68 lines
2.1 KiB
Text
68 lines
2.1 KiB
Text
|
=pod
|
||
|
|
|
||
|
|
=head1 NAME
|
||
|
|
|
||
|
|
EVP_BytesToKey - password based encryption routine
|
||
|
|
|
||
|
|
=head1 SYNOPSIS
|
||
|
|
|
||
|
|
#include <openssl/evp.h>
|
||
|
|
|
||
|
|
int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md,
|
||
|
|
const unsigned char *salt,
|
||
|
|
const unsigned char *data, int datal, int count,
|
||
|
|
unsigned char *key,unsigned char *iv);
|
||
|
|
|
||
|
|
=head1 DESCRIPTION
|
||
|
|
|
||
|
|
EVP_BytesToKey() derives a key and IV from various parameters. B<type> is
|
||
|
|
the cipher to derive the key and IV for. B<md> is the message digest to use.
|
||
|
|
The B<salt> paramter is used as a salt in the derivation: it should point to
|
||
|
|
an 8 byte buffer or NULL if no salt is used. B<data> is a buffer containing
|
||
|
|
B<datal> bytes which is used to derive the keying data. B<count> is the
|
||
|
|
iteration count to use. The derived key and IV will be written to B<key>
|
||
|
|
and B<iv> respectively.
|
||
|
|
|
||
|
|
=head1 NOTES
|
||
|
|
|
||
|
|
A typical application of this function is to derive keying material for an
|
||
|
|
encryption algorithm from a password in the B<data> parameter.
|
||
|
|
|
||
|
|
Increasing the B<count> 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.
|
||
|
|
|
||
|
|
If the total key and IV length is less than the digest length and
|
||
|
|
B<MD5> is used then the derivation algorithm is compatible with PKCS#5 v1.5
|
||
|
|
otherwise a non standard extension is used to derive the extra data.
|
||
|
|
|
||
|
|
Newer applications should use more standard algorithms such as PKCS#5
|
||
|
|
v2.0 for key derivation.
|
||
|
|
|
||
|
|
=head1 KEY DERIVATION ALGORITHM
|
||
|
|
|
||
|
|
The key and IV is derived by concatenating D_1, D_2, etc until
|
||
|
|
enough data is available for the key and IV. D_i is defined as:
|
||
|
|
|
||
|
|
D_i = HASH^count(D_(i-1) || data || salt)
|
||
|
|
|
||
|
|
where || denotes concatentaion, D_0 is empty, HASH is the digest
|
||
|
|
algorithm in use, HASH^1(data) is simply HASH(data), HASH^2(data)
|
||
|
|
is HASH(HASH(data)) and so on.
|
||
|
|
|
||
|
|
The initial bytes are used for the key and the subsequent bytes for
|
||
|
|
the IV.
|
||
|
|
|
||
|
|
=head1 RETURN VALUES
|
||
|
|
|
||
|
|
EVP_BytesToKey() returns the size of the derived key in bytes.
|
||
|
|
|
||
|
|
=head1 SEE ALSO
|
||
|
|
|
||
|
|
L<evp(3)|evp(3)>, L<rand(3)|rand(3)>,
|
||
|
|
L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>,
|
||
|
|
|
||
|
|
=head1 HISTORY
|
||
|
|
|
||
|
|
=cut
|