SECHASH(2) SECHASH(2)
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
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>
#define DS DigestState /* only to abbreviate SYNOPSIS */
DS* md4(uchar *data, ulong dlen, uchar *digest, DS *state)
DS* md5(uchar *data, ulong dlen, uchar *digest, DS *state)
DS* ripemd160(uchar *data, ulong dlen, uchar *digest, DS
*state)
DS* sha1(uchar *data, ulong dlen, uchar *digest, DS *state)
DS* sha2_224(uchar *data, ulong dlen, uchar *digest, DS
*state)
DS* sha2_256(uchar *data, ulong dlen, uchar *digest, DS
*state)
DS* sha2_384(uchar *data, ulong dlen, uchar *digest, DS
*state)
DS* sha2_512(uchar *data, ulong dlen, uchar *digest, DS
*state)
DS* hmac_x(uchar *p, ulong len, uchar *key, ulong klen,
uchar *digest, DS *s, DS*(*x)(uchar*, ulong, uchar*,
DS*), int xlen)
DS* hmac_md5(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
DS* hmac_sha1(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
DS* hmac_sha2_224(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
DS* hmac_sha2_256(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
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SECHASH(2) SECHASH(2)
DS* hmac_sha2_384(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
DS* hmac_sha2_512(uchar *data, ulong dlen, uchar *key, ulong
klen, uchar *digest, DS *state)
DS* poly1305(uchar *p, ulong len, uchar *key, ulong klen,
uchar *digest, DS *state)
DESCRIPTION
The output of a hash is called a 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.
The routines md4, md5, ripemd160, sha1, sha2_224, sha2_256,
sha2_384, sha2_512, differ only in the length of the result-
ing digest and in the security of the hash. Sha2_* and
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 nil as the state parameter. This call
returns a state which can be used to chain subsequent calls.
The last call should have digest non-`nil'. Digest must
point to a buffer of at least the size of the digest pro-
duced. This last call will free the state and copy the
result into digest.
The constants MD4dlen, MD5dlen, RIPEMD160dlen, SHA1dlen,
SHA2_224dlen, SHA2_256dlen, SHA2_384dlen, SHA2_512dlen and
Poly1305dlen define the lengths of the digests.
Hmac_md5, hmac_sha1, hmac_sha2_224, hmac_sha2_256,
hmac_sha2_384, hmac_sha2_512 and 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 hmac_* routines all call hmac_x
internally, but hmac_x is not intended for general use.
Poly1305 is a one-time authenticator designed by D. J. Bern-
stein is documented in RFC8439. It takes a 32-byte one-time
key and a message and produces a 16-byte tag.
EXAMPLES
To hash a single buffer using md5:
uchar digest[MD5dlen];
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SECHASH(2) SECHASH(2)
md5(data, len, digest, nil);
To chain a number of buffers together, bounded on each end
by some secret:
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);
SOURCE
/sys/src/libsec
SEE ALSO
blowfish(2), des(2), elgamal(2), rc4(2), rsa(2)
/lib/rfc/rfc2104 HMAC specification
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