SCRYPT(7) | OpenSSL | SCRYPT(7) |

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.

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.

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);

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>.

2022-03-15 | 1.1.1n |