/* $OpenBSD: hkdf.c,v 1.7 2021/12/12 21:30:14 tb Exp $ */
/* Copyright (c) 2014, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <openssl/hkdf.h>

#include <string.h>

#include <openssl/err.h>
#include <openssl/hmac.h>

#include "evp_locl.h"
#include "hmac_local.h"

/* https://tools.ietf.org/html/rfc5869#section-2 */
int
HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
    const uint8_t *secret, size_t secret_len, const uint8_t *salt,
    size_t salt_len, const uint8_t *info, size_t info_len)
{
        uint8_t prk[EVP_MAX_MD_SIZE];
        size_t prk_len;

        if (!HKDF_extract(prk, &prk_len, digest, secret, secret_len, salt,
            salt_len))
                return 0;
        if (!HKDF_expand(out_key, out_len, digest, prk, prk_len, info,
            info_len))
                return 0;

        return 1;
}

/* https://tools.ietf.org/html/rfc5869#section-2.2 */
int
HKDF_extract(uint8_t *out_key, size_t *out_len,
    const EVP_MD *digest, const uint8_t *secret, size_t secret_len,
    const uint8_t *salt, size_t salt_len)
{
        unsigned int len;

        /*
         * If salt is not given, HashLength zeros are used. However, HMAC does
         * that internally already so we can ignore it.
         */
        if (HMAC(digest, salt, salt_len, secret, secret_len, out_key, &len) ==
            NULL) {
                CRYPTOerror(ERR_R_CRYPTO_LIB);
                return 0;
        }
        *out_len = len;
        return 1;
}

/* https://tools.ietf.org/html/rfc5869#section-2.3 */
int
HKDF_expand(uint8_t *out_key, size_t out_len,
    const EVP_MD *digest, const uint8_t *prk, size_t prk_len,
    const uint8_t *info, size_t info_len)
{
        const size_t digest_len = EVP_MD_size(digest);
        uint8_t previous[EVP_MAX_MD_SIZE];
        size_t n, done = 0;
        unsigned int i;
        int ret = 0;
        HMAC_CTX hmac;

        /* Expand key material to desired length. */
        n = (out_len + digest_len - 1) / digest_len;
        if (out_len + digest_len < out_len || n > 255) {
                CRYPTOerror(EVP_R_TOO_LARGE);
                return 0;
        }

        HMAC_CTX_init(&hmac);
        if (!HMAC_Init_ex(&hmac, prk, prk_len, digest, NULL))
                goto out;

        for (i = 0; i < n; i++) {
                uint8_t ctr = i + 1;
                size_t todo;

                if (i != 0 && (!HMAC_Init_ex(&hmac, NULL, 0, NULL, NULL) ||
                    !HMAC_Update(&hmac, previous, digest_len)))
                        goto out;

                if (!HMAC_Update(&hmac, info, info_len) ||
                    !HMAC_Update(&hmac, &ctr, 1) ||
                    !HMAC_Final(&hmac, previous, NULL))
                        goto out;

                todo = digest_len;
                if (done + todo > out_len)
                        todo = out_len - done;

                memcpy(out_key + done, previous, todo);
                done += todo;
        }

        ret = 1;

 out:
        HMAC_CTX_cleanup(&hmac);
        explicit_bzero(previous, sizeof(previous));
        if (ret != 1)
                CRYPTOerror(ERR_R_CRYPTO_LIB);
        return ret;
}