=pod

=head1 NAME

PKCS5_PBKDF2_HMAC, PKCS5_PBKDF2_HMAC_SHA1 - password based derivation routines with salt and iteration count

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int PKCS5_PBKDF2_HMAC(const char *pass, int passlen,
                       const unsigned char *salt, int saltlen, int iter,
                       const EVP_MD *digest,
                       int keylen, unsigned char *out);

int PKCS5_PBKDF2_HMAC_SHA1(const char *pass, int passlen,
			   const unsigned char *salt, int saltlen, int iter,
			   int keylen, unsigned char *out);

=head1 DESCRIPTION

PKCS5_PBKDF2_HMAC() derives a key from a password using a salt and iteration count
as specified in RFC 2898.

B<pass> is the password used in the derivation of length B<passlen>. B<pass>
is an optional parameter and can be NULL. If B<passlen> is -1, then the
function will calculate the length of B<pass> using strlen().

B<salt> is the salt used in the derivation of length B<saltlen>. If the
B<salt> is NULL, then B<saltlen> must be 0. The function will not
attempt to calculate the length of the B<salt> because it is not assumed to
be NULL terminated.

B<iter> is the iteration count and its value should be greater than or 
equal to 1. RFC 2898 suggests an iteration count of at least 1000. Any
B<iter> less than 1 is treated as a single iteration.

B<digest> is the message digest function used in the derivation. Values include
any of the EVP_* message digests. PKCS5_PBKDF2_HMAC_SHA1() calls
PKCS5_PBKDF2_HMAC() with EVP_sha1().

The derived key will be written to B<out>. The size of the B<out> buffer
is specified via B<keylen>.

=head1 NOTES

A typical application of this function is to derive keying material for an
encryption algorithm from a password in the B<pass>, a salt in B<salt>,
and an iteration count.

Increasing the B<iter> parameter slows down the algorithm which makes it
harder for an attacker to peform a brute force attack using a large number
of candidate passwords.

=head1 RETURN VALUES

PKCS5_PBKDF2_HMAC() and PBKCS5_PBKDF2_HMAC_SHA1() return 1 on success or 0 on error.

=head1 SEE ALSO

L<evp(3)|evp(3)>, L<rand(3)|rand(3)>,
L<EVP_BytesToKey(3)|EVP_BytesToKey(3)>

=head1 HISTORY

=cut
