EVP_KDF_KB(7)

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.

SEE ALSO
EVP_KDF_CTX(3), EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3), EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), "CONTROLS" in EVP_KDF_CTX(3)

HISTORY
This functionality was added to OpenSSL 3.0.

COPYRIGHT
Copyright 2019 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red Hat, Inc.

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>.