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");
$sha->add_bits("\xF0\xA0", 12);
- addfile(*FILE)
- Reads from FILE until EOF, and appends that data to the current
state. The return value is the updated object itself.
- addfile($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
"p" use portable mode (to be deprecated)
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 "p" mode differs from "U" only in that it treats
"\r\r\n" as a single newline, a quirky feature designed to
accommodate legacy applications that occasionally added an extra carriage
return before DOS line terminators. The "p" mode will be phased
out eventually in favor of the cleaner and more well-established Universal
Newlines concept.
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@cpan.org>
ACKNOWLEDGMENTS¶
The author is particularly grateful to
Gisle Aas
H. Merijn Brand
Sean Burke
Chris Carey
Alexandr Ciornii
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) 2003-2014 Mark Shelor
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.
perlartistic