizeof cc->iv);
memset(cc->h, 0, sizeof cc->h);
memset(tmp, 0, sizeof tmp);
bc_impl->run(&cc->bc.vtable, tmp, 0, cc->h, sizeof cc->h);
}
static void
in_gcm_init(br_sslrec_gcm_context *cc,
const br_block_ctr_class *bc_impl,
const void *key, size_t key_len,
br_ghash gh_impl,
const void *iv)
{
cc->vtable.in = &br_sslrec_in_gcm_vtable;
gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
}
static int
gcm_check_length(const br_sslrec_gcm_context *cc, size_t rlen)
{
/*
* GCM adds a fixed overhead:
* 8 bytes for the nonce_explicit (before the ciphertext)
* 16 bytes for the authentication tag (after the ciphertext)
*/
(void)cc;
return rlen >= 24 && rlen <= (16384 + 24);
}
/*
* Compute the authentication tag. The value written in 'tag' must still
* be CTR-encrypted.
*/
static void
do_tag(br_sslrec_gcm_context *cc,
int record_type, unsigned version,
void *data, size_t len, void *tag)
{
unsigned char header[13];
unsigned char footer[16];
/*
* Compute authentication tag. Three elements must be injected in
* sequence, each possibly 0-padded to reach a length multiple
* of the block size: the 13-byte header (sequence number, record
* type, protocol version, record length), the cipher text, and
* the word containing the encodings of the bit lengths of the two
* other elements.
*/
br_enc64be(header, cc->seq ++);
header[8] = (unsigned char)record_type;
br_enc16be(header + 9, version);
br_enc16be(header + 11, len);
br_enc64be(footer, (uint64_t)(sizeof header) << 3);
br_enc64be(footer + 8, (uint64_t)len << 3);
memset(tag, 0, 16);
cc->gh(tag, cc->h, header, sizeof header);
cc->gh(tag, cc->h, data, len);
cc->gh(tag, cc->h, footer, sizeof footer);
}
/*
* Do CTR encryption. This also does CTR encryption of a single block at
* address 'xortag' with the counter value appropriate for the final
* processing of the authentication tag.
*/
static void
do_ctr(br_sslrec_gcm_context *cc, const void *nonce, void *data, size_t len,
void *xortag)
{
unsigned char iv[12];
memcpy(iv, cc->iv, 4);
memcpy(iv + 4, nonce, 8);
cc->bc.vtable->run(&cc->bc.vtable, iv, 2, data, len);
cc->bc.vtable->run(&cc->bc.vtable, iv, 1, xortag, 16);
}
static unsigned char *
gcm_decrypt(br_sslrec_gcm_context *cc,
int record_type, unsigned version, void *data, size_t *data_len)
{
unsigned char *buf;
size_t len, u;
uint32_t bad;
unsigned char tag[16];
buf = (unsigned char *)data + 8;
len = *data_len - 24;
do_tag(cc, record_type, version, buf, len, tag);
do_ctr(cc, data, buf, len, tag);
/*
* Compare the computed tag with the value from the record. It
* is possibly useless to do a constant-time comparison here,
* but it does not hurt.
*/
bad = 0;
for (u = 0; u < 16; u ++) {
bad |= tag[u] ^ buf[len + u];
}
if (bad) {
return NULL;
}
*data_len = len;
return buf;
}
/* see bearssl_ssl.h */
const br_sslrec_in_gcm_class br_sslrec_in_gcm_vtable = {
{
sizeof(br_sslrec_gcm_context),
(int (*)(const br_sslrec_in_class *const *, size_t))
&gcm_check_length,
(unsigned char *(*)(const br_sslrec_in_class **,
int, unsigned, void *, size_t *))
&gcm_decrypt
},
(void (*)(const br_sslrec_in_gcm_class **,
const br_block_ctr_class *, const void *, size_t,
br_ghash, const void *))
&in_gcm_init
};
static void
out_gcm_init(br_sslrec_gcm_context *cc,
const br_block_ctr_class *bc_impl,
const void *key, size_t key_len,
br_ghash gh_impl,
const void *iv)
{
cc->vtable.out = &br_sslrec_out_gcm_vtable;
gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
}
static void
gcm_max_plaintext(const br_sslrec_gcm_context *cc,
size_t *start, size_t *end)
{
size_t len;
(void)cc;
*start += 8;
len = *end - *start - 16;
if (len > 16384) {
len = 16384;
}
*end = *start + len;
}
static unsigned char *
gcm_encrypt(br_sslrec_gcm_context *cc,
int record_type, unsigned version, void *data, size_t *data_len)
{
unsigned char *buf;
size_t u, len;
unsigned char tmp[16];
buf = (unsigned char *)data;
len = *data_len;
memset(tmp, 0, sizeof tmp);
br_enc64be(buf - 8, cc->seq);
do_ctr(cc, buf - 8, buf, len, tmp);
do_tag(cc, record_type, version, buf, len, buf + len);
for (u = 0; u < 16; u ++) {
buf[len + u] ^= tmp[u];
}
len += 24;
buf -= 13;
buf[0] = (unsigned char)record_type;
br_enc16be(buf + 1, version);
br_enc16be(buf + 3, len);
*data_len = len + 5;
return buf;
}
/* see bearssl_ssl.h */
const br_sslrec_out_gcm_class br_sslrec_out_gcm_vtable = {
{
sizeof(br_sslrec_gcm_context),
(void (*)(const br_sslrec_out_class *const *,
size_t *, size_t *))
&gcm_max_plaintext,
(unsigned char *(*)(const br_sslrec_out_class **,
int, unsigned, void *, size_t *))
&gcm_encrypt
},
(void (*)(const br_sslrec_out_gcm_class **,
const br_block_ctr_class *, const void *, size_t,
br_ghash, const void *))
&out_gcm_init
};
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