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[dragonfly.git] / secure / lib / libcrypto / man / EVP_BytesToKey.3
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2''' $RCSfile$$Revision$$Date$
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34'''
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36''' Set up \*(-- to give an unbreakable dash;
37''' string Tr holds user defined translation string.
38''' Bell System Logo is used as a dummy character.
39'''
984263bc 40.tr \(*W-|\(bv\*(Tr
984263bc 41.ie n \{\
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42.ds -- \(*W-
43.ds PI pi
44.if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
45.if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
46.ds L" ""
47.ds R" ""
48''' \*(M", \*(S", \*(N" and \*(T" are the equivalent of
49''' \*(L" and \*(R", except that they are used on ".xx" lines,
50''' such as .IP and .SH, which do another additional levels of
51''' double-quote interpretation
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64.ds -- \(em\|
65.tr \*(Tr
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80.\" If the F register is turned on, we'll generate
81.\" index entries out stderr for the following things:
82.\" TH Title
83.\" SH Header
84.\" Sh Subsection
85.\" Ip Item
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87.\" Of course, you have to process the output yourself
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96.TH EVP_BytesToKey 3 "0.9.7d" "2/Sep/2004" "OpenSSL"
97.UC
98.if n .hy 0
984263bc 99.if n .na
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109..
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115. ds #H 0
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120.\}
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139.\}
140.if t \{\
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141. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
142. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
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145. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
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147. ds ! \s-2\(or\s+2\h'-\w'\(or'u'\v'-.8m'.\v'.8m'
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172\{\
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188.\}
189.rm #[ #] #H #V #F C
984263bc 190.SH "NAME"
74dab6c2 191EVP_BytesToKey \- password based encryption routine
984263bc 192.SH "SYNOPSIS"
74dab6c2 193.PP
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194.Vb 1
195\& #include <openssl/evp.h>
196.Ve
197.Vb 4
198\& int EVP_BytesToKey(const EVP_CIPHER *type,const EVP_MD *md,
199\& const unsigned char *salt,
200\& const unsigned char *data, int datal, int count,
201\& unsigned char *key,unsigned char *iv);
202.Ve
203.SH "DESCRIPTION"
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204\fIEVP_BytesToKey()\fR derives a key and IV from various parameters. \fBtype\fR is
205the cipher to derive the key and IV for. \fBmd\fR is the message digest to use.
984263bc 206The \fBsalt\fR paramter is used as a salt in the derivation: it should point to
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207an 8 byte buffer or NULL if no salt is used. \fBdata\fR is a buffer containing
208\fBdatal\fR bytes which is used to derive the keying data. \fBcount\fR is the
209iteration count to use. The derived key and IV will be written to \fBkey\fR
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210and \fBiv\fR respectively.
211.SH "NOTES"
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212A typical application of this function is to derive keying material for an
213encryption algorithm from a password in the \fBdata\fR parameter.
214.PP
215Increasing the \fBcount\fR parameter slows down the algorithm which makes it
216harder for an attacker to peform a brute force attack using a large number
217of candidate passwords.
218.PP
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219If the total key and IV length is less than the digest length and
220\fBMD5\fR is used then the derivation algorithm is compatible with PKCS#5 v1.5
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221otherwise a non standard extension is used to derive the extra data.
222.PP
223Newer applications should use more standard algorithms such as PKCS#5
224v2.0 for key derivation.
225.SH "KEY DERIVATION ALGORITHM"
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226The key and IV is derived by concatenating D_1, D_2, etc until
227enough data is available for the key and IV. D_i is defined as:
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228.PP
229.Vb 1
230\& D_i = HASH^count(D_(i-1) || data || salt)
231.Ve
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232where || denotes concatentaion, D_0 is empty, HASH is the digest
233algorithm in use, HASH^\fI1\fR\|(data) is simply \fIHASH\fR\|(data), HASH^\fI2\fR\|(data)
234is \fIHASH\fR\|(HASH(data)) and so on.
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235.PP
236The initial bytes are used for the key and the subsequent bytes for
74dab6c2 237the IV.
984263bc 238.SH "RETURN VALUES"
74dab6c2 239\fIEVP_BytesToKey()\fR returns the size of the derived key in bytes.
984263bc 240.SH "SEE ALSO"
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241evp(3), rand(3),
242EVP_EncryptInit(3),
243.SH "HISTORY"
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244
245.rn }` ''
246.IX Title "EVP_BytesToKey 3"
247.IX Name "EVP_BytesToKey - password based encryption routine"
248
249.IX Header "NAME"
250
251.IX Header "SYNOPSIS"
252
253.IX Header "DESCRIPTION"
254
255.IX Header "NOTES"
256
257.IX Header "KEY DERIVATION ALGORITHM"
258
259.IX Header "RETURN VALUES"
260
261.IX Header "SEE ALSO"
262
984263bc 263.IX Header "HISTORY"
74dab6c2 264