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SCRYPT(7)                           OpenSSL                          SCRYPT(7)



NAME
       scrypt - EVP_PKEY scrypt KDF support

DESCRIPTION
       The EVP_PKEY_SCRYPT algorithm implements the scrypt password based key
       derivation function, as described in RFC 7914.  It is memory-hard in
       the sense that it deliberately requires a significant amount of RAM for
       efficient computation. The intention of this is to render brute forcing
       of passwords on systems that lack large amounts of main memory (such as
       GPUs or ASICs) computationally infeasible.

       scrypt provides three work factors that can be customized: N, r and p.
       N, which has to be a positive power of two, is the general work factor
       and scales CPU time in an approximately linear fashion. r is the block
       size of the internally used hash function and p is the parallelization
       factor. Both r and p need to be greater than zero. The amount of RAM
       that scrypt requires for its computation is roughly (128 * N * r * p)
       bytes.

       In the original paper of Colin Percival ("Stronger Key Derivation via
       Sequential Memory-Hard Functions", 2009), the suggested values that
       give a computation time of less than 5 seconds on a 2.5 GHz Intel Core
       2 Duo are N = 2^20 = 1048576, r = 8, p = 1. Consequently, the required
       amount of memory for this computation is roughly 1 GiB. On a more
       recent CPU (Intel i7-5930K at 3.5 GHz), this computation takes about 3
       seconds. When N, r or p are not specified, they default to 1048576, 8,
       and 1, respectively. The default amount of RAM that may be used by
       scrypt defaults to 1025 MiB.

NOTES
       A context for scrypt can be obtained by calling:

        EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_SCRYPT, NULL);

       The output length of an scrypt key derivation is specified via the
       length parameter to the EVP_PKEY_derive(3) function.

EXAMPLE
       This example derives a 64-byte long test vector using scrypt using the
       password "password", salt "NaCl" and N = 1024, r = 8, p = 16.

        EVP_PKEY_CTX *pctx;
        unsigned char out[64];

        size_t outlen = sizeof(out);
        pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_SCRYPT, NULL);

        if (EVP_PKEY_derive_init(pctx) <= 0) {
            error("EVP_PKEY_derive_init");
        }
        if (EVP_PKEY_CTX_set1_pbe_pass(pctx, "password", 8) <= 0) {
            error("EVP_PKEY_CTX_set1_pbe_pass");
        }
        if (EVP_PKEY_CTX_set1_scrypt_salt(pctx, "NaCl", 4) <= 0) {
            error("EVP_PKEY_CTX_set1_scrypt_salt");
        }
        if (EVP_PKEY_CTX_set_scrypt_N(pctx, 1024) <= 0) {
            error("EVP_PKEY_CTX_set_scrypt_N");
        }
        if (EVP_PKEY_CTX_set_scrypt_r(pctx, 8) <= 0) {
            error("EVP_PKEY_CTX_set_scrypt_r");
        }
        if (EVP_PKEY_CTX_set_scrypt_p(pctx, 16) <= 0) {
            error("EVP_PKEY_CTX_set_scrypt_p");
        }
        if (EVP_PKEY_derive(pctx, out, &outlen) <= 0) {
            error("EVP_PKEY_derive");
        }

        {
            const unsigned char expected[sizeof(out)] = {
                0xfd, 0xba, 0xbe, 0x1c, 0x9d, 0x34, 0x72, 0x00,
                0x78, 0x56, 0xe7, 0x19, 0x0d, 0x01, 0xe9, 0xfe,
                0x7c, 0x6a, 0xd7, 0xcb, 0xc8, 0x23, 0x78, 0x30,
                0xe7, 0x73, 0x76, 0x63, 0x4b, 0x37, 0x31, 0x62,
                0x2e, 0xaf, 0x30, 0xd9, 0x2e, 0x22, 0xa3, 0x88,
                0x6f, 0xf1, 0x09, 0x27, 0x9d, 0x98, 0x30, 0xda,
                0xc7, 0x27, 0xaf, 0xb9, 0x4a, 0x83, 0xee, 0x6d,
                0x83, 0x60, 0xcb, 0xdf, 0xa2, 0xcc, 0x06, 0x40
            };

            assert(!memcmp(out, expected, sizeof(out)));
        }

        EVP_PKEY_CTX_free(pctx);

CONFORMING TO
       RFC 7914

SEE ALSO
       EVP_PKEY_CTX_set1_scrypt_salt(3), EVP_PKEY_CTX_set_scrypt_N(3),
       EVP_PKEY_CTX_set_scrypt_r(3), EVP_PKEY_CTX_set_scrypt_p(3),
       EVP_PKEY_CTX_set_scrypt_maxmem_bytes(3), EVP_PKEY_CTX_new(3),
       EVP_PKEY_CTX_ctrl_str(3), EVP_PKEY_derive(3)

COPYRIGHT
       Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



1.1.1                             2018-09-17                         SCRYPT(7)