/[RFID]/guess-crc.pl
This is repository of my old source code which isn't updated any more. Go to git.rot13.org for current projects!
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Contents of /guess-crc.pl

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Revision 13 - (show annotations)
Wed Oct 1 18:45:35 2008 UTC (14 years, 2 months ago) by dpavlin
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1 #!/usr/bin/perl -w
2
3 # guess-crc.pl
4 #
5 # 09/28/08 21:54:24 CEST Dobrica Pavlinusic <dpavlin@rot13.org>
6
7 # CRC info from: http://stackoverflow.com/questions/149617/how-could-i-guess-a-checksum-algorithm
8 # and from: http://www.geocities.com/SiliconValley/Pines/8659/crc.htm
9
10 # LRC: Polynomial=0x81; 8 bits; Normal; Initial=0; Final=as calculated
11 # CRC16: Polynomial=0xa001; 16 bits; Normal; Initial=0; Final=as calculated
12 # CCITT: Polynomial=0x1021; 16 bits; reverse; Initial=0xffff; Final=0x1d0f
13 # Xmodem: Polynomial=0x1021; 16 bits; reverse; Initial=0; Final=0x1d0f
14 # CRC32: Polynomial=0xebd88320; 32 bits; Normal; Initial=0xffffffff; Final=inverted value
15 # ZIP32: Polynomial=0x04c11db7; 32 bits; Normal; Initial=0xffffffff; Final=as calculated
16
17 # IPX: Polynomial=0x8005; 16 bits; Reverse; Initial=0xffff; Final=as calculated
18 # ISO 18000-6B: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated
19 # ISO 18000-6C: Polynomial=0x1021; 16 bits; Reverse; Initial=0xffff; Final=as calculated
20 # Data must be padded with zeroes to make a multiple of 8 bits
21 # ISO CRC5: Polynomial=custom; 5 bits; Reverse; Initial=0x9; Final=shifted left by 3 bits
22 # Data must be padded with zeroes to make a multiple of 8 bits
23 # EPC class 1: Polynomial=custom 0x1021; 16 bits; Reverse; Initial=0xffff; Final=post processing of 16 zero bits
24
25 use strict;
26
27 use Digest::CRC qw(crc32 crc16 crcccitt crc crc8);
28 use Data::Dump qw/dump/;
29 use File::Slurp;
30
31 my $debug = 1 if @ARGV;
32
33 sub hex2b {
34 my $hex = shift;
35 return map { hex($_) } split(/\s+/, $hex);
36 }
37
38 my @check_polys = ( 0x0000 .. 0xffff );
39 #@check_polys = ( 32833, 43271, 32833, 43271, 19299, 35925, 47123, 49319, 56971 ); # crc16
40 @check_polys = ( 31125, 53345, 11642, 24337, 51699, 55122, 15257 ); # ccitt
41
42 my @check_offset = ( 0,1,2,3 );
43 @check_offset = ( 1 ); # skip first, second always zero
44
45 my @try_polys = (
46 { name => "CRC-16/CITT", width => 16, poly => 0x1021, init => 0xFFFF, refin => 0, refout => 0, xorout => 0x0000 },
47 { name => "XMODEM", width => 16, poly => 0x8408, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 },
48 { name => "ARC", width => 16, poly => 0x8005, init => 0x0000, refin => 1, refout => 1, xorout => 0x0000 },
49 { name => "CRC-16", width => 16, poly => 0xA001, init => 0x0000, refin => 0, refout => 0, xorout => 0x0000 },
50 );
51
52 my @data = (
53 'D5 00 05 04 00 11 8C 66',
54 'D6 00 05 FE 00 05 FA 40',
55 );
56 #@data = read_file('all.out') if -e 'all.out';
57
58 my $found_polys;
59
60 sub check_crc {
61 my ( $poly, $bytes, $wanted ) = @_;
62 my $ctx = Digest::CRC->new(
63 #width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>0x1021, refin=>0 # ccitt
64 #width=>16, init=>0, xorout=>0, refout=>1, poly=>0x8005, refin=>1 # crc16
65 #0x8408,
66 #0xa001,
67 #width=>16, init=>0, xorout=>0, refout=>1, poly=>$poly,refin=>1 # crc16
68 width=>16, init=>0xffff, xorout=>0, refout=>1, poly=>$poly, refin=>0 # ccitt
69 );
70 $ctx->add( $bytes );
71 my $try = $ctx->digest;
72 my $n = pack('n*', $try);
73 my $v = pack('n*', $try);
74 warn "## check_crc( $poly, ",dump($bytes)," ) = ",dump( $n, $v, $wanted ) if $debug;
75 return $n eq $wanted || $v eq $wanted;
76 }
77
78 foreach ( @data ) {
79
80 my $hex = $_;
81 $hex =~ s/\s+//g;
82
83 my $bytes = pack('H*', substr($hex, 0, -4));
84
85 print "?? guess crc ",substr($hex,-4),"\n";
86 my $crc = pack('H4', substr($hex,-4));
87
88 warn "input $_ => ",dump( $bytes, $crc ) if $debug;
89
90 foreach my $o ( @check_offset ) {
91 my $b = substr( $bytes, $o );
92
93 foreach my $poly ( @check_polys ) {
94
95 print "## poly $poly\n" if $poly % 1000 == 0;
96
97 if ( check_crc( $poly, $b, $crc ) ) {
98 warn "HIT: $o poly: $poly\n";
99 $found_polys->{$poly}->{$o}++;
100 }
101 }
102 }
103 }
104
105 print "FOUND polys = ", dump( $found_polys );

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