forked from cory/tildefriends
Cory McWilliams
09ddfffa6b
git-svn-id: https://www.unprompted.com/svn/projects/tildefriends/trunk@4088 ed5197a5-7fde-0310-b194-c3ffbd925b24
249 lines
8.1 KiB
Groff
249 lines
8.1 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "SCRYPT 7"
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.TH SCRYPT 7 "2020-04-21" "1.1.1g" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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scrypt \- EVP_PKEY scrypt KDF support
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \s-1EVP_PKEY_SCRYPT\s0 algorithm implements the scrypt password based key
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derivation function, as described in \s-1RFC 7914.\s0 It is memory-hard in the sense
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that it deliberately requires a significant amount of \s-1RAM\s0 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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.PP
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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 \s-1CPU\s0
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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 \s-1RAM\s0 that scrypt requires for its computation
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is roughly (128 * N * r * p) bytes.
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.PP
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In the original paper of Colin Percival (\*(L"Stronger Key Derivation via
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Sequential Memory-Hard Functions\*(R", 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 \s-1CPU\s0 (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 \s-1RAM\s0 that
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may be used by scrypt defaults to 1025 MiB.
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.SH "NOTES"
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.IX Header "NOTES"
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A context for scrypt can be obtained by calling:
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.PP
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.Vb 1
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\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_SCRYPT, NULL);
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.Ve
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.PP
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The output length of an scrypt key derivation is specified via the
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length parameter to the \fBEVP_PKEY_derive\fR\|(3) function.
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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This example derives a 64\-byte long test vector using scrypt using the password
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\&\*(L"password\*(R", salt \*(L"NaCl\*(R" and N = 1024, r = 8, p = 16.
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.PP
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.Vb 2
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\& EVP_PKEY_CTX *pctx;
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\& unsigned char out[64];
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\&
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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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\&
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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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\& {
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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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\&
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\& assert(!memcmp(out, expected, sizeof(out)));
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\& }
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\&
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\& EVP_PKEY_CTX_free(pctx);
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.Ve
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.SH "CONFORMING TO"
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.IX Header "CONFORMING TO"
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\&\s-1RFC 7914\s0
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fBEVP_PKEY_CTX_set1_scrypt_salt\fR\|(3),
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\&\fBEVP_PKEY_CTX_set_scrypt_N\fR\|(3),
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\&\fBEVP_PKEY_CTX_set_scrypt_r\fR\|(3),
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\&\fBEVP_PKEY_CTX_set_scrypt_p\fR\|(3),
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\&\fBEVP_PKEY_CTX_set_scrypt_maxmem_bytes\fR\|(3),
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\&\fBEVP_PKEY_CTX_new\fR\|(3),
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\&\fBEVP_PKEY_CTX_ctrl_str\fR\|(3),
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\&\fBEVP_PKEY_derive\fR\|(3)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2017\-2019 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the OpenSSL license (the \*(L"License\*(R"). 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 \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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