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HMAC(3)                    Library Functions Manual                    HMAC(3)

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), openssl_HMAC(3), openssl_MD2(3), openssl_MD4(3),
     openssl_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.

NetBSD 10.99                     May 22, 2018                     NetBSD 10.99