[thirdparty/openssl.git] / doc / man7 / EVP_KDF-KRB5KDF.pod

=pod

=head1 NAME

EVP_KDF-KRB5KDF - The RFC3961 Krb5 KDF EVP_KDF implementation

=head1 DESCRIPTION

Support for computing the B<KRB5KDF> KDF through the B<EVP_KDF> API.

The EVP_KDF-KRB5KDF algorithm implements the key derivation function defined
in RFC 3961, section 5.1 and is used by Krb5 to derive session keys.
Three inputs are required to perform key derivation: a cipher, (for example
AES-128-CBC), the initial key, and a constant.

=head2 Identity

"KRB5KDF" is the name for this implementation;
it can be used with the EVP_KDF_fetch() function.

=head2 Supported parameters

The supported parameters are:

=over 4

=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>

=item "cipher" (B<OSSL_KDF_PARAM_CIPHER>) <UTF8 string>

=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>

These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.

=item "constant" (B<OSSL_KDF_PARAM_CONSTANT>) <octet string>

This parameter sets the constant value for the KDF.
If a value is already set, the contents are replaced.

=back

=head1 NOTES

A context for KRB5KDF can be obtained by calling:

 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
 EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

The output length of the KRB5KDF derivation is specified via the I<keylen>
parameter to the L<EVP_KDF_derive(3)> function, and MUST match the key
length for the chosen cipher or an error is returned. Moreover, the
constant's length must not exceed the block size of the cipher.
Since the KRB5KDF output length depends on the chosen cipher, calling
L<EVP_KDF_CTX_get_kdf_size(3)> to obtain the requisite length returns the correct length
only after the cipher is set. Prior to that B<EVP_MAX_KEY_LENGTH> is returned.
The caller must allocate a buffer of the correct length for the chosen
cipher, and pass that buffer to the L<EVP_KDF_derive(3)> function along
with that length.

=head1 EXAMPLES

This example derives a key using the AES-128-CBC cipher:

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char key[16] = "01234...";
 unsigned char constant[] = "I'm a constant";
 unsigned char out[16];
 size_t outlen = sizeof(out);
 OSSL_PARAM params[4], *p = params;

 kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER,
                                         SN_aes_128_cbc,
                                         strlen(SN_aes_128_cbc));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          key, (size_t)16);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_CONSTANT,
                                          constant, strlen(constant));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_derive(kctx, out, outlen, params) <= 0)
     /* Error */

 EVP_KDF_CTX_free(kctx);

=head1 CONFORMING TO

RFC 3961

=head1 SEE ALSO

L<EVP_KDF(3)>,
L<EVP_KDF_CTX_free(3)>,
L<EVP_KDF_CTX_get_kdf_size(3)>,
L<EVP_KDF_derive(3)>,
L<EVP_KDF(3)/PARAMETERS>

=head1 HISTORY

This functionality was added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2016-2021 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
L<https://www.openssl.org/source/license.html>.

=cut
Commit	Line	Data
33f54da3 SS	1	=pod
	2
	3	=head1 NAME
	4
	5	EVP_KDF-KRB5KDF - The RFC3961 Krb5 KDF EVP_KDF implementation
	6
	7	=head1 DESCRIPTION
	8
	9	Support for computing the B<KRB5KDF> KDF through the B<EVP_KDF> API.
	10
	11	The EVP_KDF-KRB5KDF algorithm implements the key derivation function defined
	12	in RFC 3961, section 5.1 and is used by Krb5 to derive session keys.
	13	Three inputs are required to perform key derivation: a cipher, (for example
	14	AES-128-CBC), the initial key, and a constant.
	15
	16	=head2 Identity
	17
	18	"KRB5KDF" is the name for this implementation;
	19	it can be used with the EVP_KDF_fetch() function.
	20
	21	=head2 Supported parameters
	22
	23	The supported parameters are:
	24
	25	=over 4
	26
a90311fe	27	=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
33f54da3 SS	28
	29	=item "cipher" (B<OSSL_KDF_PARAM_CIPHER>) <UTF8 string>
	30
	31	=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
	32
	33	These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
	34
	35	=item "constant" (B<OSSL_KDF_PARAM_CONSTANT>) <octet string>
	36
	37	This parameter sets the constant value for the KDF.
	38	If a value is already set, the contents are replaced.
	39
	40	=back
	41
	42	=head1 NOTES
	43
	44	A context for KRB5KDF can be obtained by calling:
	45
	46	EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
660c5344	47	EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
33f54da3 SS	48
	49	The output length of the KRB5KDF derivation is specified via the I<keylen>
	50	parameter to the L<EVP_KDF_derive(3)> function, and MUST match the key
8c1cbc72	51	length for the chosen cipher or an error is returned. Moreover, the
33f54da3 SS	52	constant's length must not exceed the block size of the cipher.
33f54da3 SS	53	Since the KRB5KDF output length depends on the chosen cipher, calling
1ba21239	54	L<EVP_KDF_CTX_get_kdf_size(3)> to obtain the requisite length returns the correct length
33f54da3 SS	55	only after the cipher is set. Prior to that B<EVP_MAX_KEY_LENGTH> is returned.
	56	The caller must allocate a buffer of the correct length for the chosen
	57	cipher, and pass that buffer to the L<EVP_KDF_derive(3)> function along
	58	with that length.
	59
	60	=head1 EXAMPLES
	61
	62	This example derives a key using the AES-128-CBC cipher:
	63
	64	EVP_KDF *kdf;
	65	EVP_KDF_CTX *kctx;
	66	unsigned char key[16] = "01234...";
	67	unsigned char constant[] = "I'm a constant";
	68	unsigned char out[16];
	69	size_t outlen = sizeof(out);
	70	OSSL_PARAM params[4], *p = params;
	71
	72	kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL);
660c5344	73	kctx = EVP_KDF_CTX_new(kdf);
33f54da3 SS	74	EVP_KDF_free(kdf);
	75
	76	*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER,
	77	SN_aes_128_cbc,
	78	strlen(SN_aes_128_cbc));
	79	*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
	80	key, (size_t)16);
	81	*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_CONSTANT,
	82	constant, strlen(constant));
	83	*p = OSSL_PARAM_construct_end();
6980e36a	84	if (EVP_KDF_derive(kctx, out, outlen, params) <= 0)
33f54da3 SS	85	/* Error */
33f54da3 SS	86
660c5344	87	EVP_KDF_CTX_free(kctx);
33f54da3 SS	88
	89	=head1 CONFORMING TO
	90
	91	RFC 3961
	92
	93	=head1 SEE ALSO
	94
6e4618a0	95	L<EVP_KDF(3)>,
660c5344	96	L<EVP_KDF_CTX_free(3)>,
1ba21239	97	L<EVP_KDF_CTX_get_kdf_size(3)>,
33f54da3 SS	98	L<EVP_KDF_derive(3)>,
	99	L<EVP_KDF(3)/PARAMETERS>
	100
	101	=head1 HISTORY
	102
4741c80c	103	This functionality was added in OpenSSL 3.0.
33f54da3 SS	104
	105	=head1 COPYRIGHT
	106
8020d79b	107	Copyright 2016-2021 The OpenSSL Project Authors. All Rights Reserved.
33f54da3	108
a6ed19dc	109	Licensed under the Apache License 2.0 (the "License"). You may not use
33f54da3 SS	110	this file except in compliance with the License. You can obtain a copy
	111	in the file LICENSE in the source distribution or at
	112	L<https://www.openssl.org/source/license.html>.
	113
	114	=cut
	115