SECHASH(3) SECHASH(3)
NAME
md4, md5, sha1, hmac_md5, hmac_sha1, md5pickle, md5unpickle,
sha1pickle, sha1unpickle - cryptographically secure hashes
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <mp.h>
#include <libsec.h>
DigestState* md4(uchar *data, ulong dlen, uchar *digest,
DigestState *state)
DigestState* md5(uchar *data, ulong dlen, uchar *digest,
DigestState *state)
char* md5pickle(MD5state *state)
MD5state* md5unpickle(char *p);
DigestState* sha1(uchar *data, ulong dlen, uchar *digest,
DigestState *state)
char* sha1pickle(MD5state *state)
MD5state* sha1unpickle(char *p);
DigestState* hmac_md5(uchar *data, ulong dlen,
uchar *key, ulong klen,
uchar *digest, DigestState *state)
DigestState* hmac_sha1(uchar *data, ulong dlen,
uchar *key, ulong klen,
uchar *digest, DigestState *state)
DESCRIPTION
These functions implement the cryptographic hash functions
MD4, MD5, and SHA1. The output of the 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, sha1, hmac_md5, and hmac_sha1 differ
only in the length of the resulting digest and in the secu-
rity of the hash. 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
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SECHASH(3) SECHASH(3)
subsequent calls. The last call should have digest non-nil.
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 digest. For example, to hash a single
buffer using md5:
uchar digest[MD5dlen];
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);
The constants MD4dlen, MD5dlen, and SHA1dlen define the
lengths of the digests.
Hmac_md5 and hmac_sha1 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
MD5dlen and SHA1dlen respectively.
The functions md5pickle and sha1pickle marshal the state of
a digest for transmission. Md5unpickle and sha1unpickle
unmarshal a pickled digest. All four routines return a
pointer to a newly malloc(3)'d object.
SOURCE
/usr/local/plan9/src/libsec
SEE ALSO
aes(3), blowfish(3), des(3), elgamal(3), rc4(3), rsa(3)
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