mirror of https://github.com/openssl/openssl.git
159 lines
5.4 KiB
Plaintext
159 lines
5.4 KiB
Plaintext
=pod
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=head1 NAME
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scrypt - EVP_PKEY scrypt KDF support
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=head1 SYNOPSIS
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#include <openssl/kdf.h>
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int EVP_PKEY_CTX_set1_pbe_pass(EVP_PKEY_CTX *pctx, unsigned char *pass,
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int passlen);
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int EVP_PKEY_CTX_set1_scrypt_salt(EVP_PKEY_CTX *pctx, unsigned char *salt,
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int saltlen);
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int EVP_PKEY_CTX_set_scrypt_N(EVP_PKEY_CTX *pctx, uint64_t N);
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int EVP_PKEY_CTX_set_scrypt_r(EVP_PKEY_CTX *pctx, uint64_t r);
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int EVP_PKEY_CTX_set_scrypt_p(EVP_PKEY_CTX *pctx, uint64_t p);
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int EVP_PKEY_CTX_set_scrypt_maxmem_bytes(EVP_PKEY_CTX *pctx, uint64_t maxmem);
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=head1 DESCRIPTION
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The EVP_PKEY_SCRYPT algorithm implements the scrypt password based key
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derivation function, as described in RFC 7914. It is memory-hard in the sense
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that it deliberately requires a significant amount of RAM for efficient
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computation. The intention of this is to render brute forcing of passwords on
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systems that lack large amounts of main memory (such as GPUs or ASICs)
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computationally infeasible.
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scrypt provides three work factors that can be customized: N, r and p. N, which
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has to be a positive power of two, is the general work factor and scales CPU
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time in an approximately linear fashion. r is the block size of the internally
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used hash function and p is the parallelization factor. Both r and p need to be
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greater than zero. The amount of RAM that scrypt requires for its computation
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is roughly (128 * N * r * p) bytes.
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In the original paper of Colin Percival ("Stronger Key Derivation via
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Sequential Memory-Hard Functions", 2009), the suggested values that give a
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computation time of less than 5 seconds on a 2.5 GHz Intel Core 2 Duo are N =
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2^20 = 1048576, r = 8, p = 1. Consequently, the required amount of memory for
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this computation is roughly 1 GiB. On a more recent CPU (Intel i7-5930K at 3.5
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GHz), this computation takes about 3 seconds. When N, r or p are not specified,
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they default to 1048576, 8, and 1, respectively. The default amount of RAM that
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may be used by scrypt defaults to 1025 MiB.
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EVP_PKEY_CTX_set1_pbe_pass() sets the B<passlen> bytes long password.
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EVP_PKEY_CTX_set1_scrypt_salt() sets the B<saltlen> bytes long salt value.
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EVP_PKEY_CTX_set_scrypt_N(), EVP_PKEY_CTX_set_scrypt_r() and
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EVP_PKEY_CTX_set_scrypt_p() configure the work factors N, r and p.
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EVP_PKEY_CTX_set_scrypt_maxmem_bytes() sets how much RAM key derivation may
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maximally use, given in bytes. If RAM is exceeded because the load factors are
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chosen too high, the key derivation will fail.
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=head1 STRING CTRLS
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scrypt also supports string based control operations via
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L<EVP_PKEY_CTX_ctrl_str(3)>.
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The B<password> can be directly specified using the B<type> parameter "pass" or
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given in hex encoding using the "hexpass" parameter. Similarly, the B<salt> can
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either be specified using the B<type> parameter "salt" or in hex encoding by
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using the "hexsalt" parameter. The work factors B<N>, B<r> and B<p> as well as
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B<maxmem_bytes> can be set by using the parameters "N", "r", "p" and
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"maxmem_bytes", respectively.
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=head1 NOTES
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All these functions are implemented as macros.
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A context for scrypt can be obtained by calling:
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EVP_PKEY_CTX *pctx = EVP_PKEY_new_id(EVP_PKEY_SCRYPT, NULL);
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The output length of an scrypt key derivation is specified via the length
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parameter to the L<EVP_PKEY_derive(3)> function.
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=head1 RETURN VALUES
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All these functions return 1 for success and 0 or a negative value for failure.
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In particular a return value of -2 indicates the operation is not supported by
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the public key algorithm.
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=head1 EXAMPLE
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This example derives a 64-byte long test vector using scrypt using the password
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"password", salt "NaCl" and N = 1024, r = 8, p = 16.
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EVP_PKEY_CTX *pctx;
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unsigned char out[64];
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size_t outlen = sizeof(out);
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pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_SCRYPT, NULL);
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if (EVP_PKEY_derive_init(pctx) <= 0) {
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error("EVP_PKEY_derive_init");
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}
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if (EVP_PKEY_CTX_set1_pbe_pass(pctx, "password", 8) <= 0) {
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error("EVP_PKEY_CTX_set1_pbe_pass");
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}
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if (EVP_PKEY_CTX_set1_scrypt_salt(pctx, "NaCl", 4) <= 0) {
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error("EVP_PKEY_CTX_set1_scrypt_salt");
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}
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if (EVP_PKEY_CTX_set_scrypt_N(pctx, 1024) <= 0) {
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error("EVP_PKEY_CTX_set_scrypt_N");
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}
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if (EVP_PKEY_CTX_set_scrypt_r(pctx, 8) <= 0) {
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error("EVP_PKEY_CTX_set_scrypt_r");
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}
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if (EVP_PKEY_CTX_set_scrypt_p(pctx, 16) <= 0) {
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error("EVP_PKEY_CTX_set_scrypt_p");
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}
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if (EVP_PKEY_derive(pctx, out, &outlen) <= 0) {
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error("EVP_PKEY_derive");
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}
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{
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const unsigned char expected[sizeof(out)] = {
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0xfd, 0xba, 0xbe, 0x1c, 0x9d, 0x34, 0x72, 0x00,
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0x78, 0x56, 0xe7, 0x19, 0x0d, 0x01, 0xe9, 0xfe,
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0x7c, 0x6a, 0xd7, 0xcb, 0xc8, 0x23, 0x78, 0x30,
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0xe7, 0x73, 0x76, 0x63, 0x4b, 0x37, 0x31, 0x62,
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0x2e, 0xaf, 0x30, 0xd9, 0x2e, 0x22, 0xa3, 0x88,
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0x6f, 0xf1, 0x09, 0x27, 0x9d, 0x98, 0x30, 0xda,
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0xc7, 0x27, 0xaf, 0xb9, 0x4a, 0x83, 0xee, 0x6d,
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0x83, 0x60, 0xcb, 0xdf, 0xa2, 0xcc, 0x06, 0x40
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};
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assert(!memcmp(out, expected, sizeof(out)));
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}
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EVP_PKEY_CTX_free(pctx);
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=head1 CONFORMING TO
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RFC 7914
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(3)>,
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L<EVP_PKEY_CTX_ctrl_str(3)>,
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L<EVP_PKEY_derive(3)>
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=head1 COPYRIGHT
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Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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