digest(3)
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 mes
sage. The digest is (usually) some small/fixed size
string. The actual size of the digest depend of the algo
rithm 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 oneway 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 inter
face. 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 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 ref
erence 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 calculate 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 origi
nally developed by Neil Winton for his "MD5" module.