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Digest::SHA(3perl) Perl Programmers Reference Guide Digest::SHA(3perl)
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; # make copy of digest object
$state = $sha->getstate; # save current state to string
$sha->putstate($state); # restore previous $state
$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, SHA-512,
SHA-512/224, and SHA-512/256 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 a string. The getstate() method
generates portable, human-readable text describing the current state of computation. You
can subsequently restore that state with putstate() to resume where the calculation left
off.
To see what a state description looks like, just run the following:
use Digest::SHA;
print Digest::SHA->new->add("Shaw" x 1962)->getstate;
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";
UNICODE AND SIDE EFFECTS
Perl supports Unicode strings as of version 5.6. Such strings may contain wide
characters, namely, characters whose ordinal values are greater than 255. This can cause
problems for digest algorithms such as SHA that are specified to operate on sequences of
bytes.
The rule by which Digest::SHA handles a Unicode string is easy to state, but potentially
confusing to grasp: the string is interpreted as a sequence of byte values, where each
byte value is equal to the ordinal value (viz. code point) of its corresponding Unicode
character. That way, the Unicode string 'abc' has exactly the same digest value as the
ordinary string 'abc'.
Since a wide character does not fit into a byte, the Digest::SHA routines croak if they
encounter one. Whereas if a Unicode string contains no wide characters, the module
accepts it quite happily. The following code illustrates the two cases:
$str1 = pack('U*', (0..255));
print sha1_hex($str1); # ok
$str2 = pack('U*', (0..256));
print sha1_hex($str2); # croaks
Be aware that the digest routines silently convert UTF-8 input into its equivalent byte
sequence in the native encoding (cf. utf8::downgrade). This side effect influences only
the way Perl stores the data internally, but otherwise leaves the actual value of the data
intact.
NIST STATEMENT ON SHA-1
NIST acknowledges that the work of Prof. Xiaoyun Wang constitutes a practical collision
attack on SHA-1. Therefore, NIST encourages the rapid adoption of the SHA-2 hash
functions (e.g. SHA-256) for applications requiring strong collision resistance, such as
digital signatures.
ref. <http://csrc.nist.gov/groups/ST/hash/statement.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, ...)
sha512224($data, ...)
sha512256($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($data, ...)
sha512224_hex($data, ...)
sha512256_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, ...)
sha512224_base64($data, ...)
sha512256_base64($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, 512,
512224, or 512256. 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 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($alg). In fact, reset is just an alias
for new.
hashsize
Returns the number of digest bits for this object. The values are 160, 224, 256, 384,
512, 224, and 256 for SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224 and
SHA-512/256, respectively.
algorithm
Returns the digest algorithm for this object. The values are 1, 224, 256, 384, 512,
512224, and 512256 for SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and
SHA-512/256, respectively.
clone
Returns a duplicate copy of the object.
add($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);
Note that SHA-1 and SHA-2 use most-significant-bit ordering for their internal state.
This means that
$sha3->add_bits("110");
is equivalent to
$sha3->add_bits("1")->add_bits("1")->add_bits("0");
addfile(*FILE)
Reads from FILE until EOF, and appends that data to the current state. The return
value is the updated object itself.
addfile($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
"U" use universal newlines
"0" use BITS mode
The "U" mode is modeled on Python's "Universal Newlines" concept, whereby DOS and Mac
OS line terminators are converted internally to UNIX newlines before processing. This
ensures consistent digest values when working simultaneously across multiple file
systems. The "U" mode influences only text files, namely those passing Perl's -T
test; binary files are processed with no translation whatsoever.
The BITS mode ("0") interprets the contents of $filename as a logical stream of bits,
where each ASCII '0' or '1' character represents a 0 or 1 bit, respectively. All
other characters are ignored. This provides a convenient way to calculate the digest
values of partial-byte data by using files, rather than having to write separate
programs employing the add_bits method.
getstate
Returns a string containing a portable, human-readable representation of the current
SHA state.
putstate($str)
Returns a Digest::SHA object representing the SHA state contained in $str. The format
of $str matches the format of the output produced by method getstate. 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 $str.
dump($filename)
Writes the output of getstate 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 that results from calling putstate on the contents of
$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.
b64digest
Returns the digest encoded as a Base64 string.
Like digest, this method is a read-once operation. Call $sha->clone->b64digest if
it's necessary to preserve the original digest state.
It's important to note that the resulting string does not contain the padding
characters typical of Base64 encodings. This omission is deliberate, and is done to
maintain compatibility with the family of CPAN Digest modules. See "PADDING OF BASE64
DIGESTS" for details.
HMAC-SHA-1/224/256/384/512
hmac_sha1($data, $key)
hmac_sha224($data, $key)
hmac_sha256($data, $key)
hmac_sha384($data, $key)
hmac_sha512($data, $key)
hmac_sha512224($data, $key)
hmac_sha512256($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, $key)
hmac_sha512224_hex($data, $key)
hmac_sha512256_hex($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, $key)
hmac_sha512224_base64($data, $key)
hmac_sha512256_base64($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 (Draft FIPS PUB 180-4) can be found at:
<http://csrc.nist.gov/publications/drafts/fips180-4/Draft-FIPS180-4_Feb2011.pdf>
The Keyed-Hash Message Authentication Code (HMAC):
<http://csrc.nist.gov/publications/fips/fips198/fips-198a.pdf>
AUTHOR
Mark Shelor <mshelor AT cpan.org>
ACKNOWLEDGMENTS
The author is particularly grateful to
Gisle Aas
H. Merijn Brand
Sean Burke
Chris Carey
Alexandr Ciornii
Chris David
Jim Doble
Thomas Drugeon
Julius Duque
Jeffrey Friedl
Robert Gilmour
Brian Gladman
Jarkko Hietaniemi
Adam Kennedy
Mark Lawrence
Andy Lester
Alex Muntada
Steve Peters
Chris Skiscim
Martin Thurn
Gunnar Wolf
Adam Woodbury
"who by trained skill rescued life from such great billows and such thick darkness and
moored it in so perfect a calm and in so brilliant a light" - Lucretius
COPYRIGHT AND LICENSE
Copyright (C) 2003-2018 Mark Shelor
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
perlartistic
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