ssl_rec_ccm.c

/*
 * Copyright (c) 2018 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"

/*
 * CCM initialisation. This does everything except setting the vtable,
 * which depends on whether this is a context for encrypting or for
 * decrypting.
 */
static void
gen_ccm_init(br_sslrec_ccm_context *cc,
	const br_block_ctrcbc_class *bc_impl,
	const void *key, size_t key_len,
	const void *iv, size_t tag_len)
{
	cc->seq = 0;
	bc_impl->init(&cc->bc.vtable, key, key_len);
	memcpy(cc->iv, iv, sizeof cc->iv);
	cc->tag_len = tag_len;
}

static void
in_ccm_init(br_sslrec_ccm_context *cc,
	const br_block_ctrcbc_class *bc_impl,
	const void *key, size_t key_len,
	const void *iv, size_t tag_len)
{
	cc->vtable.in = &br_sslrec_in_ccm_vtable;
	gen_ccm_init(cc, bc_impl, key, key_len, iv, tag_len);
}

static int
ccm_check_length(const br_sslrec_ccm_context *cc, size_t rlen)
{
	/*
	 * CCM overhead is 8 bytes for nonce_explicit, and the tag
	 * (normally 8 or 16 bytes, depending on cipher suite).
	 */
	size_t over;

	over = 8 + cc->tag_len;
	return rlen >= over && rlen <= (16384 + over);
}

static unsigned char *
ccm_decrypt(br_sslrec_ccm_context *cc,
	int record_type, unsigned version, void *data, size_t *data_len)
{
	br_ccm_context zc;
	unsigned char *buf;
	unsigned char nonce[12], header[13];
	size_t len;

	buf = (unsigned char *)data + 8;
	len = *data_len - (8 + cc->tag_len);

	/*
	 * Make nonce (implicit + explicit parts).
	 */
	memcpy(nonce, cc->iv, sizeof cc->iv);
	memcpy(nonce + 4, data, 8);

	/*
	 * Assemble synthetic header for the AAD.
	 */
	br_enc64be(header, cc->seq ++);
	header[8] = (unsigned char)record_type;
	br_enc16be(header + 9, version);
	br_enc16be(header + 11, len);

	/*
	 * Perform CCM decryption.
	 */
	br_ccm_init(&zc, &cc->bc.vtable);
	br_ccm_reset(&zc, nonce, sizeof nonce, sizeof header, len, cc->tag_len);
	br_ccm_aad_inject(&zc, header, sizeof header);
	br_ccm_flip(&zc);
	br_ccm_run(&zc, 0, buf, len);
	if (!br_ccm_check_tag(&zc, buf + len)) {
		return NULL;
	}
	*data_len = len;
	return buf;
}

/* see bearssl_ssl.h */
const br_sslrec_in_ccm_class br_sslrec_in_ccm_vtable = {
	{
		sizeof(br_sslrec_ccm_context),
		(int (*)(const br_sslrec_in_class *const *, size_t))
			&ccm_check_length,
		(unsigned char *(*)(const br_sslrec_in_class **,
			int, unsigned, void *, size_t *))
			&ccm_decrypt
	},
	(void (*)(const br_sslrec_in_ccm_class **,
		const br_block_ctrcbc_class *, const void *, size_t,
		const void *, size_t))
		&in_ccm_init
};

static void
out_ccm_init(br_sslrec_ccm_context *cc,
	const br_block_ctrcbc_class *bc_impl,
	const void *key, size_t key_len,
	const void *iv, size_t tag_len)
{
	cc->vtable.out = &br_sslrec_out_ccm_vtable;
	gen_ccm_init(cc, bc_impl, key, key_len, iv, tag_len);
}

static void
ccm_max_plaintext(const br_sslrec_ccm_context *cc,
	size_t *start, size_t *end)
{
	size_t len;

	*start += 8;
	len = *end - *start - cc->tag_len;
	if (len > 16384) {
		len = 16384;
	}
	*end = *start + len;
}

static unsigned char *
ccm_encrypt(br_sslrec_ccm_context *cc,
	int record_type, unsigned version, void *data, size_t *data_len)
{
	br_ccm_context zc;
	unsigned char *buf;
	unsigned char nonce[12], header[13];
	size_t len;

	buf = (unsigned char *)data;
	len = *data_len;

	/*
	 * Make nonce; the explicit part is an encoding of the sequence
	 * number.
	 */
	memcpy(nonce, cc->iv, sizeof cc->iv);
	br_enc64be(nonce + 4, cc->seq);

	/*
	 * Assemble synthetic header for the AAD.
	 */
	br_enc64be(header, cc->seq ++);
	header[8] = (unsigned char)record_type;
	br_enc16be(header + 9, version);
	br_enc16be(header + 11, len);

	/*
	 * Perform CCM encryption.
	 */
	br_ccm_init(&zc, &cc->bc.vtable);
	br_ccm_reset(&zc, nonce, sizeof nonce, sizeof header, len, cc->tag_len);
	br_ccm_aad_inject(&zc, header, sizeof header);
	br_ccm_flip(&zc);
	br_ccm_run(&zc, 1, buf, len);
	br_ccm_get_tag(&zc, buf + len);

	/*
	 * Assemble header and adjust pointer/length.
	 */
	len += 8 + cc->tag_len;
	buf -= 13;
	memcpy(buf + 5, nonce + 4, 8);
	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_ccm_class br_sslrec_out_ccm_vtable = {
	{
		sizeof(br_sslrec_ccm_context),
		(void (*)(const br_sslrec_out_class *const *,
			size_t *, size_t *))
			&ccm_max_plaintext,
		(unsigned char *(*)(const br_sslrec_out_class **,
			int, unsigned, void *, size_t *))
			&ccm_encrypt
	},
	(void (*)(const br_sslrec_out_ccm_class **,
		const br_block_ctrcbc_class *, const void *, size_t,
		const void *, size_t))
		&out_ccm_init
};