EVP_KDF-SCRYPT(7SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

💖 EVP_KDF-SCRYPT — the scrypt EVP_KDF implementation 💖

okay bestie, welcome to the EVP_KDF-SCRYPT page from the 7SSL manual — literally the scrypt glow-up, OpenSSL edition ✨

🌸 NAME 🌸

EVP_KDF-SCRYPT — the scrypt EVP_KDF implementation 🎀

🦋 DESCRIPTION 🦋

So basically, this is the support for computing the scrypt password-based KDF through the EVP_KDF API. Slay.

The EVP_KDF-SCRYPT algorithm implements the scrypt password-based key derivation function, exactly as described in RFC 7914. It's memory-hard, meaning it deliberately eats a whole lot of RAM to do its thing efficiently. Why? Because the whole point is to make brute forcing passwords on machines that don't have tons of main memory — think GPUs or ASICs — computationally infeasible. not them being humbled by RAM requirements 💀

scrypt gives you three work factors you can customize: N, r and p.

  • N — has to be a positive power of two. This is the general work factor, and it scales CPU time in an approximately linear fashion.
  • r — the block size of the internally used hash function.
  • p — the parallelization factor.

Both r and p need to be greater than zero, no exceptions bestie. The amount of RAM scrypt needs for its computation is roughly (128 * N * r * p) bytes. math ate fr 🧮

In the original paper by 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. So 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 maximum amount of RAM that may be used by scrypt defaults to 1025 MiB. defaults really said "i got you" 🫶

🎀 Identity 🎀

"SCRYPT" is the name for this implementation — that's its whole identity, its main character energy 👑. It can be used with the EVP_KDF_fetch() function.

✨ Supported parameters ✨

The supported parameters are, in order, no skipping:

  • "pass" (OSSL_KDF_PARAM_PASSWORD) <octet string>
  • "salt" (OSSL_KDF_PARAM_SALT) <octet string>

These parameters work as described in "PARAMETERS" in EVP_KDF(3). iykyk 💅

  • "n" (OSSL_KDF_PARAM_SCRYPT_N) <unsigned integer>
  • "r" (OSSL_KDF_PARAM_SCRYPT_R) <unsigned integer>
  • "p" (OSSL_KDF_PARAM_SCRYPT_P) <unsigned integer>
  • "maxmem_bytes" (OSSL_KDF_PARAM_SCRYPT_MAXMEM) <unsigned integer>

These parameters configure the scrypt work factors N, r, maxmem and p. Both N and maxmem_bytes are parameters of type uint64_t. Both r and p are parameters of type uint32_t.

  • "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>

This can be used to set the property query string when fetching the fixed digest internally. NULL is used if this value is not set.

💜 NOTES 💜

A context for scrypt can be obtained by calling:

EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SCRYPT", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

The output length of an scrypt key derivation is specified via the "keylen" parameter to the EVP_KDF_derive(3) function. 📏

🌈 EXAMPLES 🌈

This example derives a 64-byte long test vector using scrypt with the password "password", salt "NaCl" and N = 1024, r = 8, p = 16. watch it cook 🔥

EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[64];
OSSL_PARAM params[6], *p = params;

kdf = EVP_KDF_fetch(NULL, "SCRYPT", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);

*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_PASSWORD,
                                         "password", (size_t)8);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                         "NaCl", (size_t)4);
*p++ = OSSL_PARAM_construct_uint64(OSSL_KDF_PARAM_SCRYPT_N, (uint64_t)1024);
*p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_SCRYPT_R, (uint32_t)8);
*p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_SCRYPT_P, (uint32_t)16);
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
    error("EVP_KDF_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_KDF_CTX_free(kctx);

⭐ CONFORMING TO ⭐

RFC 7914 — certified, official, periodt 💅

🌸 SEE ALSO 🌸

go read those, bestie, they're the supporting cast 🫶

🦋 HISTORY 🦋

This functionality was added in OpenSSL 3.0. so it's not even that old, it's giving fresh 👑

Copyright 2017-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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>.

legal girlies, read the license fr — do not just vibe past it 💀

and that's the whole page bestie!! this one's from OpenSSL 4.0.3, dated 2026-09-29 — love that for us, mwah, go derive some keys responsibly 💅✨🎀

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