ref: 03499e53ccf8391c5b5d4b9eca096abe5e9312c3
dir: /sys/man/2/sechash/
.TH SECHASH 2
.SH NAME
md4, md5, ripemd160,
sha1, sha2_224, sha2_256, sha2_384, sha2_512,
hmac_x, hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256, hmac_sha2_384, hmac_sha2_512,
poly1305 \- cryptographically secure hashes
.SH SYNOPSIS
.nr Wd \w'\fLDS* \fP'u
.nr In \w'\fLDS* \fP'u
.ta \n(Wdu \w'\fLSHA1state* \fP'u +\n(Wdu +\n(Wdu +\n(Wdu +\n(Wdu
.
.de Ti
.PP
.in +\\n(Inu
.ti -\\n(Inu
.B
.nh
..
.
.ft L
.nf
#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>
#define DS DigestState /* only to abbreviate SYNOPSIS */
.fi
.
.Ti
DS* md4(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* md5(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* ripemd160(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* sha1(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* sha2_224(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* sha2_256(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* sha2_384(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* sha2_512(uchar *data, ulong dlen, uchar *digest, DS *state)
.Ti
DS* hmac_x(uchar *p, ulong len, uchar *key, ulong klen, uchar *digest, DS *s, DS*(*x)(uchar*, ulong, uchar*, DS*), int xlen)
.Ti
DS* hmac_md5(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* hmac_sha1(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* hmac_sha2_224(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* hmac_sha2_256(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* hmac_sha2_384(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* hmac_sha2_512(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DS *state)
.Ti
DS* poly1305(uchar *p, ulong len, uchar *key, ulong klen, uchar *digest, DS *state)
.SH DESCRIPTION
.DT
The output of a hash is called a
.IR digest .
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.
.PP
The routines
.IR md4 ,
.IR md5 ,
.IR ripemd160 ,
.IR sha1 ,
.IR sha2_224 ,
.IR sha2_256 ,
.IR sha2_384 ,
.IR sha2_512 ,
differ only in the length of the resulting digest
and in the security of the hash.
.I Sha2_*
and
.I hmac_sha2_*
are the SHA-2 functions; the number after the final underscore
is the number of bits in the resulting digest.
Usage for each is the same.
The first call to the routine should have
.B nil
as the
.I state
parameter. This call returns a state which can be used to chain
subsequent calls.
The last call should have digest
.RL non- nil .
.I Digest
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
.IR digest .
.PP
The constants
.IR MD4dlen ,
.IR MD5dlen ,
.IR RIPEMD160dlen ,
.IR SHA1dlen ,
.IR SHA2_224dlen ,
.IR SHA2_256dlen ,
.IR SHA2_384dlen ,
.I SHA2_512dlen
and
.I Poly1305dlen
define the lengths of the digests.
.PP
.IR Hmac_md5 ,
.IR hmac_sha1 ,
.IR hmac_sha2_224 ,
.IR hmac_sha2_256 ,
.IR hmac_sha2_384 ,
.I hmac_sha2_512
and
.I poly1305
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 the obvious ones from
the above list of length constants.
The
.I hmac_*
routines all call
.I hmac_x
internally, but
.I hmac_x
is not intended for general use.
.PP
.I Poly1305
is a one-time authenticator designed by D. J. Bernstein is documented in
.IR RFC8439 .
It takes a 32-byte one-time key and a message and produces a 16-byte tag.
.SH EXAMPLES
To hash a single buffer using
.IR md5 :
.IP
.EX
uchar digest[MD5dlen];
md5(data, len, digest, nil);
.EE
.PP
To chain a number of buffers together,
bounded on each end by some secret:
.IP
.EX
char buf[256];
uchar digest[MD5dlen];
DigestState *s;
s = md5("my password", 11, nil, nil);
while((n = read(fd, buf, 256)) > 0)
md5(buf, n, nil, s);
md5("drowssap ym", 11, digest, s);
.EE
.SH SOURCE
.B /sys/src/libsec
.SH SEE ALSO
.IR blowfish (2),
.IR des (2),
.IR elgamal (2),
.IR rc4 (2),
.IR rsa (2)
.PD 0
.TF /lib/rfc/rfc2104
.TP
.B /lib/rfc/rfc2104
HMAC specification