Added general-purpose API for AEAD algorithms, and GCM implementation.
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Thomas Pornin
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4aac1cd5c6
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127fb4a31d
6 changed files with 1024 additions and 4 deletions
296
src/aead/gcm.c
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296
src/aead/gcm.c
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/*
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* Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "inner.h"
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/*
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* Implementation Notes
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* ====================
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*
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* Since CTR and GHASH implementations can handle only full blocks, a
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* 16-byte buffer (buf[]) is maintained in the context:
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*
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* - When processing AAD, buf[] contains the 0-15 unprocessed bytes.
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*
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* - When doing CTR encryption / decryption, buf[] contains the AES output
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* for the last partial block, to be used with the next few bytes of
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* data, as well as the already encrypted bytes. For instance, if the
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* processed data length so far is 21 bytes, then buf[0..4] contains
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* the five last encrypted bytes, and buf[5..15] contains the next 11
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* AES output bytes to be XORed with the next 11 bytes of input.
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*
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* The recorded AES output bytes are used to complete the block when
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* the corresponding bytes are obtained. Note that buf[] always
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* contains the _encrypted_ bytes, whether we apply encryption or
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* decryption: these bytes are used as input to GHASH when the block
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* is complete.
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*
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* In both cases, the low bits of the data length counters (count_aad,
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* count_ctr) are used to work out the current situation.
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*/
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/* see bearssl_aead.h */
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void
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br_gcm_init(br_gcm_context *ctx, const br_block_ctr_class **bctx, br_ghash gh)
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{
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unsigned char iv[12];
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ctx->bctx = bctx;
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ctx->gh = gh;
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/*
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* The GHASH key h[] is the raw encryption of the all-zero
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* block. Since we only have a CTR implementation, we use it
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* with an all-zero IV and a zero counter, to CTR-encrypt an
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* all-zero block.
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*/
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memset(ctx->h, 0, sizeof ctx->h);
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memset(iv, 0, sizeof iv);
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(*bctx)->run(bctx, iv, 0, ctx->h, sizeof ctx->h);
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}
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/* see bearssl_aead.h */
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void
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br_gcm_reset(br_gcm_context *ctx, const void *iv, size_t len)
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{
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/*
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* If the provided nonce is 12 bytes, then this is the initial
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* IV for CTR mode; it will be used with a counter that starts
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* at 2 (value 1 is for encrypting the GHASH output into the tag).
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*
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* If the provided nonce has any other length, then it is hashed
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* (with GHASH) into a 16-byte value that will be the IV for CTR
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* (both 12-byte IV and 32-bit counter).
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*/
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if (len == 12) {
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memcpy(ctx->j0_1, iv, 12);
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ctx->j0_2 = 1;
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} else {
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unsigned char ty[16], tmp[16];
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memset(ty, 0, sizeof ty);
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ctx->gh(ty, ctx->h, iv, len);
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memset(tmp, 0, 8);
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br_enc64be(tmp + 8, (uint64_t)len << 3);
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ctx->gh(ty, ctx->h, tmp, 16);
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memcpy(ctx->j0_1, ty, 12);
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ctx->j0_2 = br_dec32be(ty + 12);
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}
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ctx->jc = ctx->j0_2 + 1;
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memset(ctx->y, 0, sizeof ctx->y);
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ctx->count_aad = 0;
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ctx->count_ctr = 0;
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}
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/* see bearssl_aead.h */
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void
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br_gcm_aad_inject(br_gcm_context *ctx, const void *data, size_t len)
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{
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size_t ptr, dlen;
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ptr = (size_t)ctx->count_aad & (size_t)15;
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if (ptr != 0) {
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/*
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* If there is a partial block, then we first try to
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* complete it.
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*/
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size_t clen;
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clen = 16 - ptr;
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if (len < clen) {
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memcpy(ctx->buf + ptr, data, len);
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ctx->count_aad += (uint64_t)len;
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return;
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}
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memcpy(ctx->buf + ptr, data, clen);
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ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
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data = (const unsigned char *)data + clen;
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len -= clen;
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ctx->count_aad += (uint64_t)clen;
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}
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/*
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* Now AAD is aligned on a 16-byte block (with regards to GHASH).
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* We process all complete blocks, and save the last partial
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* block.
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*/
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dlen = len & ~(size_t)15;
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ctx->gh(ctx->y, ctx->h, data, dlen);
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memcpy(ctx->buf, (const unsigned char *)data + dlen, len - dlen);
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ctx->count_aad += (uint64_t)len;
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}
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/* see bearssl_aead.h */
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void
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br_gcm_flip(br_gcm_context *ctx)
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{
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/*
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* We complete the GHASH computation if there is a partial block.
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* The GHASH implementation automatically applies padding with
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* zeros.
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*/
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size_t ptr;
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ptr = (size_t)ctx->count_aad & (size_t)15;
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if (ptr != 0) {
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ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
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}
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}
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/* see bearssl_aead.h */
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void
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br_gcm_run(br_gcm_context *ctx, int encrypt, void *data, size_t len)
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{
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unsigned char *buf;
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size_t ptr, dlen;
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buf = data;
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ptr = (size_t)ctx->count_ctr & (size_t)15;
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if (ptr != 0) {
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/*
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* If we have a partial block, then we try to complete it.
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*/
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size_t u, clen;
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clen = 16 - ptr;
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if (len < clen) {
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clen = len;
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}
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for (u = 0; u < clen; u ++) {
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unsigned x, y;
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x = buf[u];
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y = x ^ ctx->buf[ptr + u];
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ctx->buf[ptr + u] = encrypt ? y : x;
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buf[u] = y;
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}
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ctx->count_ctr += (uint64_t)clen;
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buf += clen;
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len -= clen;
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if (ptr + clen < 16) {
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return;
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}
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ctx->gh(ctx->y, ctx->h, ctx->buf, 16);
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}
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/*
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* Process full blocks.
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*/
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dlen = len & ~(size_t)15;
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if (!encrypt) {
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ctx->gh(ctx->y, ctx->h, buf, dlen);
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}
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ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->jc, buf, dlen);
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if (encrypt) {
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ctx->gh(ctx->y, ctx->h, buf, dlen);
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}
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buf += dlen;
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len -= dlen;
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ctx->count_ctr += (uint64_t)dlen;
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if (len > 0) {
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/*
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* There is a partial block.
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*/
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size_t u;
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memset(ctx->buf, 0, sizeof ctx->buf);
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ctx->jc = (*ctx->bctx)->run(ctx->bctx, ctx->j0_1,
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ctx->jc, ctx->buf, 16);
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for (u = 0; u < len; u ++) {
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unsigned x, y;
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x = buf[u];
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y = x ^ ctx->buf[u];
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ctx->buf[u] = encrypt ? y : x;
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buf[u] = y;
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}
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ctx->count_ctr += (uint64_t)len;
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}
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}
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/* see bearssl_aead.h */
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void
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br_gcm_get_tag(br_gcm_context *ctx, void *tag)
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{
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size_t ptr;
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unsigned char tmp[16];
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ptr = (size_t)ctx->count_ctr & (size_t)15;
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if (ptr > 0) {
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/*
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* There is a partial block: encrypted/decrypted data has
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* been produced, but the encrypted bytes must still be
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* processed by GHASH.
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*/
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ctx->gh(ctx->y, ctx->h, ctx->buf, ptr);
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}
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/*
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* Final block for GHASH: the AAD and plaintext lengths (in bits).
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*/
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br_enc64be(tmp, ctx->count_aad << 3);
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br_enc64be(tmp + 8, ctx->count_ctr << 3);
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ctx->gh(ctx->y, ctx->h, tmp, 16);
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/*
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* Tag is the GHASH output XORed with the encryption of the
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* nonce with the initial counter value.
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*/
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memcpy(tag, ctx->y, 16);
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(*ctx->bctx)->run(ctx->bctx, ctx->j0_1, ctx->j0_2, tag, 16);
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}
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/* see bearssl_aead.h */
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uint32_t
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br_gcm_check_tag(br_gcm_context *ctx, const void *tag)
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{
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unsigned char tmp[16];
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size_t u;
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int x;
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br_gcm_get_tag(ctx, tmp);
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x = 0;
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for (u = 0; u < sizeof tmp; u ++) {
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x |= tmp[u] ^ ((const unsigned char *)tag)[u];
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}
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return EQ0(x);
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}
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/* see bearssl_aead.h */
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const br_aead_class br_gcm_vtable = {
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16,
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(void (*)(const br_aead_class **, const void *, size_t))
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&br_gcm_reset,
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(void (*)(const br_aead_class **, const void *, size_t))
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&br_gcm_aad_inject,
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(void (*)(const br_aead_class **))
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&br_gcm_flip,
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(void (*)(const br_aead_class **, int, void *, size_t))
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&br_gcm_run,
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(void (*)(const br_aead_class **, void *))
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&br_gcm_get_tag,
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(uint32_t (*)(const br_aead_class **, const void *))
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&br_gcm_check_tag
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};
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