/*
* Copyright (c) 2017 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"
/*
* Implementation Notes
* ====================
*
* Since CTR and GHASH implementations can handle only full blocks, a
* 16-byte buffer (buf[]) is maintained in the context:
*
* - When processing AAD, buf[] contains the 0-15 unprocessed bytes.
*
* - When doing CTR encryption / decryption, buf[] contains the AES output
* for the last partial block, to be used with the next few bytes of
* data, as well as the already encrypted bytes. For instance, if the
* processed data length so far is 21 bytes, then buf[0..4] contains
* the five last encrypted bytes, and buf[5..15] contains the next 11
* AES output bytes to be XORed with the next 11 bytes of input.
*
* The recorded AES output bytes are used to complete the block when
* the corresponding bytes are obtained. Note that buf[] always
* contains the _encrypted_ bytes, whether we apply encryption or
* decryption: these bytes are used as input to GHASH when the block
* is complete.
*
* In both cases, the low bits of the data length counters (count_aad,
* count_ctr) are used to work out the current situation.
*/
/* see bearssl_aead.h */
void
br_gcm_init(br_gcm_context *ctx, const br_block_ctr_class **bctx, br_ghash gh)
{
unsigned char iv[12];
ctx->vtable = &br_gcm_vtable;
ctx->bctx = bctx;
ctx->gh = gh;
/*
* The GHASH key h[] is the raw encryption of the all-zero
* block. Since we only have a CTR implementation, we use it
* with an all-zero IV and a zero counter, to CTR-encrypt an
* all-zero block.
*/
memset(ctx->h, 0, sizeof ctx->h);
memset(iv, 0, sizeof iv);
(*bctx)->run(bctx, iv, 0, ctx->h, sizeof ctx->h);
}
/* see bearssl_aead.h */
void
br_gcm_reset(br_gcm_context *ctx, const void *iv, size_t len)
{
/*
* If the provided nonce is 12 bytes, then this is the initial
* IV for CTR mode; it will be used with a counter that starts
* at 2 (value 1 is for encrypting the GHASH output into the tag).
*
* If the provided nonce has any other length, then it is hashed
* (with GHASH) into a 16-byte value that will be the IV for CTR
* (both 12-byte IV and 32-bit counter).
*/
if (len == 12) {
memcpy(ctx->j0_1, iv, 12);
ctx->j0_2 = 1;
} else {
unsigned char ty[16], tmp[16];
memset(ty, 0, sizeof ty);
ctx->gh(ty, ctx->h, iv, len);
memset(tmp, 0, 8);
br_enc64be(tmp + 8, (uint64_t)len << 3);
ctx->gh(ty, ctx->h, tmp, 16);
memcpy(ctx->j0_1, ty, 12);
ctx->j0_2 = br_dec32be(ty + 12);
}
ctx->jc = ctx->j0_2 + 1;
memset(ctx->y, 0, sizeof ctx->y);
ctx->count_aad = 0;
ctx->count_ctr = 0;
}
/* see bearssl_aead.h */
void
br_gcm_aad_inject(br_gcm_context *ctx, const void *data, size_t len)
{
size_t ptr, dlen;
ptr = (size_t)ctx->count_aad & (size_t)15;
if (ptr != 0) {
/*
* If there is a partial block, then we first try to
* complete it.
*/
size_t clen;
clen = 16 - ptr;
if (len < clen) {
memcpy(ctx->buf + ptr, data, len);
ctx->count_aad += (uint64_t)len;
return;
}
memcpy(ctx->buf + ptr, data, clen);
ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
data = (const unsigned char *)data + clen;
len -= clen;
ctx->count_aad += (uint64_t)clen;
}
/*
* Now AAD is aligned on a 16-byte block (with regards to GHASH).
* We process all complete blocks, and save the last partial
* block.
*/
dlen = len & ~(size_t)15;
ctx->gh(ctx->y, ctx->h, data, dlen);
memcpy(ctx->buf, (const unsigned char *)data + dlen, len - dlen);
ctx->count_aad += (uint64_t)len;
}
/* see bearssl_aead.h */
void
br_gcm_flip(br_gcm_context *ctx)
{
/*
* We complete the GHASH computation if there is a partial block.
* The GHASH implementation automatically applies padding with
* zeros.
*/
size_t ptr;
ptr = (size_t)ctx->count_aad & (size_t)15;
if (ptr != 0) {
ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
}
}
/* see bearssl_aead.h */
void
br_gcm_run(br_gcm_context *ctx, int encrypt, void *data, size_t len)
{
unsigned char *buf;
size_t ptr, dlen;
buf = data;
ptr = (size_t)ctx->count_ctr & (size_t)15;
if (ptr != 0) {
/*
* If we have a partial block, then we try to complete it.
*/
size_t u, clen;
clen = 16 - ptr;
if (len < clen) {
clen = len;
}
for (u = 0; u < clen; u ++) {
unsigned x, y;
x = buf[u];
y = x ^ ctx->buf[ptr + u];
ctx->buf[ptr + u] = encrypt ? y : x;
buf[u] = y;
}
ctx->count_ctr += (uint64_t)clen;
buf += clen;
len -= clen;
if (ptr + clen < 16) {
return;
}
ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
}
/*
* Process full blocks.
*/
dlen = len & ~(size_t)15;
if (!encrypt) {
ctx->gh(ctx->y, ctx->h, buf, dlen);
}
ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->jc, buf, dlen);
if (encrypt) {
ctx->gh(ctx->y, ctx->h, buf, dlen);
}
buf += dlen;
len -= dlen;
ctx->count_ctr += (uint64_t)dlen;
if (len > 0) {
/*
* There is a partial block.
*/
size_t u;
memset(ctx->buf, 0, sizeof ctx->buf);
ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1,
ctx->jc, ctx->buf, 16);
for (u = 0; u < len; u ++) {
unsigned x, y;
x = buf[u];
y = x ^ ctx->buf[u];
ctx->buf[u] = encrypt ? y : x;
buf[u] = y;
}
ctx->count_ctr += (uint64_t)len;
}
}
/* see bearssl_aead.h */
void
br_gcm_get_tag(br_gcm_context *ctx, void *tag)
{
size_t ptr;
unsigned char tmp[16];
ptr = (size_t)ctx->count_ctr & (size_t)15;
if (ptr > 0) {
/*
* There is a partial block: encrypted/decrypted data has
* been produced, but the encrypted bytes must still be
* processed by GHASH.
*/
ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
}
/*
* Final block for GHASH: the AAD and plaintext lengths (in bits).
*/
br_enc64be(tmp, ctx->count_aad << 3);
br_enc64be(tmp + 8, ctx->count_ctr << 3);
ctx->gh(ctx->y, ctx->h, tmp, 16);
/*
* Tag is the GHASH output XORed with the encryption of the
* nonce with the initial counter value.
*/
memcpy(tag, ctx->y, 16);
(*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->j0_2, tag, 16);
}
/* see bearssl_aead.h */
void
br_gcm_get_tag_trunc(br_gcm_context *ctx, void *tag, size_t len)
{
unsigned char tmp[16];
br_gcm_get_tag(ctx, tmp);
memcpy(tag, tmp, len);
}
/* see bearssl_aead.h */
uint32_t
br_gcm_check_tag_trunc(br_gcm_context *ctx, const void *tag, size_t len)
{
unsigned char tmp[16];
size_t u;
int x;
br_gcm_get_tag(ctx, tmp);
x = 0;
for (u = 0; u < len; u ++) {
x |= tmp[u] ^ ((const unsigned char *)tag)[u];
}
return EQ0(x);
}
/* see bearssl_aead.h */
uint32_t
br_gcm_check_tag(br_gcm_context *ctx, const void *tag)
{
return br_gcm_check_tag_trunc(ctx, tag, 16);
}
/* see bearssl_aead.h */
const br_aead_class br_gcm_vtable = {
16,
(void (*)(const br_aead_class **, const void *, size_t))
&br_gcm_reset,
(void (*)(const br_aead_class **, const void *, size_t))
&br_gcm_aad_inject,
(void (*)(const br_aead_class **))
&br_gcm_flip,
(void (*)(const br_aead_class **, int, void *, size_t))
&br_gcm_run,
(void (*)(const br_aead_class **, void *))
&br_gcm_get_tag,
(uint32_t (*)(const br_aead_class **, const void *))
&br_gcm_check_tag,
(void (*)(const br_aead_class **, void *, size_t))
&br_gcm_get_tag_trunc,
(uint32_t (*)(const br_aead_class **, const void *, size_t))
&br_gcm_check_tag_trunc
};