/*

 *  HKDF implementation -- RFC 5869

 *

 *  Copyright The Mbed TLS Contributors

 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later

 */

#include "common.h"

#if defined(MBEDTLS_HKDF_C)

#include <string.h>

#include "mbedtls/hkdf.h"

#include "mbedtls/platform_util.h"

#include "mbedtls/error.h"

int mbedtls_hkdf(const mbedtls_md_info_t *md, const unsigned char *salt,

                 size_t salt_len, const unsigned char *ikm, size_t ikm_len,

                 const unsigned char *info, size_t info_len,

                 unsigned char *okm, size_t okm_len)

{

    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;

    unsigned char prk[MBEDTLS_MD_MAX_SIZE];

    ret = mbedtls_hkdf_extract(md, salt, salt_len, ikm, ikm_len, prk);

    if (ret == 0) {

        ret = mbedtls_hkdf_expand(md, prk, mbedtls_md_get_size(md),

                                  info, info_len, okm, okm_len);

    }

    mbedtls_platform_zeroize(prk, sizeof(prk));

    return ret;

}

int mbedtls_hkdf_extract(const mbedtls_md_info_t *md,

                         const unsigned char *salt, size_t salt_len,

                         const unsigned char *ikm, size_t ikm_len,

                         unsigned char *prk)

{

    unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' };

    if (salt == NULL) {

        size_t hash_len;

        if (salt_len != 0) {

            return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;

        }

        hash_len = mbedtls_md_get_size(md);

        if (hash_len == 0) {

            return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;

        }

        salt = null_salt;

        salt_len = hash_len;

    }

    return mbedtls_md_hmac(md, salt, salt_len, ikm, ikm_len, prk);

}

int mbedtls_hkdf_expand(const mbedtls_md_info_t *md, const unsigned char *prk,

                        size_t prk_len, const unsigned char *info,

                        size_t info_len, unsigned char *okm, size_t okm_len)

{

    size_t hash_len;

    size_t where = 0;

    size_t n;

    size_t t_len = 0;

    size_t i;

    int ret = 0;

    mbedtls_md_context_t ctx;

    unsigned char t[MBEDTLS_MD_MAX_SIZE];

    if (okm == NULL) {

        return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;

    }

    hash_len = mbedtls_md_get_size(md);

    if (prk_len < hash_len || hash_len == 0) {

        return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;

    }

    if (info == NULL) {

        info = (const unsigned char *) "";

        info_len = 0;

    }

    n = okm_len / hash_len;

    if (okm_len % hash_len != 0) {

        n++;

    }

    /*

     * Per RFC 5869 Section 2.3, okm_len must not exceed

     * 255 times the hash length

     */

    if (n > 255) {

        return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;

    }

    mbedtls_md_init(&ctx);

    if ((ret = mbedtls_md_setup(&ctx, md, 1)) != 0) {

        goto exit;

    }

    memset(t, 0, hash_len);

    /*

     * Compute T = T(1) | T(2) | T(3) | ... | T(N)

     * Where T(N) is defined in RFC 5869 Section 2.3

     */

    for (i = 1; i <= n; i++) {

        size_t num_to_copy;

        unsigned char c = i & 0xff;

        ret = mbedtls_md_hmac_starts(&ctx, prk, prk_len);

        if (ret != 0) {

            goto exit;

        }

        ret = mbedtls_md_hmac_update(&ctx, t, t_len);

        if (ret != 0) {

            goto exit;

        }

        ret = mbedtls_md_hmac_update(&ctx, info, info_len);

        if (ret != 0) {

            goto exit;

        }

        /* The constant concatenated to the end of each T(n) is a single octet.

         * */

        ret = mbedtls_md_hmac_update(&ctx, &c, 1);

        if (ret != 0) {

            goto exit;

        }

        ret = mbedtls_md_hmac_finish(&ctx, t);

        if (ret != 0) {

            goto exit;

        }

        num_to_copy = i != n ? hash_len : okm_len - where;

        memcpy(okm + where, t, num_to_copy);

        where += hash_len;

        t_len = hash_len;

    }

exit:

    mbedtls_md_free(&ctx);

    mbedtls_platform_zeroize(t, sizeof(t));

    return ret;

}

#endif /* MBEDTLS_HKDF_C */