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.

May 22, 2018 | NetBSD 9.2