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Edit File : EVP_BytesToKey.3 \| Size : 6.85 KB
.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \(-- will .\" give an unbreakable dash, \(PI will give pi, \(L" will give a left .\" double quote, and \(R" will give a right double quote. \(C+ will .\" give a nicer C++. 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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" \&\fBEVP_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. .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 perform 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 a more modern algorithm such as \s-1PBKDF2\s0 as defined in PKCS#5v2.1 and provided by \s-1PKCS5_PBKDF2_HMAC.\s0 .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 concatenation, 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" If \fBdata\fR is \s-1NULL,\s0 then \fBEVP_BytesToKey()\fR returns the number of bytes needed to store the derived key. Otherwise, \fBEVP_BytesToKey()\fR returns the size of the derived key in bytes, or 0 on error. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBevp\fR\\|(7), \fBRAND_bytes\fR\\|(3), \&\s-1\fBPKCS5_PBKDF2_HMAC\s0\fR\\|(3), \&\fBEVP_EncryptInit\fR\\|(3) .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2001\-2016 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the OpenSSL license (the \(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>. Back

Edit File : EVP_BytesToKey.3 | Size : 6.85 KB

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.\" ========================================================================
.\"
.IX Title "EVP_BYTESTOKEY 3"
.TH EVP_BYTESTOKEY 3 "2023-09-11" "1.1.1w" "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"
\&\fBEVP_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.
.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 perform 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 a more modern algorithm such as \s-1PBKDF2\s0 as
defined in PKCS#5v2.1 and provided by \s-1PKCS5_PBKDF2_HMAC.\s0
.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 concatenation, 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"
If \fBdata\fR is \s-1NULL,\s0 then \fBEVP_BytesToKey()\fR returns the number of bytes
needed to store the derived key.
Otherwise, \fBEVP_BytesToKey()\fR returns the size of the derived key in bytes,
or 0 on error.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBevp\fR\|(7), \fBRAND_bytes\fR\|(3),
\&\s-1\fBPKCS5_PBKDF2_HMAC\s0\fR\|(3),
\&\fBEVP_EncryptInit\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2001\-2016 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.

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