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/*
* cifra - embedded cryptography library
* Written in 2014 by Joseph Birr-Pixton <jpixton@gmail.com>
*
* To the extent possible under law, the author(s) have dedicated all
* copyright and related and neighboring rights to this software to the
* public domain worldwide. This software is distributed without any
* warranty.
*
* You should have received a copy of the CC0 Public Domain Dedication
* along with this software. If not, see
* <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
#include "handy.h"
#include "prp.h"
#include "modes.h"
#include "blockwise.h"
#include "bitops.h"
#include "gf128.h"
#include "tassert.h"
#include <string.h>
#define STATE_INVALID 0
#define STATE_AAD 1
#define STATE_CIPHER 2
static void ghash_init(ghash_ctx *ctx, uint8_t H[16])
{
memset(ctx, 0, sizeof *ctx);
cf_gf128_frombytes_be(H, ctx->H);
ctx->state = STATE_AAD;
}
static void ghash_block(void *vctx, const uint8_t *data)
{
ghash_ctx *ctx = vctx;
cf_gf128 gfdata;
cf_gf128_frombytes_be(data, gfdata);
cf_gf128_add(gfdata, ctx->Y, ctx->Y);
cf_gf128_mul(ctx->Y, ctx->H, ctx->Y);
}
static void ghash_add(ghash_ctx *ctx, const uint8_t *buf, size_t n)
{
cf_blockwise_accumulate(ctx->buffer, &ctx->buffer_used,
sizeof ctx->buffer,
buf, n,
ghash_block,
ctx);
}
static void ghash_add_pad(ghash_ctx *ctx)
{
if (ctx->buffer_used == 0)
return;
memset(ctx->buffer + ctx->buffer_used, 0, sizeof(ctx->buffer) - ctx->buffer_used);
ghash_block(ctx, ctx->buffer);
ctx->buffer_used = 0;
}
static void ghash_add_aad(ghash_ctx *ctx, const uint8_t *buf, size_t n)
{
assert(ctx->state == STATE_AAD);
ctx->len_aad += n;
ghash_add(ctx, buf, n);
}
static void ghash_add_cipher(ghash_ctx *ctx, const uint8_t *buf, size_t n)
{
if (ctx->state == STATE_AAD)
{
ghash_add_pad(ctx);
ctx->state = STATE_CIPHER;
}
assert(ctx->state == STATE_CIPHER);
ctx->len_cipher += n;
ghash_add(ctx, buf, n);
}
static void ghash_final(ghash_ctx *ctx, uint8_t out[16])
{
uint8_t lenbuf[8];
if (ctx->state == STATE_AAD || ctx->state == STATE_CIPHER)
{
ghash_add_pad(ctx);
ctx->state = STATE_INVALID;
}
/* Add len(A) || len(C) */
write64_be(ctx->len_aad * 8, lenbuf);
ghash_add(ctx, lenbuf, sizeof lenbuf);
write64_be(ctx->len_cipher * 8, lenbuf);
ghash_add(ctx, lenbuf, sizeof lenbuf);
assert(ctx->buffer_used == 0);
cf_gf128_tobytes_be(ctx->Y, out);
}
void cf_gcm_encrypt_init(const cf_prp *prp, void *prpctx, cf_gcm_ctx *gcmctx,
const uint8_t *header, size_t nheader,
const uint8_t *nonce, size_t nnonce)
{
uint8_t H[16] = { 0 };
/* H = E_K(0^128) */
prp->encrypt(prpctx, H, H);
/* Produce CTR nonce, Y_0:
*
* if len(IV) == 96
* Y_0 = IV || 0^31 || 1
* otherwise
* Y_0 = GHASH(H, {}, IV)
*/
if (nnonce == 12)
{
memcpy(gcmctx->Y0, nonce, nnonce);
gcmctx->Y0[12] = gcmctx->Y0[13] = gcmctx->Y0[14] = 0x00;
gcmctx->Y0[15] = 0x01;
} else {
ghash_init(&gcmctx->gh, H);
ghash_add_cipher(&gcmctx->gh, nonce, nnonce);
ghash_final(&gcmctx->gh, gcmctx->Y0);
}
/* Hash AAD */
ghash_init(&gcmctx->gh, H);
ghash_add_aad(&gcmctx->gh, header, nheader);
/* Produce ciphertext */
memset(gcmctx->e_Y0, 0, sizeof(gcmctx->e_Y0));
cf_ctr_init(&gcmctx->ctr, prp, prpctx, gcmctx->Y0);
cf_ctr_custom_counter(&gcmctx->ctr, 12, 4); /* counter is 2^32 */
cf_ctr_cipher(&gcmctx->ctr, gcmctx->e_Y0, gcmctx->e_Y0, sizeof gcmctx->e_Y0); /* first block is tag offset */
mem_clean(H, sizeof H);
}
void cf_gcm_encrypt_update(cf_gcm_ctx *gcmctx, const uint8_t *plain, size_t nplain, uint8_t *cipher)
{
cf_ctr_cipher(&gcmctx->ctr, plain, cipher, nplain);
ghash_add_cipher(&gcmctx->gh, cipher, nplain);
}
void cf_gcm_encrypt_final(cf_gcm_ctx *gcmctx, uint8_t *tag, size_t ntag)
{
/* Post-process ghash output */
uint8_t full_tag[16] = { 0 };
ghash_final(&gcmctx->gh, full_tag);
assert(ntag > 1 && ntag <= 16);
xor_bb(tag, full_tag, gcmctx->e_Y0, ntag);
mem_clean(full_tag, sizeof full_tag);
mem_clean(gcmctx, sizeof *gcmctx);
}
void cf_gcm_encrypt(const cf_prp *prp, void *prpctx,
const uint8_t *plain, size_t nplain,
const uint8_t *header, size_t nheader,
const uint8_t *nonce, size_t nnonce,
uint8_t *cipher, /* the same size as nplain */
uint8_t *tag, size_t ntag)
{
cf_gcm_ctx gcmctx;
cf_gcm_encrypt_init(prp, prpctx, &gcmctx, header, nheader, nonce, nnonce);
cf_gcm_encrypt_update(&gcmctx, plain, nplain, cipher);
cf_gcm_encrypt_final(&gcmctx, tag, ntag);
}
int cf_gcm_decrypt(const cf_prp *prp, void *prpctx,
const uint8_t *cipher, size_t ncipher,
const uint8_t *header, size_t nheader,
const uint8_t *nonce, size_t nnonce,
const uint8_t *tag, size_t ntag,
uint8_t *plain)
{
uint8_t H[16] = { 0 };
uint8_t Y0[16];
/* H = E_K(0^128) */
prp->encrypt(prpctx, H, H);
/* Produce CTR nonce, Y_0:
*
* if len(IV) == 96
* Y_0 = IV || 0^31 || 1
* otherwise
* Y_0 = GHASH(H, {}, IV)
*/
if (nnonce == 12)
{
memcpy(Y0, nonce, nnonce);
Y0[12] = Y0[13] = Y0[14] = 0x00;
Y0[15] = 0x01;
} else {
ghash_ctx gh;
ghash_init(&gh, H);
ghash_add_cipher(&gh, nonce, nnonce);
ghash_final(&gh, Y0);
}
/* Hash AAD. */
ghash_ctx gh;
ghash_init(&gh, H);
ghash_add_aad(&gh, header, nheader);
/* Start counter mode, to obtain offset on tag. */
uint8_t e_Y0[16] = { 0 };
cf_ctr ctr;
cf_ctr_init(&ctr, prp, prpctx, Y0);
cf_ctr_custom_counter(&ctr, 12, 4);
cf_ctr_cipher(&ctr, e_Y0, e_Y0, sizeof e_Y0);
/* Hash ciphertext. */
ghash_add_cipher(&gh, cipher, ncipher);
/* Produce tag. */
uint8_t full_tag[16];
ghash_final(&gh, full_tag);
assert(ntag > 1 && ntag <= 16);
xor_bb(full_tag, full_tag, e_Y0, ntag);
int err = 1;
if (!mem_eq(full_tag, tag, ntag))
goto x_err;
/* Complete decryption. */
cf_ctr_cipher(&ctr, cipher, plain, ncipher);
err = 0;
x_err:
mem_clean(H, sizeof H);
mem_clean(Y0, sizeof Y0);
mem_clean(e_Y0, sizeof e_Y0);
mem_clean(full_tag, sizeof full_tag);
mem_clean(&gh, sizeof gh);
mem_clean(&ctr, sizeof ctr);
return err;
}
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