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<head>
<title>sechash(3) - Plan 9 from User Space</title>
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<tr><td width=20><td>
<tr><td width=20><td><b>SECHASH(3)</b><td align=right><b>SECHASH(3)</b>
<tr><td width=20><td colspan=2>
<br>
<p><font size=+1><b>NAME </b></font><br>
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md4, md5, sha1, hmac_md5, hmac_sha1, md5pickle, md5unpickle, sha1pickle,
sha1unpickle – cryptographically secure hashes<br>
</table>
<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>#include <u.h><br>
#include <libc.h><br>
#include <mp.h><br>
#include <libsec.h>
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</font></tt>
<tt><font size=+1>DigestState* md4(uchar *data, ulong dlen, uchar *digest, DigestState
*state)
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</font></tt>
<tt><font size=+1>DigestState* md5(uchar *data, ulong dlen, uchar *digest, DigestState
*state)
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</font></tt>
<tt><font size=+1>char* md5pickle(MD5state *state)
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</font></tt>
<tt><font size=+1>MD5state* md5unpickle(char *p);
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</font></tt>
<tt><font size=+1>DigestState* sha1(uchar *data, ulong dlen, uchar *digest, DigestState
*state)
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</font></tt>
<tt><font size=+1>char* sha1pickle(MD5state *state)
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</font></tt>
<tt><font size=+1>MD5state* sha1unpickle(char *p);
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</font></tt>
<tt><font size=+1>DigestState* hmac_md5(uchar *data, ulong dlen,<br>
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uchar *key, ulong klen,<br>
uchar *digest, DigestState *state)
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</table>
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</font></tt>
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<tt><font size=+1>DigestState* hmac_sha1(uchar *data, ulong dlen,<br>
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uchar *key, ulong klen,<br>
uchar *digest, DigestState *state)<br>
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</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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These functions implement the cryptographic hash functions MD4,
MD5, and SHA1. The output of the hash is called a <i>digest</i>. A hash
is secure if, given the hashed data and the digest, it is difficult
to predict the change to the digest resulting from some change
to the data without rehashing the whole data. Therefore, if
a secret is part of the hashed data, the digest can be used as
an integrity check of the data by anyone possessing the secret.
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The routines <i>md4</i>, <i>md5</i>, <i>sha1</i>, <i>hmac_md5</i>, and <i>hmac_sha1</i> differ only
in the length of the resulting digest and in the security of the
hash. Usage for each is the same. The first call to the routine
should have <tt><font size=+1>nil</font></tt> as the <i>state</i> parameter. This call returns a state
which can be used to chain subsequent calls. The last call
should have digest non-nil. <i>Digest</i> must point to a buffer of at
least the size of the digest produced. This last call will free
the state and copy the result into <i>digest</i>. For example, to hash
a single buffer using <i>md5</i>:<br>
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<tt><font size=+1>uchar digest[MD5dlen];<br>
md5(data, len, digest, nil);<br>
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</font></tt>
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To chain a number of buffers together, bounded on each end by
some secret:<br>
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<tt><font size=+1>char buf[256];<br>
uchar digest[MD5dlen];<br>
DigestState *s;<br>
s = md5("my password", 11, nil, nil);<br>
while((n = read(fd, buf, 256)) > 0)<br>
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md5(buf, n, nil, s);<br>
</table>
md5("drowssap ym", 11, digest, s);<br>
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</font></tt>
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The constants <i>MD4dlen</i>, <i>MD5dlen</i>, and <i>SHA1dlen</i> define the lengths
of the digests.
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<i>Hmac_md5</i> and <i>hmac_sha1</i> are used slightly differently. These hash
algorithms are keyed and require a key to be specified on every
call. The digest lengths for these hashes are <i>MD5dlen</i> and <i>SHA1dlen</i>
respectively.
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The functions <i>md5pickle</i> and <i>sha1pickle</i> marshal the state of a
digest for transmission. <i>Md5unpickle</i> and <i>sha1unpickle</i> unmarshal
a pickled digest. All four routines return a pointer to a newly
<a href="../man3/malloc.html"><i>malloc</i>(3)</a>’d object.<br>
</table>
<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/libsec<br>
</font></tt>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<a href="../man3/aes.html"><i>aes</i>(3)</a>, <a href="../man3/blowfish.html"><i>blowfish</i>(3)</a>, <a href="../man3/des.html"><i>des</i>(3)</a>, <a href="../man3/elgamal.html"><i>elgamal</i>(3)</a>, <a href="../man3/rc4.html"><i>rc4</i>(3)</a>, <a href="../man3/rsa.html"><i>rsa</i>(3)</a><br>
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