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#!/usr/bin/perl -s
##
## Crypt::RSA::DataFormat -- Functions for converting, shaping and
## creating and reporting data formats.
##
## Copyright (c) 2001, Vipul Ved Prakash. All rights reserved.
## This code is free software; you can redistribute it and/or modify
## it under the same terms as Perl itself.
##
## $Id: DataFormat.pm,v 1.13 2001/05/20 23:37:45 vipul Exp $
package Crypt::RSA::DataFormat;
use vars qw(@ISA);
use Math::Pari qw(PARI pari2pv floor pari2num);
use Crypt::Random qw(makerandom);
use Digest::SHA1 qw(sha1);
use Carp;
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw(i2osp os2ip h2osp octet_xor octet_len bitsize
generate_random_octet mgf1 steak);
sub i2osp {
my $num = PARI(shift);
my $d = $num;
my $l = shift || 0;
my $base = PARI(256); my $result = '';
if ($l) { return if $num > $base ** $l }
do {
my $r = $d % $base;
$d = ($d-$r) / $base;
$result = chr($r) . $result;
} until ($d < $base);
$result = chr($d) . $result if $d != 0;
if (length($result) < $l) {
$result = chr(0)x($l-length($result)) . $result;
}
return $result;
}
sub os2ip {
my $string = shift;
my $base = PARI(256);
my $result = 0;
my $l = length($string);
for (0 .. $l-1) {
my ($c) = unpack "x$_ a", $string;
my $a = int(ord($c));
my $val = int($l-$_-1);
$result += $a * ($base**$val);
}
return $result;
}
sub h2osp {
my $hex = shift;
$hex =~ s/[ \n]//ig;
my $num = Math::Pari::_hex_cvt($hex);
return i2osp ($num);
}
sub generate_random_octet {
my ( $l, $str ) = @_;
my $r = makerandom ( Size => int($l*8), Strength => $str );
return i2osp ($r, $l);
}
sub bitsize ($) {
return pari2num(floor(Math::Pari::log(shift)/Math::Pari::log(2)) + 1);
}
sub octet_len {
return pari2num(floor(PARI((bitsize(shift)+7)/8)));
}
sub octet_xor {
my ($a, $b) = @_; my @xor;
my @ba = split //, unpack "B*", $a;
my @bb = split //, unpack "B*", $b;
if (@ba != @bb) {
if (@ba < @bb) {
for (1..@bb-@ba) { unshift @ba, '0' }
} else {
for (1..@ba-@bb) { unshift @bb, '0' }
}
}
for (0..$#ba) {
$xor[$_] = ($ba[$_] xor $bb[$_]) || 0;
}
return pack "B*", join '',@xor;
}
sub mgf1 {
my ($seed, $l) = @_;
my $hlen = 20; my ($T, $i) = ("",0);
while ($i <= $l) {
my $C = i2osp (int($i), 4);
$T .= sha1("$seed$C");
$i += $hlen;
}
my ($output) = unpack "a$l", $T;
return $output;
}
sub steak {
my ($text, $blocksize) = @_;
my $textsize = length($text);
my $chunkcount = $textsize % $blocksize
? int($textsize/$blocksize) + 1 : $textsize/$blocksize;
my @segments = unpack "a$blocksize"x$chunkcount, $text;
return @segments;
}
1;
=head1 NAME
Crypt::RSA::DataFormat - Data creation, conversion and reporting primitives.
=head1 DESCRIPTION
This module implements several data creation, conversion and reporting
primitives used throughout the Crypt::RSA implementation. Primitives are
available as exportable functions.
=head1 FUNCTIONS
=over 4
=item B<i2osp> Integer, Length
Integer To Octet String Primitive. Converts an integer into its
equivalent octet string representation of length B<Length>. If
necessary, the resulting string is prefixed with nulls. If
B<Length> is not provided, returns an octet string of shortest
possible length.
=item B<h2osp> Hex String
Hex To Octet String Primitive. Converts a I<hex string> into its
equivalent octet string representation and returns an octet
string of shortest possible length. The hex string is not
prefixed with C<0x>, etc.
=item B<os2ip> String
Octet String to Integer Primitive. Converts an octet string into its
equivalent integer representation.
=item B<generate_random_octet> Length, Strength
Generates a random octet string of length B<Length>. B<Strength> specifies
the degree of randomness. See Crypt::Random(3) for an explanation of the
B<Strength> parameter.
=item B<bitsize> Integer
Returns the length of the B<Integer> in bits.
=item B<octet_len> Integer
Returns the octet length of the integer. If the length is not a whole
number, the fractional part is dropped to make it whole.
=item B<octet_xor> String1, String2
Returns the result of B<String1> XOR B<String2>.
=item B<steak> String, Length
Returns an array of segments of length B<Length> from B<String>. The final
segment can be smaller than B<Length>.
=back
=head1 AUTHOR
Vipul Ved Prakash, E<lt>mail@vipul.netE<gt>
=cut
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