Seth Woolley's Man Viewer

Digest(3) - Digest - Modules that calculate message digests - man 3 Digest

([section] manual, -k keyword, -K [section] search, -f whatis)
man plain no title

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



NAME
       Digest - Modules that calculate message digests

SYNOPSIS
         $md5(1,3,1 dgst)  = Digest->new("MD5");
         $sha1 = Digest->new("SHA-1");
         $sha256 = Digest->new("SHA-256");
         $sha384 = Digest->new("SHA-384");
         $sha512 = Digest->new("SHA-512");

         $hmac = Digest->HMAC_MD5($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 or
       bits.

       An important property of the digest algorithms is that the digest is
       likely to change if(3,n) the message change in(1,8) 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(1,8) 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(2,n,1 builtins)
       files directly.

       The digest can be delivered in(1,8) three formats:

       binary  This is the most compact form, but it is not well suited for
               printing or embedding in(1,8) places that can't handle arbitrary
               data.

       hex     A twice as long string(3,n) of lowercase hexadecimal digits.

       base64  A string(3,n) of portable printable characters.  This is the base64
               encoded representation of the digest with any trailing padding
               removed.  The string(3,n) 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(1,3,1 dgst));
         $digest = md5(1,3,1 dgst)($message);

       There are also versions of the functions with "_hex" or "_base64"
       appended to the name, which returns the digest in(1,8) 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(7,n) 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 no implementation for the given
           algorithm can be found, then an exception is raised.

           If new() is called as an instance method (i.e. $ctx->new) it will
           just reset(1,7,1 tput) the state the object to the state of a newly created
           object.  No new object is created in(1,8) this case, and the return
           value is the reference to the object (i.e. $ctx).

       $other_ctx = $ctx->clone
           The clone method creates a copy of the digest state object and
           returns a reference to the copy.

       $ctx->reset(1,7,1 tput)
           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(2,n,1 builtins) until EOF and the content is appended to the
           message we calculate the digest for.  The return value is the $ctx
           object itself.

       $ctx->add_bits( $data, $nbits )
       $ctx->add_bits( $bitstring )
           The bits provided are appended to the message we calculate the
           digest for.  The return value is the $ctx object itself.

           The two argument form of add_bits() will add the first $nbits bits
           from data.  For the last potentially partial byte only the high
           order "$nbits % 8" bits are used.  If $nbits is greater than
           "length($data) * 8", then this method would do the same as
           "$ctx->add($data)", i.e. $nbits is silently ignored.

           The one argument form of add_bits() takes a $bitstring of "1" and
           "0" chars as argument.  It's a shorthand for
           "$ctx->add_bits(pack(3,n,n pack-old)("B*", $bitstring), length($bitstring))".

           This example shows two calls that should have the same effect:

              $ctx->add_bits("111100001010");
              $ctx->add_bits("\xF0\xA0", 12);

           Most digest algorithms are byte based.  For those it is not possi-
           ble to add bits that are not a multiple of 8, and the add_bits()
           method will croak if(3,n) you try.

       $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(1,7,1 tput)" and can be used to calculate another digest
           value.  Call $ctx->clone->digest if(3,n) you want to calculate the
           digest without reseting the digest state.

       $ctx->hexdigest
           Same as $ctx->digest, but will return the digest in(1,8) hexadecimal
           form.

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

Digest speed
       This table should give some indication on the relative speed of differ-
       ent algorithms.  It is sorted by throughput based on a benchmark done
       with of some implementations of this API:

        Algorithm      Size    Implementation                  MB/s

        MD4            128     Digest::MD4 v1.3               165.0
        MD5            128     Digest::MD5 v2.33               98.8
        SHA-256        256     Digest::SHA2 v1.1.0             66.7
        SHA-1          160     Digest::SHA v4.3.1              58.9
        SHA-1          160     Digest::SHA1 v2.10              48.8
        SHA-256        256     Digest::SHA v4.3.1              41.3
        Haval-256      256     Digest::Haval256 v1.0.4         39.8
        SHA-384        384     Digest::SHA2 v1.1.0             19.6
        SHA-512        512     Digest::SHA2 v1.1.0             19.3
        SHA-384        384     Digest::SHA v4.3.1              19.2
        SHA-512        512     Digest::SHA v4.3.1              19.2
        Whirlpool      512     Digest::Whirlpool v1.0.2        13.0
        MD2            128     Digest::MD2 v2.03                9.5

        Adler-32        32     Digest::Adler32 v0.03            1.3
        CRC-16          16     Digest::CRC v0.05                1.1
        CRC-32          32     Digest::CRC v0.05                1.1
        MD5            128     Digest::Perl::MD5 v1.5           1.0
        CRC-CCITT       16     Digest::CRC v0.05                0.8

       These numbers was achieved Apr 2004 with ActivePerl-5.8.3 running under
       Linux on a P4 2.8 GHz CPU.  The last 5 entries differ by being pure
       perl implementations of the algorithms, which explains why they are so
       slow.

SEE ALSO
       Digest::Adler32, Digest::CRC, Digest::Haval256, Digest::HMAC,
       Digest::MD2, Digest::MD4, Digest::MD5, Digest::SHA, Digest::SHA1,
       Digest::SHA2, Digest::Whirlpool

       New digest implementations should consider subclassing from
       Digest::base.

       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.

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

           Copyright 1998-2001,2003-2004 Gisle Aas.
           Copyright 1995-1996 Neil Winton.



perl v5.8.5                       2001-09-21                         Digest(3)

References for this manual (incoming links)