/usr/man/cat.3/Digest.3.Z(/usr/man/cat.3/Digest.3.Z)

NAME

       Digest:: - Modules that calculate message digests

SYNOPSIS

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

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

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

DESCRIPTION

       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 compute.

       All "Digest::" modules provide the same programming interface.  A func-
       tional interface for simple use, as well as an object oriented inter-
       face 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 representation 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 encoding.

       The functional interface is simply importable functions with the same
       name as the algorithm.  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.

OO INTERFACE

       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 use.

           The two first forms are simply syntactic sugar which automatically
           load the right module 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).

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

       $ctx->add($data,...)
           The $data provided as argument are appended to the message we cal-
           culate the digest for.  The return value is the $ctx object itself.

       $ctx->addfile($io_handle)
           The $io_handle is read until EOF and the content is appended to the
           message we calculate the digest for.  The return value is the $ctx
           object itself.

       $ctx->digest
           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.

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

       $ctx->b64digest
           Same as $ctx->digest, but will return the digest as a base64
           encoded string.

SEE ALSO

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

       MIME::Base64

AUTHOR

       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(3)
See also Digest::MD5(3):  man 3 Digest::MD5