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dpavlin |
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#!/usr/bin/perl -w |
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# guess-crc.pl |
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# |
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# 09/28/08 21:54:24 CEST Dobrica Pavlinusic <dpavlin@rot13.org> |
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dpavlin |
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# CRC info from: http://stackoverflow.com/questions/149617/how-could-i-guess-a-checksum-algorithm |
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# and from: http://www.geocities.com/SiliconValley/Pines/8659/crc.htm |
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# LRC: Polynomial=0x81; 8 bits; Normal; Initial=0; Final=as calculated |
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# CRC16: Polynomial=0xa001; 16 bits; Normal; Initial=0; Final=as calculated |
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# CCITT: Polynomial=0x1021; 16 bits; reverse; Initial=0xffff; Final=0x1d0f |
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# Xmodem: Polynomial=0x1021; 16 bits; reverse; Initial=0; Final=0x1d0f |
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# CRC32: Polynomial=0xebd88320; 32 bits; Normal; Initial=0xffffffff; Final=inverted value |
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# ZIP32: Polynomial=0x04c11db7; 32 bits; Normal; Initial=0xffffffff; Final=as calculated |
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# IPX: Polynomial=0x8005; 16 bits; Reverse; Initial=0xffff; Final=as calculated |
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# ISO 18000-6B: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated |
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# ISO 18000-6C: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated |
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# Data must be padded with zeroes to make a multiple of 8 bits |
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# ISO CRC5: Polynomial=custom; 5 bits; Reverse; Initial=0x9; Final=shifted left by 3 bits |
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# Data must be padded with zeroes to make a multiple of 8 bits |
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# EPC class 1: Polynomial=custom 0x1021; 16 bits; Reverse; Initial=0xffff; Final=post processing of 16 zero bits |
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dpavlin |
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use strict; |
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use Digest::CRC qw(crc32 crc16 crcccitt crc crc8); |
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use Data::Dump qw/dump/; |
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dpavlin |
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use File::Slurp; |
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dpavlin |
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dpavlin |
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my $debug = 1 if @ARGV; |
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dpavlin |
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sub hex2b { |
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my $hex = shift; |
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return map { hex($_) } split(/\s+/, $hex); |
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} |
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dpavlin |
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my @check_polys = ( 0x0000 .. 0xffff ); |
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dpavlin |
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#@check_polys = ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 ); # crc16 |
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@check_polys = ( 31125, 53345, 11642, 24337, 51699, 55122, 15257 ); # ccitt |
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dpavlin |
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dpavlin |
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my @check_offset = ( 0,1,2,3 ); |
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@check_offset = ( 1 ); # skip first, second always zero |
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dpavlin |
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my @try_polys = ( |
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{ name => "CRC-16/CITT", width => 16, poly => 0x1021, init => 0xFFFF, refin => 0, refout => 0, xorout => 0x0000 }, |
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{ name => "XMODEM", width => 16, poly => 0x8408, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 }, |
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{ name => "ARC", width => 16, poly => 0x8005, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 }, |
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{ name => "CRC-16", width => 16, poly => 0xA001, init => 0x0000, refin => 0, refout => 0, xorout => 0x0000 }, |
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); |
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my @data = ( |
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'D5 00 05 04 00 11 8C 66', |
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'D6 00 05 FE 00 05 FA 40', |
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); |
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#@data = read_file('all.out') if -e 'all.out'; |
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dpavlin |
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my $found_polys; |
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sub check_crc { |
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my ( $poly, $bytes, $wanted ) = @_; |
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my $ctx = Digest::CRC->new( |
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#width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>0x1021, refin=>0 # ccitt |
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#width=>16, init=>0, xorout=>0, refout=>1, poly=>0x8005, refin=>1 # crc16 |
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#0x8408, |
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#0xa001, |
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dpavlin |
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#width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1 # crc16 |
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width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>$poly, refin=>0 # ccitt |
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dpavlin |
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); |
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$ctx->add( $bytes ); |
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my $try = $ctx->digest; |
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dpavlin |
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my $n = pack('n*', $try); |
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my $v = pack('n*', $try); |
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warn "## check_crc( $poly, ",dump($bytes)," ) = ",dump( $n, $v, $wanted ) if $debug; |
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return $n eq $wanted || $v eq $wanted; |
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dpavlin |
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} |
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dpavlin |
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foreach ( @data ) { |
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dpavlin |
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my $hex = $_; |
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$hex =~ s/\s+//g; |
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my $bytes = pack('H*', substr($hex, 0, -4)); |
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dpavlin |
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print "?? guess crc ",substr($hex,-4),"\n"; |
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dpavlin |
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my $crc = pack('H4', substr($hex,-4)); |
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warn "input $_ => ",dump( $bytes, $crc ) if $debug; |
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dpavlin |
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dpavlin |
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foreach my $o ( @check_offset ) { |
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dpavlin |
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my $b = substr( $bytes, $o ); |
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dpavlin |
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foreach my $poly ( @check_polys ) { |
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dpavlin |
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print "## poly $poly\n" if $poly % 1000 == 0; |
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dpavlin |
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if ( check_crc( $poly, $b, $crc ) ) { |
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warn "HIT: $o poly: $poly\n"; |
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$found_polys->{$poly}->{$o}++; |
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dpavlin |
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} |
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} |
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} |
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} |
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dpavlin |
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print "FOUND polys = ", dump( $found_polys ); |
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