NAME

       EVP_KDF-SCRYPT - The scrypt EVP_KDF implementation

DESCRIPTION

       Support for computing the scrypt password-based KDF through the EVP_KDF API.

       The EVP_KDF-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 maximum amount of RAM
       that may be used by scrypt defaults to 1025 MiB.

   Identity
       "SCRYPT" is the name for this implementation; it can be used with the EVP_KDF_fetch()
       function.

   Supported parameters
       The supported parameters are:

       "pass" (OSSL_KDF_PARAM_PASSWORD) <octet string>
       "salt" (OSSL_KDF_PARAM_SALT) <octet string>
           These parameters work as described in "PARAMETERS" in EVP_KDF(3).

       "n" (OSSL_KDF_PARAM_SCRYPT_N) <unsigned integer>
       "r" (OSSL_KDF_PARAM_SCRYPT_R) <unsigned integer>
       "p" (OSSL_KDF_PARAM_SCRYPT_P) <unsigned integer>
       "maxmem_bytes" (OSSL_KDF_PARAM_SCRYPT_MAXMEM) <unsigned integer>
           These parameters configure the scrypt work factors N, r, maxmem and p.  Both N and
           maxmem_bytes are parameters of type uint64_t.  Both r and p are parameters of type
           uint32_t.

       "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
           This can be used to set the property query string when fetching the fixed digest
           internally. NULL is used if this value is not set.

NOTES

       A context for scrypt can be obtained by calling:

        EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SCRYPT", NULL);
        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

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

EXAMPLES

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

        EVP_KDF *kdf;
        EVP_KDF_CTX *kctx;
        unsigned char out[64];
        OSSL_PARAM params[6], *p = params;

        kdf = EVP_KDF_fetch(NULL, "SCRYPT", NULL);
        kctx = EVP_KDF_CTX_new(kdf);
        EVP_KDF_free(kdf);

        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_PASSWORD,
                                                 "password", (size_t)8);
        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                                 "NaCl", (size_t)4);
        *p++ = OSSL_PARAM_construct_uint64(OSSL_KDF_PARAM_SCRYPT_N, (uint64_t)1024);
        *p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_SCRYPT_R, (uint32_t)8);
        *p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_SCRYPT_P, (uint32_t)16);
        *p = OSSL_PARAM_construct_end();
        if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
            error("EVP_KDF_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_KDF_CTX_free(kctx);

CONFORMING TO

       RFC 7914

SEE ALSO

       EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3), EVP_KDF_CTX_set_params(3),
       EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)

COPYRIGHT

       Copyright 2017-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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>.