Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / EVP_BytesToKey.3
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124.\" ========================================================================
125.\"
126.IX Title "EVP_BytesToKey 3"
e3261593 127.TH EVP_BytesToKey 3 "2012-01-04" "1.0.0f" "OpenSSL"
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128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
984263bc 132.SH "NAME"
74dab6c2 133EVP_BytesToKey \- password based encryption routine
984263bc 134.SH "SYNOPSIS"
8b0cefbb 135.IX Header "SYNOPSIS"
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136.Vb 1
137\& #include <openssl/evp.h>
e257b235 138\&
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139\& int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md,
140\& const unsigned char *salt,
141\& const unsigned char *data, int datal, int count,
142\& unsigned char *key,unsigned char *iv);
143.Ve
144.SH "DESCRIPTION"
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145.IX Header "DESCRIPTION"
146\&\fIEVP_BytesToKey()\fR derives a key and \s-1IV\s0 from various parameters. \fBtype\fR is
147the cipher to derive the key and \s-1IV\s0 for. \fBmd\fR is the message digest to use.
984263bc 148The \fBsalt\fR paramter is used as a salt in the derivation: it should point to
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149an 8 byte buffer or \s-1NULL\s0 if no salt is used. \fBdata\fR is a buffer containing
150\&\fBdatal\fR bytes which is used to derive the keying data. \fBcount\fR is the
151iteration count to use. The derived key and \s-1IV\s0 will be written to \fBkey\fR
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152and \fBiv\fR respectively.
153.SH "NOTES"
8b0cefbb 154.IX Header "NOTES"
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155A typical application of this function is to derive keying material for an
156encryption algorithm from a password in the \fBdata\fR parameter.
157.PP
158Increasing the \fBcount\fR parameter slows down the algorithm which makes it
159harder for an attacker to peform a brute force attack using a large number
160of candidate passwords.
161.PP
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162If the total key and \s-1IV\s0 length is less than the digest length and
163\&\fB\s-1MD5\s0\fR is used then the derivation algorithm is compatible with PKCS#5 v1.5
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164otherwise a non standard extension is used to derive the extra data.
165.PP
166Newer applications should use more standard algorithms such as PKCS#5
167v2.0 for key derivation.
168.SH "KEY DERIVATION ALGORITHM"
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169.IX Header "KEY DERIVATION ALGORITHM"
170The key and \s-1IV\s0 is derived by concatenating D_1, D_2, etc until
171enough data is available for the key and \s-1IV\s0. D_i is defined as:
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172.PP
173.Vb 1
e257b235 174\& D_i = HASH^count(D_(i\-1) || data || salt)
984263bc 175.Ve
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176.PP
177where || denotes concatentaion, D_0 is empty, \s-1HASH\s0 is the digest
178algorithm in use, HASH^1(data) is simply \s-1HASH\s0(data), HASH^2(data)
179is \s-1HASH\s0(\s-1HASH\s0(data)) and so on.
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180.PP
181The initial bytes are used for the key and the subsequent bytes for
8b0cefbb 182the \s-1IV\s0.
984263bc 183.SH "RETURN VALUES"
74dab6c2 184.IX Header "RETURN VALUES"
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185\&\fIEVP_BytesToKey()\fR returns the size of the derived key in bytes.
186.SH "SEE ALSO"
74dab6c2 187.IX Header "SEE ALSO"
8b0cefbb 188\&\fIevp\fR\|(3), \fIrand\fR\|(3),
a561f9ff 189\&\fIEVP_EncryptInit\fR\|(3)
8b0cefbb 190.SH "HISTORY"
984263bc 191.IX Header "HISTORY"