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EVP_BYTESTOKEY(3)		    OpenSSL		     EVP_BYTESTOKEY(3)

NAME
       EVP_BytesToKey -	password based encryption routine

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);

DESCRIPTION
       EVP_BytesToKey()	derives	a key and IV from various parameters. type is
       the cipher to derive the	key and	IV for.	md is the message digest to
       use.  The salt parameter	is used	as a salt in the derivation: it	should
       point to	an 8 byte buffer or NULL if no salt is used. data is a buffer
       containing datal	bytes which is used to derive the keying data. count
       is the iteration	count to use. The derived key and IV will be written
       to key and iv respectively.

NOTES
       A typical application of	this function is to derive keying material for
       an encryption algorithm from a password in the data parameter.

       Increasing the count parameter slows down the algorithm which makes it
       harder for an attacker to perform 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 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 a more modern algorithm such as PBKDF2 as
       defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC.

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	concatenation, 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.

RETURN VALUES
       If data is NULL,	then EVP_BytesToKey() returns the number of bytes
       needed to store the derived key.	 Otherwise, EVP_BytesToKey() returns
       the size	of the derived key in bytes, or	0 on error.

SEE ALSO
       evp(7), RAND_bytes(3), PKCS5_PBKDF2_HMAC(3), EVP_EncryptInit(3)

COPYRIGHT
       Copyright 2001-2016 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (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
       <https://www.openssl.org/source/license.html>.

1.1.1d				  2019-09-10		     EVP_BYTESTOKEY(3)

NAME | SYNOPSIS | DESCRIPTION | NOTES | KEY DERIVATION ALGORITHM | RETURN VALUES | SEE ALSO | COPYRIGHT

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