[118963] in Cypherpunks
Index of Coincidence Awk Program
daemon@ATHENA.MIT.EDU (trusted1@hushmail.com)
Mon Oct 11 13:48:53 1999
From: trusted1@hushmail.com
Message-Id: <199910111722.KAA11797@mail3.hushmail.com>
Date: Mon Oct 11 10:15:31 PDT 1999
To: cypherpunks@toad.com
Reply-To: trusted1@hushmail.com
# pipe in ciphertext.
# this computes index of coincidence to help determine key length.
# perl is better for larger quantities, but this would be fine for
# simple little XOR'd stuffs. 'total' is the actual number of
#coincidences per attempted shift.
#
# M1ckF0l3y
# Futile Crew
awk '{
s1=$0
for (shift=1;shift<=(length(s1)+1);shift++)
{
position=0
s2=(substr(s1,shift)(substr(s1,1,(shift-1))))
for (position=1;position<=(length(s1)+1);position++)
{
p1=(substr(s1,position,1))
p2=(substr(s2,position,1))
if ( p1 == p2 )
(total = total + 1)
}
print (total/length(s1)) " for shift "shift" and total "total
total=0
}
}'
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