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Digest(3pm)			 Perl Programmers Reference Guide		      Digest(3pm)

       Digest:: - Modules that calculate message digests

	 $md2 = Digest->MD2;
	 $md5 = Digest->MD5;

	 $sha1 = Digest->SHA1;
	 $sha1 = Digest->new("SHA-1");

	 $hmac = Digest->HMAC_MD5($key);

       The "Digest::" modules calculate digests, also called "fingerprints" or "hashes", of some
       data, called a message.	The digest is (usually) some small/fixed size string.  The actual
       size of the digest depend of the algorithm used.  The message is simply a sequence of
       arbitrary bytes.

       An important property of the digest algorithms is that the digest is likely to change if
       the message change in some way.	Another property is that digest functions are one-way
       functions, i.e. it should be hard to find a message that correspond to some given digest.
       Algorithms differ in how "likely" and how "hard", as well as how efficient they are to

       All "Digest::" modules provide the same programming interface.  A functional interface for
       simple use, as well as an object oriented interface that can handle messages of arbitrary
       length and which can read files directly.

       The digest can be delivered in three formats:

       binary  This is the most compact form, but it is not well suited for printing or embedding
	       in places that can't handle arbitrary data.

       hex     A twice as long string of (lowercase) hexadecimal digits.

       base64  A string of portable printable characters.  This is the base64 encoded representa-
	       tion of the digest with any trailing padding removed.  The string will be about
	       30% longer than the binary version.  MIME::Base64 tells you more about this encod-

       The functional interface is simply importable functions with the same name as the algo-
       rithm.  The functions take the message as argument and return the digest.  Example:

	 use Digest::MD5 qw(md5);
	 $digest = md5($message);

       There are also versions of the functions with "_hex" or "_base64" appended to the name,
       which returns the digest in the indicated form.

       The following methods are available for all "Digest::" modules:

       $ctx = Digest->XXX($arg,...)
       $ctx = Digest->new(XXX => $arg,...)
       $ctx = Digest::XXX->new($arg,...)
	   The constructor returns some object that encapsulate the state of the message-digest
	   algorithm.  You can add data to the object and finally ask for the digest.  The "XXX"
	   should of course be replaced by the proper name of the digest algorithm you want to

	   The two first forms are simply syntactic sugar which automatically load the right mod-
	   ule on first use.  The second form allow you to use algorithm names which contains
	   letters which are not legal perl identifiers, e.g. "SHA-1".

	   If new() is called as an instance method (i.e. $ctx->new) it will just reset the state
	   the object to the state of a newly created object.  No new object is created in this
	   case, and the return value is the reference to the object (i.e. $ctx).

	   This is just an alias for $ctx->new.

	   The $data provided as argument are appended to the message we calculate the digest
	   for.  The return value is the $ctx object itself.

	   The $io_handle is read until EOF and the content is appended to the message we calcu-
	   late the digest for.  The return value is the $ctx object itself.

	   Return the binary digest for the message.

	   Note that the "digest" operation is effectively a destructive, read-once operation.
	   Once it has been performed, the $ctx object is automatically "reset" and can be used
	   to calculate another digest value.

	   Same as $ctx->digest, but will return the digest in hexadecimal form.

	   Same as $ctx->digest, but will return the digest as a base64 encoded string.

       Digest::MD5, Digest::SHA1, Digest::HMAC, Digest::MD2


       Gisle Aas <gisle@aas.no>

       The "Digest::" interface is based on the interface originally developed by Neil Winton for
       his "MD5" module.

perl v5.8.0				    2002-06-01				      Digest(3pm)
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