BrowserUk,

...ASCII or ISO text, certain parts of the input range -- many of the control characters <32; and characters >126 -- will not appear...

I hadn't thought about it but since the files were encrypted, more character sequences might appear.

As far as the 'SimCRC64' algorithm, it was just a simple CRC routine. I don't have the actual code, but it was something like this.

 my $crc = crc64(\$output);           ## Add crc check to output data

 sub crc64           ## Add crc check to output data
 {   my $data = shift; my $crc = ""; my $len = length($$data); my $pos
+ = 0;
     while ( $pos < $len )
     {  $crc = $crc ^ ( substr($$data,$pos,8) );
        $pos += 8;
     }
     return ( $crc );
 }
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It was part of the test to see what the worst case would be. As I previously said, I didn't expect the results.

Thank you