NAME
hmac —
compute a key-Hash Message
Authentication Code
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
ssize_t
hmac(
const char
*hname,
const void
*key,
size_t klen,
const void *text,
size_t tlen,
void *digest,
size_t dlen);
DESCRIPTION
The
hmac() function computes the key-Hash Message
Authentication Code per RFC 2104 and places the result in
digest writing up to
dlen bytes.
The actual number of bytes that would be written is returned.
The hash functions supported are: md2, md4, md5, rmd160, sha1, sha224, sha256,
sha384, and sha512.
RETURN VALUES
The
hmac() function returns
-1
if the
hname is not found. Otherwise the actual length of the
digest string is returned (which could be bigger or smaller than
dlen). This length depends on the hashing function
selected.
SEE ALSO
md2(3),
md4(3),
md5(3),
rmd160(3),
sha1(3),
sha2(3)
STANDARDS
RFC 2104.
NOTES
The maximum digest length has been extended from
64
to
128
bytes to handle SHA2.
HISTORY
The
hmac() function appeared in
NetBSD
8.