/*

 * HMAC-SHA256 KDF (RFC 5295) and HKDF-Expand(SHA256) (RFC 5869)

 * Copyright (c) 2014-2017, Jouni Malinen <j@w1.fi>

 *

 * This software may be distributed under the terms of the BSD license.

 * See README for more details.

 */

#include "includes.h"

#include "common.h"

#include "sha256.h"

/**

 * hmac_sha256_kdf - HMAC-SHA256 based KDF (RFC 5295)

 * @secret: Key for KDF

 * @secret_len: Length of the key in bytes

 * @label: A unique label for each purpose of the KDF or %NULL to select

 *  RFC 5869 HKDF-Expand() with arbitrary seed (= info)

 * @seed: Seed value to bind into the key

 * @seed_len: Length of the seed

 * @out: Buffer for the generated pseudo-random key

 * @outlen: Number of bytes of key to generate

 * Returns: 0 on success, -1 on failure.

 *

 * This function is used to derive new, cryptographically separate keys from a

 * given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2. When used

 * with label = NULL and seed = info, this matches HKDF-Expand() defined in

 * RFC 5869, Chapter 2.3.

 */

int hmac_sha256_kdf(const u8 *secret, size_t secret_len,

        const char *label, const u8 *seed, size_t seed_len,

        u8 *out, size_t outlen)

{

  u8 T[SHA256_MAC_LEN];

  u8 iter = 1;

  const unsigned char *addr[4];

  size_t len[4];

  size_t pos, clen;

  addr[0] = T;

  len[0] = SHA256_MAC_LEN;

  if (label) {

    addr[1] = (const unsigned char *) label;

    len[1] = os_strlen(label) + 1;

  } else {

    addr[1] = (const u8 *) "";

    len[1] = 0;

  }

  addr[2] = seed;

  len[2] = seed_len;

  addr[3] = &iter;

  len[3] = 1;

  if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0)

    return -1;

  pos = 0;

  for (;;) {

    clen = outlen - pos;

    if (clen > SHA256_MAC_LEN)

      clen = SHA256_MAC_LEN;

    os_memcpy(out + pos, T, clen);

    pos += clen;

    if (pos == outlen)

      break;

    if (iter == 255) {

      os_memset(out, 0, outlen);

      forced_memzero(T, SHA256_MAC_LEN);

      return -1;

    }

    iter++;

    if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)

    {

      os_memset(out, 0, outlen);

      forced_memzero(T, SHA256_MAC_LEN);

      return -1;

    }

  }

  forced_memzero(T, SHA256_MAC_LEN);

  return 0;

}