Message Digest (hash) engine. Allows direct or incremental processing
of arbitrary length messages using a variety of hashing algorithms.
The Hash extension requires no external libraries and is enabled by
default as of PHP 5.1.2. It may be explicitly disabled by using the
--disable-hash switch to configure. Earlier versions of PHP may
incorporate the Hash extension by installing the
The constants below are defined by this extension, and
will only be available when the extension has either
been compiled into PHP or dynamically loaded at runtime.
Optional flag for hash_init().
Indicates that the HMAC digest-keying algorithm should be
applied to the current hashing context.