1=pod 2 3=head1 NAME 4 5EVP_BytesToKey - password based encryption routine 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 11 int EVP_BytesToKey(const EVP_CIPHER *type, const EVP_MD *md, 12 const unsigned char *salt, 13 const unsigned char *data, int datal, int count, 14 unsigned char *key, unsigned char *iv); 15 16=head1 DESCRIPTION 17 18EVP_BytesToKey() derives a key and IV from various parameters. B<type> is 19the cipher to derive the key and IV for. B<md> is the message digest to use. 20The B<salt> parameter is used as a salt in the derivation: it should point to 21an 8 byte buffer or NULL if no salt is used. B<data> is a buffer containing 22B<datal> bytes which is used to derive the keying data. B<count> is the 23iteration count to use. The derived key and IV will be written to B<key> 24and B<iv> respectively. 25 26=head1 NOTES 27 28A typical application of this function is to derive keying material for an 29encryption algorithm from a password in the B<data> parameter. 30 31Increasing the B<count> parameter slows down the algorithm which makes it 32harder for an attacker to perform a brute force attack using a large number 33of candidate passwords. 34 35If the total key and IV length is less than the digest length and 36B<MD5> is used then the derivation algorithm is compatible with PKCS#5 v1.5 37otherwise a non standard extension is used to derive the extra data. 38 39Newer applications should use a more modern algorithm such as PBKDF2 as 40defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC. 41 42=head1 KEY DERIVATION ALGORITHM 43 44The key and IV is derived by concatenating D_1, D_2, etc until 45enough data is available for the key and IV. D_i is defined as: 46 47 D_i = HASH^count(D_(i-1) || data || salt) 48 49where || denotes concatenation, D_0 is empty, HASH is the digest 50algorithm in use, HASH^1(data) is simply HASH(data), HASH^2(data) 51is HASH(HASH(data)) and so on. 52 53The initial bytes are used for the key and the subsequent bytes for 54the IV. 55 56=head1 RETURN VALUES 57 58If B<data> is NULL, then EVP_BytesToKey() returns the number of bytes 59needed to store the derived key. 60Otherwise, EVP_BytesToKey() returns the size of the derived key in bytes, 61or 0 on error. 62 63=head1 SEE ALSO 64 65L<evp(7)>, L<RAND_bytes(3)>, 66L<PKCS5_PBKDF2_HMAC(3)>, 67L<EVP_EncryptInit(3)> 68 69=head1 COPYRIGHT 70 71Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved. 72 73Licensed under the Apache License 2.0 (the "License"). You may not use 74this file except in compliance with the License. You can obtain a copy 75in the file LICENSE in the source distribution or at 76L<https://www.openssl.org/source/license.html>. 77 78=cut 79
