difficult to show a small sample really.. on further investigation it seems unpack is really not doing what I'd expect it to: the message substr: 637573746F6D65726E616D6528BF4E5E4E758A4164004E56FFFA01082E2E00B6 is correctly unchanged all the way until we unpack it: 
    my $ms = $ml < $MAX_CHUNK_SIZE ? $ml : $MAX_CHUNK_SIZE;
    for my $piece ( 0..$num_pieces - 1 ) {
      my $ss = substr($message, $piece * $MAX_CHUNK_SIZE, $ms); # fine
+ up to here...
      my $ssl = length $ss;
      my @message = unpack( "C*", $ss ); ### at this point the charact
+ers are changed... we go from 32 to 37 characters (in the array). why
+?
    # i've changed the code in the RC4 package here slightly to allow 
+testing. 
    # it produces identical results in all cases considered here.

[download]
then it becomes (pack'ing it again and converting to hex for display):
637573746F6D65726E616D6528C2BF4E5E4E75C28A4164004E56C3BFC3BA01082E2E00C2B6
looking at these 2 strings you can see some characters are being inserted:
637573746F6D65726E616D6528 BF4E5E4E75 8A4164004E56 FFF A0108 2E2E00B6 #correct
637573746F6D65726E616D6528 C2 BF4E5E4E75 C2 8A4164004E56 C3BFC3B A0108 2E2E00 C2 B6 #faulty

so unpack is somehow inserting those C2 (Â in ascii) characters and changing the FFF (12 bits) to C3BFC3B

what could be making unpack behave in this way?

In reply to Re^2: perplexing inconsistency using RC4 and unpack by oddmedley
in thread perplexing inconsistency using RC4 and unpack by oddmedley

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