Digest(3p) Perl Programmers Reference Guide Digest(3p) #
Digest(3p) Perl Programmers Reference Guide Digest(3p)
NNAAMMEE #
Digest - Modules that calculate message digests
SSYYNNOOPPSSIISS #
$md5 = 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);
DDEESSCCRRIIPPTTIIOONN #
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
_l_i_k_e_l_y to change if the message change in some way. Another property is
that digest functions are one-way functions, that is it should be _h_a_r_d 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.
Note that the properties of the algorithms change over time, as the
algorithms are analyzed and machines grow faster. If your application
for instance depends on it being "impossible" to generate the same digest
for a different message it is wise to make it easy to plug in stronger
algorithms as the one used grow weaker. Using the interface documented
here should make it easy to change algorithms later.
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:
_b_i_n_a_r_y This is the most compact form, but it is not well suited for
printing or embedding in places that can't handle arbitrary data.
_h_e_x A twice as long string of lowercase hexadecimal digits.
_b_a_s_e_6_4 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.
OOOO IINNTTEERRFFAACCEE #
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 no implementation for the given
algorithm can be found, then an exception is raised.
To know what arguments (if any) the constructor takes (the
"$args,..." above) consult the docs for the specific digest
implementation.
If nneeww(()) 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).
$other_ctx = $ctx->clone
The clone method creates a copy of the digest state object and
returns a reference to the copy.
$ctx->reset
This is just an alias for $ctx->new.
$ctx->add( $data )
$ctx->add( $chunk1, $chunk2, ... )
The string value of the $data provided as argument is appended to the
message we calculate the digest for. The return value is the $ctx
object itself.
If more arguments are provided then they are all appended to the
message, thus all these lines will have the same effect on the state
of the $ctx object:
$ctx->add("a"); $ctx->add("b"); $ctx->add("c");
$ctx->add("a")->add("b")->add("c");
$ctx->add("a", "b", "c");
$ctx->add("abc");
Most algorithms are only defined for strings of bytes and this method
might therefore croak if the provided arguments contain chars with
ordinal number above 255.
$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.
The aaddddffiillee(()) method will ccrrooaakk(()) if it fails reading data for some
reason. If it croaks it is unpredictable what the state of the $ctx
object will be in. The aaddddffiillee(()) method might have been able to read
the file partially before it failed. It is probably wise to discard
or reset the $ctx object if this occurs.
In most cases you want to make sure that the $io_handle is in
"binmode" before you pass it as argument to the aaddddffiillee(()) method.
$ctx->add_bits( $data, $nbits )
$ctx->add_bits( $bitstring )
The aadddd__bbiittss(()) method is an alternative to aadddd(()) that allow partial
bytes to be appended to the message. Most users can just ignore this
method since typical applications involve only whole-byte data.
The two argument form of aadddd__bbiittss(()) 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)".
The one argument form of aadddd__bbiittss(()) takes a $bitstring of "1" and "0"
chars as argument. It's a shorthand for "$ctx->add_bits(pack("B*",
$bitstring), length($bitstring))".
The return value is the $ctx object itself.
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 and for these it is not
possible to add bits that are not a multiple of 8, and the aadddd__bbiittss(())
method will croak if 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" and can be used to calculate another digest
value. Call $ctx->clone->digest if you want to calculate the digest
without resetting the digest state.
$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 without padding.
$ctx->base64_padded_digest
Same as $ctx->digest, but will return the digest as a base64 encoded
string.
DDiiggeesstt ssppeeeedd This table should give some indication on the relative speed of different 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.
SSEEEE AALLSSOO #
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
http://en.wikipedia.org/wiki/Cryptographic_hash_function
AAUUTTHHOORR #
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 1998-2006 Gisle Aas.
Copyright 1995,1996 Neil Winton.
perl v5.36.3 2023-02-15 Digest(3p)