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Digest::SHA(3pm) Perl Programmers Reference Guide Digest::SHA(3pm)
NAME
Digest::SHA - Perl extension for SHA-1/224/256/384/512
SYNOPSIS
In programs:
# Functional interface
use Digest::SHA qw(sha1 sha1_hex sha1_base64 ...);
$digest = sha1($data);
$digest = sha1_hex($data);
$digest = sha1_base64($data);
$digest = sha256($data);
$digest = sha384_hex($data);
$digest = sha512_base64($data);
# Object-oriented
use Digest::SHA;
$sha = Digest::SHA->new($alg);
$sha->add($data); # feed data into stream
$sha->addfile(*F);
$sha->addfile($filename);
$sha->add_bits($bits);
$sha->add_bits($data, $nbits);
$sha_copy = $sha->clone; # if needed, make copy of
$sha->dump($file); # current digest state,
$sha->load($file); # or save it on disk
$digest = $sha->digest; # compute digest
$digest = $sha->hexdigest;
$digest = $sha->b64digest;
From the command line:
$ shasum files
$ shasum --help
SYNOPSIS (HMAC-SHA)
# Functional interface only
use Digest::SHA qw(hmac_sha1 hmac_sha1_hex ...);
$digest = hmac_sha1($data, $key);
$digest = hmac_sha224_hex($data, $key);
$digest = hmac_sha256_base64($data, $key);
ABSTRACT
Digest::SHA is a complete implementation of the NIST Secure Hash Standard. It gives Perl programmers a convenient way to
calculate SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512 message digests. The module can handle all types of input,
including partial-byte data.
DESCRIPTION
Digest::SHA is written in C for speed. If your platform lacks a C compiler, you can install the functionally equivalent
(but much slower) Digest::SHA::PurePerl module.
The programming interface is easy to use: it's the same one found in CPAN's Digest module. So, if your applications
currently use Digest::MD5 and you'd prefer the stronger security of SHA, it's a simple matter to convert them.
The interface provides two ways to calculate digests: all-at-once, or in stages. To illustrate, the following short
program computes the SHA-256 digest of "hello world" using each approach:
use Digest::SHA qw(sha256_hex);
$data = "hello world";
@frags = split(//, $data);
# all-at-once (Functional style)
$digest1 = sha256_hex($data);
# in-stages (OOP style)
$state = Digest::SHA->new(256);
for (@frags) { $state->add($_) }
$digest2 = $state->hexdigest;
print $digest1 eq $digest2 ?
"whew!\n" : "oops!\n";
To calculate the digest of an n-bit message where n is not a multiple of 8, use the add_bits() method. For example,
consider the 446-bit message consisting of the bit-string "110" repeated 148 times, followed by "11". Here's how to
display its SHA-1 digest:
use Digest::SHA;
$bits = "110" x 148 . "11";
$sha = Digest::SHA->new(1)->add_bits($bits);
print $sha->hexdigest, "\n";
Note that for larger bit-strings, it's more efficient to use the two-argument version add_bits($data, $nbits), where
$data is in the customary packed binary format used for Perl strings.
The module also lets you save intermediate SHA states to disk, or display them on standard output. The dump() method
generates portable, human-readable text describing the current state of computation. You can subsequently retrieve the
file with load() to resume where the calculation left off.
To see what a state description looks like, just run the following:
use Digest::SHA;
Digest::SHA->new->add("Shaw" x 1962)->dump;
As an added convenience, the Digest::SHA module offers routines to calculate keyed hashes using the
HMAC-SHA-1/224/256/384/512 algorithms. These services exist in functional form only, and mimic the style and behavior of
the sha(), sha_hex(), and sha_base64() functions.
# Test vector from draft-ietf-ipsec-ciph-sha-256-01.txt
use Digest::SHA qw(hmac_sha256_hex);
print hmac_sha256_hex("Hi There", chr(0x0b) x 32), "\n";
NIST STATEMENT ON SHA-1
NIST was recently informed that researchers had discovered a way to "break" the current Federal Information Processing
Standard SHA-1 algorithm, which has been in effect since 1994. The researchers have not yet published their complete
results, so NIST has not confirmed these findings. However, the researchers are a reputable research team with expertise
in this area.
Due to advances in computing power, NIST already planned to phase out SHA-1 in favor of the larger and stronger hash
functions (SHA-224, SHA-256, SHA-384 and SHA-512) by 2010. New developments should use the larger and stronger hash
functions.
ref. <http://www.csrc.nist.gov/pki/HashWorkshop/NIST%20Statement/Burr_Mar2005.html>
PADDING OF BASE64 DIGESTS
By convention, CPAN Digest modules do not pad their Base64 output. Problems can occur when feeding such digests to other
software that expects properly padded Base64 encodings.
For the time being, any necessary padding must be done by the user. Fortunately, this is a simple operation: if the
length of a Base64-encoded digest isn't a multiple of 4, simply append "=" characters to the end of the digest until it
is:
while (length($b64_digest) % 4) {
$b64_digest .= '=';
}
To illustrate, sha256_base64("abc") is computed to be
ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0
which has a length of 43. So, the properly padded version is
ungWv48Bz+pBQUDeXa4iI7ADYaOWF3qctBD/YfIAFa0=
EXPORT
None by default.
EXPORTABLE FUNCTIONS
Provided your C compiler supports a 64-bit type (e.g. the long long of C99, or __int64 used by Microsoft C/C++), all of
these functions will be available for use. Otherwise, you won't be able to perform the SHA-384 and SHA-512 transforms,
both of which require 64-bit operations.
Functional style
sha1($data, ...)
sha224($data, ...)
sha256($data, ...)
sha384($data, ...)
sha512($data, ...)
Logically joins the arguments into a single string, and returns its SHA-1/224/256/384/512 digest encoded as a binary
string.
sha1_hex($data, ...)
sha224_hex($data, ...)
sha256_hex($data, ...)
sha384_hex($data, ...)
sha512_hex($data, ...)
Logically joins the arguments into a single string, and returns its SHA-1/224/256/384/512 digest encoded as a
hexadecimal string.
sha1_base64($data, ...)
sha224_base64($data, ...)
sha256_base64($data, ...)
sha384_base64($data, ...)
sha512_base64($data, ...)
Logically joins the arguments into a single string, and returns its SHA-1/224/256/384/512 digest encoded as a Base64
string.
It's important to note that the resulting string does not contain the padding characters typical of Base64 encodings.
This omission is deliberate, and is done to maintain compatibility with the family of CPAN Digest modules. See
"PADDING OF BASE64 DIGESTS" for details.
OOP style
new($alg)
Returns a new Digest::SHA object. Allowed values for $alg are 1, 224, 256, 384, or 512. It's also possible to use
common string representations of the algorithm (e.g. "sha256", "SHA-384"). If the argument is missing, SHA-1 will be
used by default.
Invoking new as an instance method will not create a new object; instead, it will simply reset the object to the
initial state associated with $alg. If the argument is missing, the object will continue using the same algorithm
that was selected at creation.
reset($alg)
This method has exactly the same effect as new($alg). In fact, reset is just an alias for new.
hashsize
Returns the number of digest bits for this object. The values are 160, 224, 256, 384, and 512 for SHA-1, SHA-224,
SHA-256, SHA-384, and SHA-512, respectively.
algorithm
Returns the digest algorithm for this object. The values are 1, 224, 256, 384, and 512 for SHA-1, SHA-224, SHA-256,
SHA-384, and SHA-512, respectively.
clone
Returns a duplicate copy of the object.
add($data, ...)
Logically joins the arguments into a single string, and uses it to update the current digest state. In other words,
the following statements have the same effect:
$sha->add("a"); $sha->add("b"); $sha->add("c");
$sha->add("a")->add("b")->add("c");
$sha->add("a", "b", "c");
$sha->add("abc");
The return value is the updated object itself.
add_bits($data, $nbits)
add_bits($bits)
Updates the current digest state by appending bits to it. The return value is the updated object itself.
The first form causes the most-significant $nbits of $data to be appended to the stream. The $data argument is in
the customary binary format used for Perl strings.
The second form takes an ASCII string of "0" and "1" characters as its argument. It's equivalent to
$sha->add_bits(pack("B*", $bits), length($bits));
So, the following two statements do the same thing:
$sha->add_bits("111100001010");
$sha->add_bits("\xF0\xA0", 12);
addfile(*FILE)
Reads from FILE until EOF, and appends that data to the current state. The return value is the updated object
itself.
addfile($filename [, $mode])
Reads the contents of $filename, and appends that data to the current state. The return value is the updated object
itself.
By default, $filename is simply opened and read; no special modes or I/O disciplines are used. To change this, set
the optional $mode argument to one of the following values:
"b" read file in binary mode
"p" use portable mode
The "p" mode is handy since it ensures that the digest value of $filename will be the same when computed on different
operating systems. It accomplishes this by internally translating all newlines in text files to UNIX format before
calculating the digest. Binary files are read in raw mode with no translation whatsoever.
For a fuller discussion of newline formats, refer to CPAN module File::LocalizeNewlines. Its "universal line
separator" regex forms the basis of addfile's portable mode processing.
dump($filename)
Provides persistent storage of intermediate SHA states by writing a portable, human-readable representation of the
current state to $filename. If the argument is missing, or equal to the empty string, the state information will be
written to STDOUT.
load($filename)
Returns a Digest::SHA object representing the intermediate SHA state that was previously dumped to $filename. If
called as a class method, a new object is created; if called as an instance method, the object is reset to the state
contained in $filename. If the argument is missing, or equal to the empty string, the state information will be read
from STDIN.
digest
Returns the digest encoded as a binary string.
Note that the digest method is a read-once operation. Once it has been performed, the Digest::SHA object is
automatically reset in preparation for calculating another digest value. Call $sha->clone->digest if it's necessary
to preserve the original digest state.
hexdigest
Returns the digest encoded as a hexadecimal string.
Like digest, this method is a read-once operation. Call $sha->clone->hexdigest if it's necessary to preserve the
original digest state.
This method is inherited if Digest::base is installed on your system. Otherwise, a functionally equivalent
substitute is used.
b64digest
Returns the digest encoded as a Base64 string.
Like digest, this method is a read-once operation. Call $sha->clone->b64digest if it's necessary to preserve the
original digest state.
This method is inherited if Digest::base is installed on your system. Otherwise, a functionally equivalent
substitute is used.
It's important to note that the resulting string does not contain the padding characters typical of Base64 encodings.
This omission is deliberate, and is done to maintain compatibility with the family of CPAN Digest modules. See
"PADDING OF BASE64 DIGESTS" for details.
HMAC-SHA-1/224/256/384/512
hmac_sha1($data, $key)
hmac_sha224($data, $key)
hmac_sha256($data, $key)
hmac_sha384($data, $key)
hmac_sha512($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with the result encoded as a binary string. Multiple
$data arguments are allowed, provided that $key is the last argument in the list.
hmac_sha1_hex($data, $key)
hmac_sha224_hex($data, $key)
hmac_sha256_hex($data, $key)
hmac_sha384_hex($data, $key)
hmac_sha512_hex($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with the result encoded as a hexadecimal string.
Multiple $data arguments are allowed, provided that $key is the last argument in the list.
hmac_sha1_base64($data, $key)
hmac_sha224_base64($data, $key)
hmac_sha256_base64($data, $key)
hmac_sha384_base64($data, $key)
hmac_sha512_base64($data, $key)
Returns the HMAC-SHA-1/224/256/384/512 digest of $data/$key, with the result encoded as a Base64 string. Multiple
$data arguments are allowed, provided that $key is the last argument in the list.
It's important to note that the resulting string does not contain the padding characters typical of Base64 encodings.
This omission is deliberate, and is done to maintain compatibility with the family of CPAN Digest modules. See
"PADDING OF BASE64 DIGESTS" for details.
SEE ALSO
Digest, Digest::SHA::PurePerl
The Secure Hash Standard (FIPS PUB 180-2) can be found at:
http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
<http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf>;
The Keyed-Hash Message Authentication Code (HMAC):
http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf
<http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf>;
AUTHOR
Mark Shelor <mshelorATcpan.org>
ACKNOWLEDGMENTS
The author is particularly grateful to
Gisle Aas
Chris Carey
Alexandr Ciornii
Jim Doble
Julius Duque
Jeffrey Friedl
Robert Gilmour
Brian Gladman
Adam Kennedy
Andy Lester
Alex Muntada
Steve Peters
Chris Skiscim
Martin Thurn
Gunnar Wolf
Adam Woodbury
for their valuable comments and suggestions.
COPYRIGHT AND LICENSE
Copyright (C) 2003-2008 Mark Shelor
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perlartistic
perl v5.12.4 2011-06-07 Digest::SHA(3pm)
