EVP_KDF-X963.7ossl - Man Page

The X9.63-2001 EVP_KDF implementation


The EVP_KDF-X963 algorithm implements the key derivation function (X963KDF). X963KDF is used by Cryptographic Message Syntax (CMS) for EC KeyAgreement, to derive a key using input such as a shared secret key and shared info.


"X963KDF" is the name for this implementation; it can be used with the EVP_KDF_fetch() function.

Supported parameters

The supported parameters are:

"properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
"digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>

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

"key" (OSSL_KDF_PARAM_KEY) <octet string>

The shared secret used for key derivation. This parameter sets the secret.

"info" (OSSL_KDF_PARAM_INFO) <octet string>

This parameter specifies an optional value for shared info.


X963KDF is very similar to the SSKDF that uses a digest as the auxiliary function, X963KDF appends the counter to the secret, whereas SSKDF prepends the counter.

A context for X963KDF can be obtained by calling:

 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

The output length of an X963KDF is specified via the keylen parameter to the EVP_KDF_derive(3) function.


This example derives 10 bytes, with the secret key "secret" and sharedinfo value "label":

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[4], *p = params;

 kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                         SN_sha256, strlen(SN_sha256));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                          "secret", (size_t)6);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "label", (size_t)5);
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {


Conforming to

"SEC 1: Elliptic Curve Cryptography"

See Also

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


This functionality was added in OpenSSL 3.0.

Referenced By

EVP_KDF-X942-CONCAT.7ossl(7), openssl-kdf.1ossl(1), OSSL_PROVIDER-default.7ossl(7), OSSL_PROVIDER-FIPS.7ossl(7).

2024-02-09 3.2.1 OpenSSL