EVP_KDF-X942-ASN1(7ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

🌸 NAME 🌸

okay so bestie, this page is EVP_KDF-X942-ASN1(7ossl) from OpenSSL, and it’s the manual for EVP_KDF-X942-ASN1 — the X9.42-2003 asn1 EVP_KDF implementation. No cap. 💖

💖 DESCRIPTION 💖

The EVP_KDF-X942-ASN1 algorithm implements the key derivation function X942KDF-ASN1. It’s used by DH KeyAgreement to derive a key using input such as a shared secret key and other info. The other info is DER encoded data that contains a 32 bit counter as well as optional fields for "partyu-info", "partyv-info", "supp-pubinfo" and "supp-privinfo". This kdf is used by Cryptographic Message Syntax (CMS). ✨

The output is considered to be keying material. Periodt. 💅

🪞 Identity 🪞

"X942KDF-ASN1" or "X942KDF" is the name for this implementation; it can be used with the EVP_KDF_fetch() function. Slay. 🎀

✨ Supported parameters ✨

Here’s the parameter menu, bestie — names, macros, and types stay exactly as they are. 🫶

  • "properties" (OSSL_KDF_PARAM_PROPERTIES) — type: `<UTF8 string>`. Works as described in “PARAMETERS” in EVP_KDF(3).
  • "digest" (OSSL_KDF_PARAM_DIGEST) — type: `<UTF8 string>`. Works as described in “PARAMETERS” in EVP_KDF(3).
  • "secret" (OSSL_KDF_PARAM_SECRET) — type: `<octet string>`. The shared secret used for key derivation. This parameter sets the secret. 💜
  • "acvp-info" (OSSL_KDF_PARAM_X942_ACVPINFO) — type: `<octet string>`. This value should not be used in production and should only be used for ACVP testing. It is an optional octet string containing a combined DER encoded blob of any of the optional fields related to "partyu-info", "partyv-info", "supp-pubinfo" and "supp-privinfo". If it is specified then none of these other fields should be used. 🚨
  • "partyu-info" (OSSL_KDF_PARAM_X942_PARTYUINFO) — type: `<octet string>`. An optional octet string containing public info contributed by the initiator. 🌸
  • "ukm" (OSSL_KDF_PARAM_UKM) — type: `<octet string>`. An alias for "partyu-info". In CMS this is the user keying material. 🦋
  • "partyv-info" (OSSL_KDF_PARAM_X942_PARTYVINFO) — type: `<octet string>`. An optional octet string containing public info contributed by the responder. 💖
  • "supp-pubinfo" (OSSL_KDF_PARAM_X942_SUPP_PUBINFO) — type: `<octet string>`. An optional octet string containing some additional, mutually-known public information. Setting this value also sets "use-keybits" to 0. ✨
  • "use-keybits" (OSSL_KDF_PARAM_X942_USE_KEYBITS) — type: `<integer>`. The default value of 1 will use the KEK key length (in bits) as the "supp-pubinfo". A value of 0 disables setting the "supp-pubinfo". 🔥
  • "supp-privinfo" (OSSL_KDF_PARAM_X942_SUPP_PRIVINFO) — type: `<octet string>`. An optional octet string containing some additional, mutually-known private information. 🙈
  • "cekalg" (OSSL_KDF_PARAM_CEK_ALG) — type: `<UTF8 string>`. This parameter sets the CEK wrapping algorithm name. Valid values are "AES-128-WRAP", "AES-192-WRAP", "AES-256-WRAP" and "DES3-WRAP". 👑

The OpenSSL FIPS provider also supports the following parameters: 🔐

  • "fips-indicator" (OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR) — type: `<integer>`. A getter that returns 1 if the operation is FIPS approved, or 0 otherwise. This may be used after calling EVP_KDF_derive. It returns 0 if "key-check" parameter is set to 0 and the check fails.
  • "key-check" (OSSL_KDF_PARAM_FIPS_KEY_CHECK) — type: `<integer>`. The default value of 1 causes an error during EVP_KDF_CTX_set_params() if the length of used key-derivation key (OSSL_KDF_PARAM_KEY) is shorter than 112 bits. Setting this to zero will ignore the error and set the approved "fips-indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0. 💀

📝 NOTES 📝

A context for X942KDF can be obtained by calling:

        EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

The output length of an X942KDF is specified via the keylen parameter to the EVP_KDF_derive(3) function. 🌈

🍓 EXAMPLES 🍓

Okay so this example derives 24 bytes, with the secret key "secret" and random user keying material:

         EVP_KDF_CTX *kctx;
         EVP_KDF_CTX *kctx;
         unsigned char out[192/8];
         unsignred char ukm[64];
         OSSL_PARAM params[5], *p = params;

         if (RAND_bytes(ukm, sizeof(ukm)) <= 0)
             error("RAND_bytes");

         kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
         if (kctx == NULL)
             error("EVP_KDF_fetch");
         kctx = EVP_KDF_CTX_new(kdf);
         EVP_KDF_free(kdf);
         if (kctx == NULL)
             error("EVP_KDF_CTX_new");

         *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, "SHA256", 0);
         *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                                  "secret", (size_t)6);
         *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_UKM, ukm, sizeof(ukm));
         *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CEK_ALG, "AES-256-WRAP, 0);
         *p = OSSL_PARAM_construct_end();
         if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0)
             error("EVP_KDF_derive");

         EVP_KDF_CTX_free(kctx);

🌈 CONFORMING TO 🌈

ANS1 X9.42-2003 RFC 2631 — yes bestie, that’s the exact spelling from the original, and I’m not touching it. 💫

👀 SEE ALSO 👀

🦋 HISTORY 🦋

This functionality was added in OpenSSL 3.0. Iconic behavior. 👑

Copyright 2019-2021 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>. 🫶

bye bestie 💅 — this one is from OpenSSL 3.5.9, dated 2026-09-29, and it lives under the manual name EVP_KDF-X942-ASN1(7ossl). ✨🎀

📦 where this page comes from