EVP_KDF_KB

Section: OpenSSL (7)
Updated: 2020-07-28
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NAME

EVP_KDF_KB - The Key-Based EVP_KDF implementation

DESCRIPTION

The EVP_KDF_KB algorithm implements the Key-Based key derivation function (KBKDF). KBKDF derives a key from repeated application of a keyed MAC to an input secret (and other optional values).

Numeric identity

EVP_KDF_KB is the numeric identity for this implementation; it can be used with the EVP_KDF_CTX_new_id() function.

Supported controls

The supported controls are:

EVP_KDF_CTRL_SET_KB_MODE

This control expects one argument: "int mode"

Sets the mode for the KBKDF operation. There are two supported modes:

EVP_KDF_KB_MODE_COUNTER: The counter mode of KBKDF should be used. This is the default.
EVP_KDF_KB_MODE_FEEDBACK: The feedback mode of KBKDF should be used.

EVP_KDF_CTRL_SET_KB_MAC_TYPE

This control expects one argument: "int mac_type"

Sets the mac type for the KBKDF operation. There are two supported mac types:

EVP_KDF_KB_MAC_TYPE_HMAC: The HMAC with the digest set by EVP_KDF_CTRL_SET_MD should be used as the mac.
EVP_KDF_KB_MAC_TYPE_CMAC: The CMAC with the cipher set by EVP_KDF_CTRL_SET_CIPHER should be used as the mac.

EVP_KDF_CTRL_SET_MD

EVP_KDF_CTRL_SET_CIPHER

EVP_KDF_CTRL_SET_KEY

EVP_KDF_CTRL_SET_SALT

These controls work as described in ``CONTROLS'' in EVP_KDF_CTX(3).

EVP_KDF_CTRL_SET_KB_INFO

This control expects two arguments: "unsigned char *info", "size_t infolen"

EVP_KDF_CTRL_SET_KB_SEED

This control expects two arguments: "unsigned char *seed", "size_t seedlen"

It is used only in the feedback mode and the length must be the same as the block length of the cipher in CMAC or the size of the digest in HMAC.

The controls EVP_KDF_CTRL_SET_KEY, EVP_KDF_CTRL_SET_SALT, EVP_KDF_CTRL_SET_KB_INFO, and EVP_KDF_CTRL_SET_KB_SEED correspond to KI, Label, Context, and IV (respectively) in SP800-108. As in that document, salt, info, and seed are optional and may be omitted.

Depending on whether mac is CMAC or HMAC, either digest or cipher is required (respectively) and the other is unused.

NOTES

A context for KBKDF can be obtained by calling:

 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_KB);

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

Note that currently OpenSSL only implements counter and feedback modes. Other variants may be supported in the future.

EXAMPLES

This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI ``secret'', Label ``label'', and Context ``context''.

 EVP_KDF_CTX *kctx;
 unsigned char out[10];

 kctx = EVP_KDF_CTX_new_id(EVP_KDF_KB);

 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256());
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_MAC_TYPE, EVP_KDF_KB_MAC_TYPE_HMAC);
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", strlen("secret"));
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "label", strlen("label"));
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_INFO, "context", strlen("context"));
 if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
     error("EVP_KDF_derive");

 EVP_KDF_CTX_free(kctx);

This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI ``secret'', Label ``label'', Context ``context'', and IV ``sixteen bytes iv''.

 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 unsigned char *iv = "sixteen bytes iv";

 kctx = EVP_KDF_CTX_new_id(EVP_KDF_KB);

 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_CIPHER, EVP_aes_256_cbc());
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_MAC_TYPE, EVP_KDF_KB_MAC_TYPE_CMAC);
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_MODE, EVP_KDF_KB_MODE_FEEDBACK);
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", strlen("secret"));
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "label", strlen("label"));
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_INFO, "context", strlen("context"));
 EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KB_SEED, iv, strlen(iv));
 if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
     error("EVP_KDF_derive");

 EVP_KDF_CTX_free(kctx);

CONFORMING TO

NIST SP800-108, IETF RFC 6803, IETF RFC 8009.

HISTORY

This functionality was added to OpenSSL 3.0.

COPYRIGHT

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>.