=pod

=head1 NAME

EVP_KDF-HMAC-DRBG
- The HMAC DRBG DETERMINISTIC EVP_KDF implementation

=head1 DESCRIPTION

Support for a deterministic HMAC DRBG using the B<EVP_KDF> API. This is similar
to L<EVP_RAND-HMAC-DRBG(7)>, but uses fixed values for its entropy and nonce
values. This is used to generate deterministic nonce value required by ECDSA
and DSA (as defined in RFC 6979).

=head2 Identity

"HMAC-DRBG-KDF" 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 "digest" (B<OSSL_DRBG_PARAM_DIGEST>) <UTF8 string>

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

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

=item "entropy" (B<OSSL_KDF_PARAM_HMACDRBG_ENTROPY>) <octet string>

Sets the entropy bytes supplied to the HMAC-DRBG.

=item "nonce" (B<OSSL_KDF_PARAM_HMACDRBG_NONCE>) <octet string>

Sets the nonce bytes supplied to the HMAC-DRBG.

=back

=head1 NOTES

A context for KDF HMAC DRBG can be obtained by calling:

 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "HMAC-DRBG-KDF", NULL);
 EVP_KDF_CTX *kdf_ctx = EVP_KDF_CTX_new(kdf, NULL);

=head1 CONFORMING TO

RFC 6979

=head1 SEE ALSO

L<EVP_KDF(3)>,
L<EVP_KDF(3)/PARAMETERS>

=head1 HISTORY

The EVP_KDF-HMAC-DRBG functionality was added in OpenSSL 3.2.

=head1 COPYRIGHT

Copyright 2022-2023 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