Digest::MD5(3perl)

📦
version 5.44.0 · 14 versions
, in arch rolling

💖 Digest::MD5 💖

okay bestie, sit down, hydrate, because we're doing the Digest::MD5 glow-up. ✨ This is the Perl interface to the MD5 Algorithm, and it lives in the Perl Programmers Reference Guide, section 3perl. It's giving classic. It's giving vintage. It's giving "yes queen, hash that string." 🎀

🌸 NAME 🌸

Digest::MD5 — Perl interface to the MD5 Algorithm. That's the whole name, no notes. 💅

✨ SYNOPSIS ✨

Two ways to serve this lewk: the functional style, and the OO style. Pick your fighter. 🥊

# Functional style
use Digest::MD5 qw(md5 md5_hex md5_base64);

my $digest = md5($data);
my $digest = md5_hex($data);
my $digest = md5_base64($data);

# OO style
use Digest::MD5;

my $ctx = Digest::MD5->new;

$ctx->add($data);
$ctx->addfile($file_handle);

$digest = $ctx->digest;
$digest = $ctx->hexdigest;
$digest = $ctx->b64digest;

🦋 DESCRIPTION 🦋

So basically ✨ the Digest::MD5 module lets you use the RSA Data Security Inc. MD5 Message Digest algorithm from right inside your Perl programs. The algorithm takes a message of any length as input and produces, as output, a 128-bit "fingerprint" or "message digest" of that input. Cute, right? 🫶

😭 okay so we have to talk about it: the MD5 algorithm is not as strong as it used to be. Since 2005 it has been easy to generate different messages that produce the same MD5 digest. It still seems hard to generate messages that produce a given digest, but it's probably wise to move to stronger algorithms for applications that depend on the digest to uniquely identify a message. Please hear me on this one bestie, it's not a vibe, it's a security thing. 🔥

The Digest::MD5 module provides a procedural interface for simple use, plus an object oriented interface that can handle messages of arbitrary length and which can read files directly. Main character options, honestly. 👑

💜 FUNCTIONS 💜

These functions are provided by the Digest::MD5 module. Bestie, heads up: none of these functions are exported by default. You gotta ask for them. 🙈

  • md5($data,...) — this one concatenates all its arguments, calculates the MD5 digest of that whole "message", and hands it back in binary form. The returned string will be 16 bytes long. 💖 The result of md5("a", "b", "c") will be exactly the same as the result of md5("abc"). Same energy, same digest. ✨
  • md5_hex($data,...) — same as md5(), but returns the digest in hexadecimal form. The length of the returned string will be 32, and it will only contain characters from this set: '0'..'9' and 'a'..'f'. No cap. 🔥
  • md5_base64($data,...) — same as md5(), but returns the digest as a base64 encoded string. The length of the returned string will be 22, and it will only contain characters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+' and '/'. 🌈
👀 lowkey important: the base64 encoded string returned is not padded to be a multiple of 4 bytes long. If you want interoperability with other base64 encoded md5 digests you might want to append the redundant string "==" to the result.

🎀 METHODS 🎀

The object oriented interface to Digest::MD5 lives right here, bestie. Once a Digest::MD5 object has been created, you add data to it and finally ask for the digest in whatever format suits the moment. And the slay part: a single object can be used to calculate multiple digests. Reusable queen. 💅

The following methods are provided:

  • $md5 = Digest::MD5->new — the constructor returns a new Digest::MD5 object which encapsulates the state of the MD5 message-digest algorithm. 🌸 If it's called as an instance method (i.e. $md5->new) it will just reset the state of the object back to the state of a newly created object. No new object is created in this case. It's a reset, not a rebirth. 🦋
  • $md5->reset — this is just an alias for $md5->new. Same thing, different font. 💅
  • $md5->clone — this is a copy of the $md5 object. It's useful when you don't want to destroy the digest's state, but you need an intermediate value of the digest, e.g. when calculating digests iteratively on a continuous data stream. Example, because we love an example:
my $md5 = Digest::MD5->new;
while (<>) {
    $md5->add($_);
    print "Line $.: ", $md5->clone->hexdigest, "\n";
}
  • $md5->add($data,...) — the $data you pass as arguments get appended to the message we're calculating the digest for. The return value is the $md5 object itself. (Chainable, we love to see it. ✨)

All these lines will have the same effect on the state of the $md5 object:

$md5->add("a"); $md5->add("b"); $md5->add("c");
$md5->add("a")->add("b")->add("c");
$md5->add("a", "b", "c");
$md5->add("abc");
  • $md5->addfile($io_handle) — the $io_handle will be read until EOF, and its content appended to the message we're calculating the digest for. The return value is the $md5 object itself. 💖
😭 okay so: the addfile() method will croak() if it fails reading data for some reason. If it croaks, it is unpredictable what the state of the $md5 object will be in. The addfile() method might have been able to read the file partially before it failed. It is probably wise to discard or reset the $md5 object if this occurs. Like, it's in its flop era at that point, just start over. 💀

In most cases you want to make sure the $io_handle is in "binmode" before you pass it as an argument to the addfile() method. 🌸

  • $md5->add_bits($data, $nbits)
  • $md5->add_bits($bitstring) — since the MD5 algorithm is byte oriented, you might only add bits as multiples of 8, so you probably want to just use add() instead. The add_bits() method is provided for compatibility with other digest implementations. See Digest for a description of the arguments that add_bits() takes. 🙈
  • $md5->digest — return the binary digest for the message. The returned string will be 16 bytes long. 💖
👑 note that the "digest" operation is effectively a destructive, read-once operation. Once it has been performed, the Digest::MD5 object is automatically "reset" and can be used to calculate another digest value. Call $md5->clone->digest if you want to calculate the digest without resetting the digest state. The way that it just resets itself... iconic but also a jumpscare if you're not ready. 🌈
  • $md5->hexdigest — same as $md5->digest, but returns the digest in hexadecimal form. The length of the returned string will be 32, and it will only contain characters from this set: '0'..'9' and 'a'..'f'. ✨
  • $md5->b64digest — same as $md5->digest, but returns the digest as a base64 encoded string. The length of the returned string will be 22, and it will only contain characters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+' and '/'. 🌸
The base64 encoded string returned is not padded to be a multiple of 4 bytes long. If you want interoperability with other base64 encoded md5 digests you might want to append the string "==" to the result.
  • @ctx = $md5->context
  • $md5->context(@ctx) — saves or restores the internal state. When called with no arguments, it returns a list: number of blocks processed, a 16-byte internal state buffer, then optionally up to 63 bytes of unprocessed data if there are any. When passed those same arguments, it restores the state. This is only useful for specialised operations. It's giving secret menu. 🤫

🌈 EXAMPLES 🌈

The simplest way to use this library is to import the md5_hex() function (or one of its cousins). Cousins! 🫶

use Digest::MD5 qw(md5_hex);
print "Digest is ", md5_hex("foobarbaz"), "\n";

The above example would print out the message:

Digest is 6df23dc03f9b54cc38a0fc1483df6e21

The same checksum can also be calculated in OO style:

use Digest::MD5;
my $md5 = Digest::MD5->new;
$md5->add('foo', 'bar');
$md5->add('baz');
my $digest = $md5->hexdigest;
print "Digest is $digest\n";

With OO style, you can break the message arbitrarily. This means we are no longer limited to having space for the whole message in memory, i.e. we can handle messages of any size. Unhinged amounts of data? Handled. 💅

This is useful when calculating a checksum for files:

use Digest::MD5;

my $filename = shift || "/etc/passwd";
open (my $fh, '<', $filename) or die "Can't open '$filename': $!";
binmode($fh);

my $md5 = Digest::MD5->new;
while (<$fh>) {
    $md5->add($_);
}
close($fh);
print $md5->b64digest, " $filename\n";

Or we can use the addfile method for a more efficient reading of the file:

use Digest::MD5;

my $filename = shift || "/etc/passwd";
open (my $fh, '<', $filename) or die "Can't open '$filename': $!";
binmode ($fh);

print Digest::MD5->new->addfile($fh)->hexdigest, " $filename\n";

Since the MD5 algorithm is only defined for strings of bytes, it can not be used on strings that contain chars with ordinal number above 255 (Unicode strings). The MD5 functions and methods will croak if you try to feed them such input data: 😭

use Digest::MD5 qw(md5_hex);

my $str = "abc\x{300}";
print md5_hex($str), "\n";  # croaks
# Wide character in subroutine entry

What you can do is calculate the MD5 checksum of the UTF-8 representation of such strings. This is achieved by filtering the string through the encode_utf8() function:

use Digest::MD5 qw(md5_hex);
use Encode qw(encode_utf8);

my $str = "abc\x{300}";
print md5_hex(encode_utf8($str)), "\n";
# 8c2d46911f3f5a326455f0ed7a8ed3b3

💫 SEE ALSO 💫

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

 Copyright 1998-2003 Gisle Aas.
 Copyright 1995-1996 Neil Winton.
 Copyright 1991-1992 RSA Data Security, Inc.

The MD5 algorithm is defined in RFC 1321. This implementation is derived from the reference C code in RFC 1321, which is covered by the following copyright statement:

  • Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All rights reserved.

License to copy and use this software is granted provided that it is identified as the "RSA Data Security, Inc. MD5 Message-Digest Algorithm" in all material mentioning or referencing this software or this function.

License is also granted to make and use derivative works provided that such works are identified as "derived from the RSA Data Security, Inc. MD5 Message-Digest Algorithm" in all material mentioning or referencing the derived work.

RSA Data Security, Inc. makes no representations concerning either the merchantability of this software or the suitability of this software for any particular purpose. It is provided "as is" without express or implied warranty of any kind.

These notices must be retained in any copies of any part of this documentation and/or software.

This copyright does not prohibit distribution of any version of Perl containing this extension under the terms of the GNU or Artistic licenses.

to be continued, bestie… 🦋

💖 AUTHORS 💖

okay so bestie, let's give credit where credit is due, because these two ate and left no crumbs 👑

  • The original MD5 interface was written by Neil Winton (N.Winton@axion.bt.co.uk).
  • The Digest::MD5 module is written by Gisle Aas <gisle@ActiveState.com>.

that's the whole roster, no cap. two absolute icons, one legendary module 🫶✨ literally the blueprint fr fr.

and that's a wrap on this page, bestie!! 💅🌸 you just read the Digest::MD5 manual as shipped in perl v5.44.0, dated 2026-10-17 — yeah, from the future, iconic behavior honestly 🦋 go forth and hash responsibly, mwah 😭💜🎀

📦 where this page comes from