hkdf.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"

const unsigned char br_hkdf_no_salt = 0;

/* see bearssl_kdf.h */
void
br_hkdf_init(br_hkdf_context *hc, const br_hash_class *digest_vtable,
	const void *salt, size_t salt_len)
{
	br_hmac_key_context kc;
	unsigned char tmp[64];

	if (salt == BR_HKDF_NO_SALT) {
		salt = tmp;
		salt_len = br_digest_size(digest_vtable);
		memset(tmp, 0, salt_len);
	}
	br_hmac_key_init(&kc, digest_vtable, salt, salt_len);
	br_hmac_init(&hc->u.hmac_ctx, &kc, 0);
	hc->dig_len = br_hmac_size(&hc->u.hmac_ctx);
}

/* see bearssl_kdf.h */
void
br_hkdf_inject(br_hkdf_context *hc, const void *ikm, size_t ikm_len)
{
	br_hmac_update(&hc->u.hmac_ctx, ikm, ikm_len);
}

/* see bearssl_kdf.h */
void
br_hkdf_flip(br_hkdf_context *hc)
{
	unsigned char tmp[64];

	br_hmac_out(&hc->u.hmac_ctx, tmp);
	br_hmac_key_init(&hc->u.prk_ctx,
		br_hmac_get_digest(&hc->u.hmac_ctx), tmp, hc->dig_len);
	hc->ptr = hc->dig_len;
	hc->chunk_num = 0;
}

/* see bearssl_kdf.h */
size_t
br_hkdf_produce(br_hkdf_context *hc,
	const void *info, size_t info_len, void *out, size_t out_len)
{
	size_t tlen;

	tlen = 0;
	while (out_len > 0) {
		size_t clen;

		if (hc->ptr == hc->dig_len) {
			br_hmac_context hmac_ctx;
			unsigned char x;

			hc->chunk_num ++;
			if (hc->chunk_num == 256) {
				return tlen;
			}
			x = hc->chunk_num;
			br_hmac_init(&hmac_ctx, &hc->u.prk_ctx, 0);
			if (x != 1) {
				br_hmac_update(&hmac_ctx, hc->buf, hc->dig_len);
			}
			br_hmac_update(&hmac_ctx, info, info_len);
			br_hmac_update(&hmac_ctx, &x, 1);
			br_hmac_out(&hmac_ctx, hc->buf);
			hc->ptr = 0;
		}
		clen = hc->dig_len - hc->ptr;
		if (clen > out_len) {
			clen = out_len;
		}
		memcpy(out, hc->buf + hc->ptr, clen);
		out = (unsigned char *)out + clen;
		out_len -= clen;
		hc->ptr += clen;
		tlen += clen;
	}
	return tlen;
}