Transcript Cryptanalysis Example - index [METU Computer Engineering]

Cryptanalysis Example
Cipher text
cop raqv obl eqmp qipa cop kppr pmk
hxlc obip b hxcymw kxayme
gzbll
ptpgxcp bc obzv rblc vqxa lbw
bahbkyzzq cq gbzz yc qvv
Suppose ‘e’ is the most
common
cop raqv obl eqmp qipa cop kppr pmk
e
e
e
e ee e
fp hxlc obip b hxcymw kxayme gzbll
e
e
ptpgxcp bc obzv rblc vqxa lbw
e e
e
bahbkyzzq cq gbzz yc qvv
“the” may appear twice
cop raqv obl eqmp qipa cop kppr pmk
the
h
e
e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
t h e
t
ptpgxcp bc obzv rblc vqxa lbw
e e te t h
t
bahbkyzzq cq gbzz yc qvv
t
t
‘a’ is also common
cop raqv obl eqmp qipa cop kppr pmk
the
ha
e
e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
t ha e a
t
a
ptpgxcp bc obzv rblc vqxa lbw
e e te at ha
a t
a
bahbkyzzq cq gbzz yc qvv
a a
t
a
t
‘y’ must be ‘i’
cop raqv obl eqmp qipa cop kppr pmk
the
ha
e
e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
t ha e a
ti
i
a
ptpgxcp bc obzv rblc vqxa lbw
e e te at ha
a t
a
bahbkyzzq cq gbzz yc qvv
a a i
t
a
it
Is ‘l’ ‘s’?
cop raqv obl eqmp qipa cop kppr pmk
the
has
e
e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
ass
ptpgxcp bc obzv rblc vqxa lbw
e e te at ha
ast
sa
bahbkyzzq cq gbzz yc qvv
a a i
t
a
it
‘q’ must be ‘o’
cop raqv obl eqmp qipa cop kppr pmk
the
o has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
ass
ptpgxcp bc obzv rblc vqxa lbw
e e te at ha
ast o
sa
bahbkyzzq cq gbzz yc qvv
a a i o to a
it o
Double letters likely ‘l’
cop raqv obl eqmp qipa cop kppr pmk
the
o has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
lass
ptpgxcp bc obzv rblc vqxa lbw
e e te at hal
ast o
sa
bahbkyzzq cq gbzz yc qvv
a a illo to all it o
‘g’ into ‘f’?
cop raqv obl eqmp qipa cop kppr pmk
the
o has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
flass?
ptpgxcp bc obzv rblc vqxa lbw
e ef te at hal
ast o
sa
bahbkyzzq cq gbzz yc qvv
a a illo to fall it o
‘c’ is more likely
cop raqv obl eqmp qipa cop kppr pmk
the
o has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at hal
ast o
sa
bahbkyzzq cq gbzz yc qvv
a a illo to call it o
‘v’ possibilities
cop raqv obl eqmp qipa cop kppr pmk
the
od has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at hald? ast o
sa
bahbkyzzq cq gbzz yc qvv
a a illo to call it odd
‘f’ works better
cop raqv obl eqmp qipa cop kppr pmk
the
of has o e o e the ee e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half ast fo
sa
bahbkyzzq cq gbzz yc qvv
a a illo to call it off
“half mast” makes sense…
cop raqv obl eqmp qipa cop kppr pmk
the m of has o e o e the eem e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half mast? fo
sa
bahbkyzzq cq gbzz yc qvv
a a illo to call it off
But “half past” works better
cop raqv obl eqmp qipa cop kppr pmk
the p of has o e o e the eep e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
i
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half past fo
sa
bahbkyzzq cq gbzz yc qvv
a a illo to call it off
That must be “prof”!
cop raqv obl eqmp qipa cop kppr pmk
the prof has o e o er the eep e
fp hxlc obip b hxcymw kxayme gzbll
e
st ha e a
ti
ri
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half past fo r sa
bahbkyzzq cq gbzz yc qvv
ar a illo to call it off
‘i’ as ‘v’
cop raqv obl eqmp qipa cop kppr pmk
the prof has o e over the eep e
fp hxlc obip b hxcymw kxayme gzbll
e
st have a
ti
ri
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half past fo r sa
bahbkyzzq cq gbzz yc qvv
ar a illo to call it off
Only ‘d’ works here
cop raqv obl eqmp qipa cop kppr pmk
the prof has o e over the deep e d
fp hxlc obip b hxcymw kxayme gzbll
e
st have a
ti
d ri
class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half past fo r sa
bahbkyzzq cq gbzz yc qvv
ar adillo to call it off
First line solved!
cop raqv obl eqmp qipa cop kppr pmk
the prof has gone over the deep end
fp hxlc obip b hxcymw kxayme gzbll
e m st have a m tin d ring class
ptpgxcp bc obzv rblc vqxa lbw
e ec te at half past fo r sa
bahbkyzzq cq gbzz yc qvv
armadillo to call it off
Found the last vowel
cop raqv obl eqmp qipa cop kppr pmk
the prof has gone over the deep end
fp hxlc obip b hxcymw kxayme gzbll
e must have a mutin during class
ptpgxcp bc obzv rblc vqxa lbw
e ecute at half past four sa
bahbkyzzq cq gbzz yc qvv
armadillo to call it off
Finished!
cop raqv obl eqmp qipa cop kppr pmk
the prof has gone over the deep end
fp hxlc obip b hxcymw kxayme gzbll
we must have a mutiny during class
ptpgxcp bc obzv rblc vqxa lbw
execute at half past four say
bahbkyzzq cq gbzz yc qvv
armadillo to call it off