Bug#648546: add OpenPGP ASCII armor checksum to Digest::CRC

[Daniel Kahn Gillmor]

Package: libdigest-crc-perl
Version: 0.17-1
Severity: wishlist
Tags: patch upstream

One common CRC used on the 'net today is the radix-64 armor checksum
specified in the OpenPGP standard:

 https://tools.ietf.org/html/rfc4880#section-6

This is already possible to implement with Digest::CRC using the
following object:

my $ctx = Digest::CRC->new(width => 24, init=> 0xB704CE,
                           xorout => 0x000000, refout => 0,
                           poly => 0x864CFB, refin => 0,
                           cont => 1);

But this is kind of bulky and inconvenient to use.

The attached patch enhances Digest::CRC by adding a crcopenpgparmor
type, and exporting a function of the same name.  It should apply to
version 0.17 of Digest::CRC.

I'd be happy to have this patch included upstream, and release it under
the same terms as the upstream source.

Thanks for Digest::CRC, it's very much appreciated.

Regards,

        --dkg


--- lib/Digest/CRC.pm	2011-11-12 14:47:51.000000000 -0500
+++ /usr/lib/perl5/Digest/CRC.pm	2011-11-12 14:32:31.000000000 -0500
@@ -8,11 +8,12 @@
 @ISA = qw(Exporter);
 
 @EXPORT_OK = qw(
- crc8 crcccitt crc16 crc32 crc64 crc
+ crc8 crcccitt crc16 crcopenpgparmor crc32 crc64 crc
  crc_hex crc_base64
  crcccitt_hex crcccitt_base64
  crc8_hex crc8_base64
  crc16_hex crc16_base64
+ crcopenpgparmor_hex crcopenpgparmor_base64
  crc32_hex crc32_base64
  crc64_hex crc64_base64
 );
@@ -126,6 +127,7 @@
   crc8 => [8,0,0,0,0x07,0,0],
   crcccitt => [16,0xffff,0,0,0x1021,0,0],
   crc16 => [16,0,0,1,0x8005,1,0],
+  crcopenpgparmor => [24,0xB704CE,0,0,0x864CFB,0,0],
   crc32 => [32,0xffffffff,0xffffffff,1,0x04C11DB7,1,0],
 );
 
@@ -273,6 +275,12 @@
 
 sub crc16 { crc($_[0],@{$_typedef{crc16}}) }
 
+# CRC-24 for OpenPGP ASCII Armor checksum
+# https://tools.ietf.org/html/rfc4880#section-6
+# poly: 0x864CFB, width: 24, init: 0xB704CE, refin: no, refout: no, xorout: no
+
+sub crcopenpgparmor { crc($_[0],@{$_typedef{crcopenpgparmor}}) }
+
 # CRC32
 # poly: 04C11DB7, width: 32, init: FFFFFFFF, revin: yes, revout: yes,
 # xorout: FFFFFFFF
@@ -301,6 +309,10 @@
 
 sub crc16_base64 { _encode_base64 &crc16 }
 
+sub crcopenpgparmor_hex { _encode_hex &crcopenpgparmor }
+
+sub crcopenpgparmor_base64 { _encode_base64 &crcopenpgparmor }
+
 sub crc32_hex { _encode_hex &crc32 }
 
 sub crc32_base64 { _encode_base64 &crc32 }
@@ -320,12 +332,13 @@
 
   # Functional style
 
-  use Digest::CRC qw(crc64 crc32 crc16 crcccitt crc crc8);
+  use Digest::CRC qw(crc64 crc32 crc16 crcccitt crc crc8 crcopenpgparmor);
   $crc = crc64("123456789");
   $crc = crc32("123456789");
   $crc = crc16("123456789");
   $crc = crcccitt("123456789");
   $crc = crc8("123456789");
+  $crc = crcopenpgparmor("123456789");
 
   $crc = crc($input,$width,$init,$xorout,$refout,$poly,$refin,$cont);
 
@@ -348,7 +361,12 @@
 
 The B<Digest::CRC> module calculates CRC sums of all sorts.
 It contains wrapper functions with the correct parameters for CRC-CCITT,
-CRC-16, CRC-32 and CRC-64.
+CRC-16, CRC-32 and CRC-64, as well as the CRC used in OpenPGP's
+ASCII-armored checksum.
+
+=head1 SEE ALSO
+
+https://tools.ietf.org/html/rfc4880#section-6
 
 =head1 AUTHOR
 

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