aes_ct_cbcdec.c

/*
 * Copyright (c) 2016 Thomas Pornin <[email protected]>
 *
 * 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"

/* see bearssl_block.h */
void
br_aes_ct_cbcdec_init(br_aes_ct_cbcdec_keys *ctx,
	const void *key, size_t len)
{
	ctx->vtable = &br_aes_ct_cbcdec_vtable;
	ctx->num_rounds = br_aes_ct_keysched(ctx->skey, key, len);
}

/* see bearssl_block.h */
void
br_aes_ct_cbcdec_run(const br_aes_ct_cbcdec_keys *ctx,
	void *iv, void *data, size_t len)
{
	unsigned char *buf, *ivbuf;
	uint32_t iv0, iv1, iv2, iv3;
	uint32_t sk_exp[120];

	br_aes_ct_skey_expand(sk_exp, ctx->num_rounds, ctx->skey);
	ivbuf = iv;
	iv0 = br_dec32le(ivbuf);
	iv1 = br_dec32le(ivbuf + 4);
	iv2 = br_dec32le(ivbuf + 8);
	iv3 = br_dec32le(ivbuf + 12);
	buf = data;
	while (len > 0) {
		uint32_t q[8], sq[8];

		q[0] = br_dec32le(buf);
		q[2] = br_dec32le(buf + 4);
		q[4] = br_dec32le(buf + 8);
		q[6] = br_dec32le(buf + 12);
		if (len >= 32) {
			q[1] = br_dec32le(buf + 16);
			q[3] = br_dec32le(buf + 20);
			q[5] = br_dec32le(buf + 24);
			q[7] = br_dec32le(buf + 28);
		} else {
			q[1] = 0;
			q[3] = 0;
			q[5] = 0;
			q[7] = 0;
		}
		memcpy(sq, q, sizeof q);
		br_aes_ct_ortho(q);
		br_aes_ct_bitslice_decrypt(ctx->num_rounds, sk_exp, q);
		br_aes_ct_ortho(q);
		br_enc32le(buf, q[0] ^ iv0);
		br_enc32le(buf + 4, q[2] ^ iv1);
		br_enc32le(buf + 8, q[4] ^ iv2);
		br_enc32le(buf + 12, q[6] ^ iv3);
		if (len < 32) {
			iv0 = sq[0];
			iv1 = sq[2];
			iv2 = sq[4];
			iv3 = sq[6];
			break;
		}
		br_enc32le(buf + 16, q[1] ^ sq[0]);
		br_enc32le(buf + 20, q[3] ^ sq[2]);
		br_enc32le(buf + 24, q[5] ^ sq[4]);
		br_enc32le(buf + 28, q[7] ^ sq[6]);
		iv0 = sq[1];
		iv1 = sq[3];
		iv2 = sq[5];
		iv3 = sq[7];
		buf += 32;
		len -= 32;
	}
	br_enc32le(ivbuf, iv0);
	br_enc32le(ivbuf + 4, iv1);
	br_enc32le(ivbuf + 8, iv2);
	br_enc32le(ivbuf + 12, iv3);
}

/* see bearssl_block.h */
const br_block_cbcdec_class br_aes_ct_cbcdec_vtable = {
	sizeof(br_aes_ct_cbcdec_keys),
	16,
	4,
	(void (*)(const br_block_cbcdec_class **, const void *, size_t))
		&br_aes_ct_cbcdec_init,
	(void (*)(const br_block_cbcdec_class *const *, void *, void *, size_t))
		&br_aes_ct_cbcdec_run
};