SCRYPT(7SSL) OpenSSL SCRYPT(7SSL)
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.
EXAMPLES
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 2017-2019 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>.
1.1.1g 2020-04-21 SCRYPT(7SSL)