EVP_KDF-ARGON2(7ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

💜 EVP_KDF-ARGON2 — the Argon2 EVP KDF implementation

okay so bestie, this one is from the OpenSSL fam (manual page EVP_KDF-ARGON2(7ossl), in case you were wondering) and it's all about computing the argon2 password-based KDF through the EVP_KDF API. yes that's the whole vibe. let's get into it ✨

🌸 DESCRIPTION 🌸

So this page is all about computing the argon2 password-based KDF through the EVP_KDF API. that's the whole point of it existing 💅

The EVP_KDF-ARGON2 algorithm implements the Argon2 password-based key derivation function, exactly as described in IETF RFC 9106. It's memory-hard — and like, not in a cute way, in a "it deliberately requires a significant amount of RAM for efficient computation" way. The whole intention here is to render brute forcing of passwords on systems that lack large amounts of main memory (such as GPUs or ASICs) computationally infeasible. so it just absolutely eats RAM on purpose to make the bad guys' lives miserable. iconic behavior honestly 🔥

Argon2d (Argon2i) uses data-dependent (data-independent) memory access and primary seek to address trade-off (side-channel) attacks.

Argon2id is a hybrid construction which — and this is the part you actually need to remember — in the first two slices of the first pass, generates reference addresses data-independently as in Argon2i, whereas in later slices and next passes it generates them data-dependently as in Argon2d. yes it's literally doing both. main character energy 🎀

Sbox-hardened version Argon2ds is not supported. like nope, not happening, don't ask 🙈

For more information, please refer to RFC 9106.

🦋 Supported parameters 🦋

The supported parameters are:

  • "pass" (OSSL_KDF_PARAM_PASSWORD) <octet string>
  • "salt" (OSSL_KDF_PARAM_SALT) <octet string>
  • "secret" (OSSL_KDF_PARAM_SECRET) <octet string>
  • "iter" (OSSL_KDF_PARAM_ITER) <unsigned integer>
  • "size" (OSSL_KDF_PARAM_SIZE) <unsigned integer>
  • "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>

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

🫶 Note that RFC 9106 recommends 128 bits salt for most applications, or 64 bits salt in the case of space constraints. At least 128 bits output length is recommended. (yes, there's a minimum, please respect it 💜)

Note that secret (or pepper) is an optional secret data used along the password. spicy optional extra, we love her 🌶️

  • "threads" (OSSL_KDF_PARAM_THREADS) <unsigned integer> — the number of threads, bounded above by the number of lanes.

This can only be used with built-in thread support. Threading must be explicitly enabled. See EXAMPLES section for more information.

  • "ad" (OSSL_KDF_PARAM_ARGON2_AD) <octet string> — optional associated data, may be used to "tag" a group of keys, or tie them to a particular public key, without having to modify salt. cute little label system, no salt editing required 💅
  • "lanes" (OSSL_KDF_PARAM_ARGON2_LANES) <unsigned integer> — Argon2 splits the requested memory size into lanes, each of which is designed to be processed in parallel. For example, on a system with p cores, it's recommended to use p lanes.

The number of lanes is used to derive the key. It is possible to specify more lanes than the number of available computational threads. This is especially encouraged if multi-threading is disabled.

  • "memcost" (OSSL_KDF_PARAM_ARGON2_MEMCOST) <unsigned integer> — memory cost parameter (the number of 1k memory blocks used). this is the one that makes GPUs cry 😭
  • "version" (OSSL_KDF_PARAM_ARGON2_VERSION) <unsigned integer> — Argon2 version. Supported values: 0x10, 0x13 (default). so 0x13 is the vibe unless you say otherwise ⭐
  • "early_clean" (OSSL_KDF_PARAM_EARLY_CLEAN) <unsigned integer> — if set (nonzero), password and secret stored in Argon2 context are zeroed early during initial hash computation, as soon as they are not needed. Otherwise, they are zeroed along the rest of Argon2 context data on clear, free, reset.

This can be useful if, for example, multiple keys with different ad value are to be generated from a single password and secret. so like, keep the password around, wipe the risky bits early. big brain move 🧠✨

🌈 EXAMPLES 🌈

This example uses Argon2d with password "1234567890", salt "saltsalt", using 2 lanes, 2 threads, and memory cost of 65536:

#include <string.h>                 /* strlen               */
#include <openssl/core_names.h>     /* OSSL_KDF_*           */
#include <openssl/params.h>         /* OSSL_PARAM_*         */
#include <openssl/thread.h>         /* OSSL_set_max_threads */
#include <openssl/kdf.h>            /* EVP_KDF_*            */

int main(void)
{
    int retval = 1;

    EVP_KDF *kdf = NULL;
    EVP_KDF_CTX *kctx = NULL;
    OSSL_PARAM params[6], *p = params;

    /* argon2 params, please refer to RFC9106 for recommended defaults */
    uint32_t lanes = 2, threads = 2, memcost = 65536;
    char pwd[] = "1234567890", salt[] = "saltsalt";

    /* derive result */
    size_t outlen = 128;
    unsigned char result[outlen];

    /* required if threads > 1 */
    if (OSSL_set_max_threads(NULL, threads) != 1)
        goto fail;

    p = params;
    *p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_THREADS, &threads);
    *p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_ARGON2_LANES,
                                       &lanes);
    *p++ = OSSL_PARAM_construct_uint32(OSSL_KDF_PARAM_ARGON2_MEMCOST,
                                       &memcost);
    *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                             salt,
                                             strlen((const char *)salt));
    *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_PASSWORD,
                                             pwd,
                                             strlen((const char *)pwd));
    *p++ = OSSL_PARAM_construct_end();

    if ((kdf = EVP_KDF_fetch(NULL, "ARGON2D", NULL)) == NULL)
        goto fail;
    if ((kctx = EVP_KDF_CTX_new(kdf)) == NULL)
        goto fail;
    if (EVP_KDF_derive(kctx, &result[0], outlen, params) != 1)
        goto fail;

    printf("Output = %s\n", OPENSSL_buf2hexstr(result, outlen));
    retval = 0;

fail:
    EVP_KDF_free(kdf);
    EVP_KDF_CTX_free(kctx);
    OSSL_set_max_threads(NULL, 0);

    return retval;
}
🫶 bestie note: that OSSL_set_max_threads(NULL, threads) bit is required if threads > 1 — it's right there in the comment, don't skip it, and don't forget to reset it with OSSL_set_max_threads(NULL, 0) when you're done. clean up after yourself, periodt 💅

🌟 NOTES 🌟

"ARGON2I", "ARGON2D", and "ARGON2ID" are the names for this implementation; it can be used with the EVP_KDF_fetch() function. three names, one algorithm, pick your fighter 👑

👑 CONFORMING TO 👑

RFC 9106 Argon2, see <https://www.rfc-editor.org/rfc/rfc9106.txt>. go read it, iykyk 📖

💖 SEE ALSO 💖

EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3), EVP_KDF_CTX_set_params(3), EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)

⭐ HISTORY ⭐

This functionality was added to OpenSSL 3.2. so if you're on something older, that's why it's giving "command not found" energy 💀

Copyright 2022-2024 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>.

okay that's the whole page bestie, go forth and argon2 responsibly 💜✨

mwah 💋 this was OpenSSL 3.5.6, dated 2026-04-07 — see you in the next man page, love u, bye 🫶

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