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.\" ========================================================================
.\"
.IX Title "EVP_BytesToKey 3openssl"
.TH EVP_BytesToKey 3openssl "2016-05-03" "1.0.1t" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_BytesToKey \- password based encryption routine
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIEVP_BytesToKey()\fR derives a key and \s-1IV\s0 from various parameters. \fBtype\fR is
the cipher to derive the key and \s-1IV\s0 for. \fBmd\fR is the message digest to use.
The \fBsalt\fR parameter is used as a salt in the derivation: it should point to
an 8 byte buffer or \s-1NULL\s0 if no salt is used. \fBdata\fR is a buffer containing
\&\fBdatal\fR bytes which is used to derive the keying data. \fBcount\fR is the
iteration count to use. The derived key and \s-1IV\s0 will be written to \fBkey\fR
and \fBiv\fR respectively.

.\" Oracle has added the ARC stability level to this manual page
.SH ATTRIBUTES
See
.BR attributes (5)
for descriptions of the following attributes:
.sp
.TS
box;
cbp-1 | cbp-1
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE 
=
Availability	library/security/openssl
=
Stability	Uncommitted
.TE 
.PP
.SH "NOTES"
.IX Header "NOTES"
A typical application of this function is to derive keying material for an
encryption algorithm from a password in the \fBdata\fR parameter.
.PP
Increasing the \fBcount\fR 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.
.PP
If the total key and \s-1IV\s0 length is less than the digest length and
\&\fB\s-1MD5\s0\fR 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.
.PP
Newer applications should use more standard algorithms such as PKCS#5
v2.0 for key derivation.
.SH "KEY DERIVATION ALGORITHM"
.IX Header "KEY DERIVATION ALGORITHM"
The key and \s-1IV\s0 is derived by concatenating D_1, D_2, etc until
enough data is available for the key and \s-1IV\s0. D_i is defined as:
.PP
.Vb 1
\&        D_i = HASH^count(D_(i\-1) || data || salt)
.Ve
.PP
where || denotes concatentaion, D_0 is empty, \s-1HASH\s0 is the digest
algorithm in use, HASH^1(data) is simply \s-1HASH\s0(data), HASH^2(data)
is \s-1HASH\s0(\s-1HASH\s0(data)) and so on.
.PP
The initial bytes are used for the key and the subsequent bytes for
the \s-1IV\s0.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIEVP_BytesToKey()\fR returns the size of the derived key in bytes.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIevp\fR\|(3), \fIrand\fR\|(3),
\&\fIEVP_EncryptInit\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"


.\" Oracle has added source availability information to this manual page
This software was built from source available at https://java.net/projects/solaris-userland.  The original community source was downloaded from  http://www.openssl.org/source/openssl-1.0.1t.tar.gz

Further information about this software can be found on the open source community website at http://www.openssl.org/.