5 EVP_KDF_SCRYPT - The scrypt EVP_KDF implementation
9 Support for computing the B<scrypt> password-based KDF through the B<EVP_KDF>
12 The EVP_KDF_SCRYPT algorithm implements the scrypt password-based key
13 derivation function, as described in RFC 7914. It is memory-hard in the sense
14 that it deliberately requires a significant amount of RAM for efficient
15 computation. The intention of this is to render brute forcing of passwords on
16 systems that lack large amounts of main memory (such as GPUs or ASICs)
17 computationally infeasible.
19 scrypt provides three work factors that can be customized: N, r and p. N, which
20 has to be a positive power of two, is the general work factor and scales CPU
21 time in an approximately linear fashion. r is the block size of the internally
22 used hash function and p is the parallelization factor. Both r and p need to be
23 greater than zero. The amount of RAM that scrypt requires for its computation
24 is roughly (128 * N * r * p) bytes.
26 In the original paper of Colin Percival ("Stronger Key Derivation via
27 Sequential Memory-Hard Functions", 2009), the suggested values that give a
28 computation time of less than 5 seconds on a 2.5 GHz Intel Core 2 Duo are N =
29 2^20 = 1048576, r = 8, p = 1. Consequently, the required amount of memory for
30 this computation is roughly 1 GiB. On a more recent CPU (Intel i7-5930K at 3.5
31 GHz), this computation takes about 3 seconds. When N, r or p are not specified,
32 they default to 1048576, 8, and 1, respectively. The maximum amount of RAM that
33 may be used by scrypt defaults to 1025 MiB.
35 =head2 Numeric identity
37 B<EVP_KDF_SCRYPT> is the numeric identity for this implementation; it
38 can be used with the EVP_KDF_CTX_new_id() function.
40 =head2 Supported controls
42 The supported controls are:
46 =item B<EVP_KDF_CTRL_SET_PASS>
48 =item B<EVP_KDF_CTRL_SET_SALT>
50 These controls work as described in L<EVP_KDF_CTX(3)/CONTROLS>.
52 =item B<EVP_KDF_CTRL_SET_SCRYPT_N>
54 =item B<EVP_KDF_CTRL_SET_SCRYPT_R>
56 =item B<EVP_KDF_CTRL_SET_SCRYPT_P>
58 B<EVP_KDF_CTRL_SET_SCRYPT_N> expects one argument: C<uint64_t N>
60 B<EVP_KDF_CTRL_SET_SCRYPT_R> expects one argument: C<uint32_t r>
62 B<EVP_KDF_CTRL_SET_SCRYPT_P> expects one argument: C<uint32_t p>
64 These controls configure the scrypt work factors N, r and p.
66 EVP_KDF_ctrl_str() type strings: "N", "r" and "p", respectively.
68 The corresponding value strings are expected to be decimal numbers.
74 A context for scrypt can be obtained by calling:
76 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SCRYPT);
78 The output length of an scrypt key derivation is specified via the
79 B<keylen> parameter to the L<EVP_KDF_derive(3)> function.
83 This example derives a 64-byte long test vector using scrypt with the password
84 "password", salt "NaCl" and N = 1024, r = 8, p = 16.
87 unsigned char out[64];
89 kctx = EVP_KDF_CTX_new_id(EVP_KDF_SCRYPT);
91 if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_PASS, "password", (size_t)8) <= 0) {
92 error("EVP_KDF_CTRL_SET_PASS");
94 if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "NaCl", (size_t)4) <= 0) {
95 error("EVP_KDF_CTRL_SET_SALT");
97 if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SCRYPT_N, (uint64_t)1024) <= 0) {
98 error("EVP_KDF_CTRL_SET_SCRYPT_N");
100 if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SCRYPT_R, (uint32_t)8) <= 0) {
101 error("EVP_KDF_CTRL_SET_SCRYPT_R");
103 if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SCRYPT_P, (uint32_t)16) <= 0) {
104 error("EVP_KDF_CTRL_SET_SCRYPT_P");
106 if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
107 error("EVP_KDF_derive");
111 const unsigned char expected[sizeof(out)] = {
112 0xfd, 0xba, 0xbe, 0x1c, 0x9d, 0x34, 0x72, 0x00,
113 0x78, 0x56, 0xe7, 0x19, 0x0d, 0x01, 0xe9, 0xfe,
114 0x7c, 0x6a, 0xd7, 0xcb, 0xc8, 0x23, 0x78, 0x30,
115 0xe7, 0x73, 0x76, 0x63, 0x4b, 0x37, 0x31, 0x62,
116 0x2e, 0xaf, 0x30, 0xd9, 0x2e, 0x22, 0xa3, 0x88,
117 0x6f, 0xf1, 0x09, 0x27, 0x9d, 0x98, 0x30, 0xda,
118 0xc7, 0x27, 0xaf, 0xb9, 0x4a, 0x83, 0xee, 0x6d,
119 0x83, 0x60, 0xcb, 0xdf, 0xa2, 0xcc, 0x06, 0x40
122 assert(!memcmp(out, expected, sizeof(out)));
125 EVP_KDF_CTX_free(kctx);
134 L<EVP_KDF_CTX_new_id(3)>,
135 L<EVP_KDF_CTX_free(3)>,
137 L<EVP_KDF_derive(3)>,
138 L<EVP_KDF_CTX(3)/CONTROLS>
142 Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
144 Licensed under the Apache License 2.0 (the "License"). You may not use
145 this file except in compliance with the License. You can obtain a copy
146 in the file LICENSE in the source distribution or at
147 L<https://www.openssl.org/source/license.html>.