hkdf.c

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    1 /*
    2  * CDDL HEADER START
    3  *
    4  * This file and its contents are supplied under the terms of the
    5  * Common Development and Distribution License ("CDDL"), version 1.0.
    6  * You may only use this file in accordance with the terms of version
    7  * 1.0 of the CDDL.
    8  *
    9  * A full copy of the text of the CDDL should have accompanied this
   10  * source.  A copy of the CDDL is also available via the Internet at
   11  * http://www.illumos.org/license/CDDL.
   12  *
   13  * CDDL HEADER END
   14  */
   15 
   16 /*
   17  * Copyright (c) 2017, Datto, Inc. All rights reserved.
   18  */
   19 
   20 #include <sys/dmu.h>
   21 #include <sys/hkdf.h>
   22 #include <sys/freebsd_crypto.h>
   23 #include <sys/hkdf.h>
   24 
   25 static int
   26 hkdf_sha512_extract(uint8_t *salt, uint_t salt_len, uint8_t *key_material,
   27     uint_t km_len, uint8_t *out_buf)
   28 {
   29         crypto_key_t key;
   30 
   31         /* initialize the salt as a crypto key */
   32         key.ck_length = CRYPTO_BYTES2BITS(salt_len);
   33         key.ck_data = salt;
   34 
   35         crypto_mac(&key, key_material, km_len, out_buf, SHA512_DIGEST_LENGTH);
   36 
   37         return (0);
   38 }
   39 
   40 static int
   41 hkdf_sha512_expand(uint8_t *extract_key, uint8_t *info, uint_t info_len,
   42     uint8_t *out_buf, uint_t out_len)
   43 {
   44         struct hmac_ctx ctx;
   45         crypto_key_t key;
   46         uint_t i, T_len = 0, pos = 0;
   47         uint8_t c;
   48         uint_t N = (out_len + SHA512_DIGEST_LENGTH) / SHA512_DIGEST_LENGTH;
   49         uint8_t T[SHA512_DIGEST_LENGTH];
   50 
   51         if (N > 255)
   52                 return (SET_ERROR(EINVAL));
   53 
   54         /* initialize the salt as a crypto key */
   55         key.ck_length = CRYPTO_BYTES2BITS(SHA512_DIGEST_LENGTH);
   56         key.ck_data = extract_key;
   57 
   58         for (i = 1; i <= N; i++) {
   59                 c = i;
   60 
   61                 crypto_mac_init(&ctx, &key);
   62                 crypto_mac_update(&ctx, T, T_len);
   63                 crypto_mac_update(&ctx, info, info_len);
   64                 crypto_mac_update(&ctx, &c, 1);
   65                 crypto_mac_final(&ctx, T, SHA512_DIGEST_LENGTH);
   66                 memcpy(out_buf + pos, T,
   67                     (i != N) ? SHA512_DIGEST_LENGTH : (out_len - pos));
   68                 pos += SHA512_DIGEST_LENGTH;
   69         }
   70 
   71         return (0);
   72 }
   73 
   74 /*
   75  * HKDF is designed to be a relatively fast function for deriving keys from a
   76  * master key + a salt. We use this function to generate new encryption keys
   77  * so as to avoid hitting the cryptographic limits of the underlying
   78  * encryption modes. Note that, for the sake of deriving encryption keys, the
   79  * info parameter is called the "salt" everywhere else in the code.
   80  */
   81 int
   82 hkdf_sha512(uint8_t *key_material, uint_t km_len, uint8_t *salt,
   83     uint_t salt_len, uint8_t *info, uint_t info_len, uint8_t *output_key,
   84     uint_t out_len)
   85 {
   86         int ret;
   87         uint8_t extract_key[SHA512_DIGEST_LENGTH];
   88 
   89         ret = hkdf_sha512_extract(salt, salt_len, key_material, km_len,
   90             extract_key);
   91         if (ret != 0)
   92                 return (ret);
   93 
   94         ret = hkdf_sha512_expand(extract_key, info, info_len, output_key,
   95             out_len);
   96         if (ret != 0)
   97                 return (ret);
   98 
   99         return (0);
  100 }

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FreeBSD/Linux Kernel Cross Reference sys/contrib/openzfs/module/os/freebsd/zfs/hkdf.c

FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/os/freebsd/zfs/hkdf.c