EverCrack Open Source Cryptanalysis

The Atbash Cipher is another special implementation of a mono-

alphabetic substitution cipher [also uniliteral]. The Atbash Cipher inverts the

clear alphabet to create the cipher alphabet:

Clear Alphabet

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

Cipher Alphabet

Z

Y

X

W

V

U

T

S

R

Q

P

O

N

M

L

K

J

I

H

G

F

E

D

C

B

A

Effectively, the enciphering alphabet is a simple reverse, direct

standard alphabet [it is in normal order yet reversed].

Thus the plain text message: T H I S I S A S E C R E T M E S S A G E

becomes the cipher text: G S R H R H Z H V X I V G N V H H Z T V

The Atbash Cipher relies on the secrecy of the method. If the

method is known it is the least secure of all ciphers because there is only one

possible key [effectively, ROT 25].

A Caesar Cipher is a specific type of a monoalphabetic substitution

cipher [as well as being uniliteral]. The Caesar is the next simplest form of

substitution cipher. The Caesar Cipher works by taking a plain text message:

T H I S I S A S E C R E T M E S S A G E and rotating (or shifting)

each letter

of the alphabet by a specified number [and wrapping around after Z to the start

of the alphabet]. Hence, if the "key" is 7 rotations the cipher alphabet would

be as follows:

Clear Alphabet

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

Cipher Alphabet

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

B

C

D

E

F

G

with a resulting cipher text of: A O P Z P Z H Z L J Y L A T L Z Z H N L

The Caesar Cipher uses a standard, direct cipher alphabet [A - Z order].

Cryptanalysis of a Caesar Cipher is trivial. Since there can only be

25 possible cipher alphabets [keys] you simply need to test each possible cipher

alphabet against the encrypted message. The Caesar Cipher Cracker automates

this process by implementing a brute-force key attack and comparing each result to

dictionary words until a proper decode is found.

The Affine Cipher is also a special implementation of a mono-

alphabetic substitution cipher. The Affine Cipher is only more complex in its

method of encryption - not in the encrypted results.

In the Caesar Cipher we simply added to the value of the plain

letter [the number of positions to rotate] whereas the Affine Ciphers specifies

rotating by a specific multiplier [with an optional adder]. This only

means, if the alphabet is viewed in the analog, modular fashion of a clock, that

the target letter used to encipher can be at a further spot. Thus, if "B" is

multiplied by 3 and 1 is added, the encrypted letter would be "E";

E(X) = M(X) + A(mod 26)

where the letter "X" is (E)ncrypted by (M)ultiplying by "M" and (A)dded to that

value is a number between 1 and 25 (inclusive). Sounds complicated, which for

the level of security over the Caesar Cipher it is. It adds no extra security

but adds extra complexity. In its time it probably was a good method for

foiling cryptanalysts who had not seen anything more complicated than the Caesar

Cipher [since in both these cases we have secret algorithm ciphers] but the

resulting cipher text is weak. It is just a different method for gen-

erating a cipher alphabet - an alphabet that is not as easily detected to be

shiftted as the Caesar Cipher is.

Note: the strength of a secret algorithm cipher lies in

methods, this cipher was more secure than the Caesar Cipher. The fact is, the

security of a cipher can depend upon who is doing the cryptanalyzing - what

knowledge they bring to the task.