Monoalphabetic substitution ciphers utilize one cipher alphabet
can consist of any type of symbol or set of symbols as long a specific cleartext
unit will always encode to the same cipher text unit and each cipher text unit
will always decode to the same clear text unit. I say unit, as an abstraction,
because monoalphabetic substitution ciphers can be classified as one of two
methods of encryption: uniliteral ciphers and multiliteral ciphers. This will
be explained in depth later but for now just assume that a unit means a single
symbol [clear or cipher ].
2. Systematically Mixed Sequences
3. Random Sequences
secure  by relatively secure I mean that if the cryptanalyst knows the type
of cipher and is attacking the key then neither is more secure than the other
because both only have 25 possible keys [25 possible shifts or rotations, as in
the Caesar cipher, which makes these a special subclass of a monoalphabetic
substitution cipher known as a displacement ciphers].
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

Alphabet] the encrypted message would be: GSRH RH Z HVXIVG NVHHZTV.
order [the form follows from A  Z].
the alphabet is written out. If the keyword is E V E R C R A C K it is reduced to
E V R C A K and the below clear text to clear text alphabet results. Again, the
message: THIS IS A SECRET MESSAGE
Clear Alphabet

E

V

R

C

A

K

B

D

F

G

H

I

J

L

M

N

O

P

Q

S

T

U

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

encrypts to: FPOG OG V GZWXZF LZGGVQZ.
unit. If the cryptanalyst attacks the key, the solution space is much greater
than the previous method. If the cryptanalyst is using a generalized solution
[that applies to all uniliteral, monoalphabetic substitution ciphers], like
EverCrack, then the methods are equally "difficult"  a generalized solution
covers all (26!  1) possible random cipher alphabets [which includes all of
the above].
a brute force attack on modern computers would still take a while. A brute force
attack would equate to a permutation attack against the alphabet itself. On my
500 MHz laptop a permutation of 11 letters [39, 916, 800 permutations] took
approximately 25 minutes. For a permutation of 26 letters [403, 291, 461, 126
605, 635, 584, 000 ,000 permutations] is roughly 10 pentillion times greater
than the permutation of 11 letters it would be suffice to say that it would
take 480, 560, 378, 380, 273 years to solve to perform a permutation attack
on the cipher alphabet.
specific languages occur in fairly regular frequencies or percentage of a text.
This is because languages tend to be redundant [and some phonemes and letter
combinations easier to verbalize are used more frequently]. By redundant I
mean that most words [especially longer words] tend to have repetitive letters
[e.g., "repetitive" has three letters, 'e', 't', and 'i', that occur more than
once].
Letter

Percentage

Letter

Percentage

E

12.77

C  2.96 
T

8.55

M  2.88 
O

8.07

P  2.23 
A

7.78

Y  1.96 
N

6.86

W  1.76 
I

6.67

G  1.74 
R

6.51

B  1.41 
S

6.22

V  1.12 
H

5.95

K  .74 
D

4.02

J  .51 
L

3.72

X  .27 
U

3.08

Z  .17 
F

2.97

Q  .8 
properties of the underlying clear message, in a monoalphabetic substitution
cipher, the cipher text letters will tend to exhibit the same frequency
distribution so most letters can be easily guessed.
EverCrack does not use frequency analysis. It uses a comparison and reduction
approach based on the patterns of the cipher words. The full description of how
it works EverCrack Kernel.
and the online tool is EverCrack Tool
A uniliteral cipher consists of replacing each clear symbol with a
stitution cipher  there is always a onetoone correspondence between cleartext
units and cipher text units. Here the difference between a unit and a symbol
emerges  in multiliteral ciphers the single cleartext symbol is replaced by more
than one ciphertext symbol [a polygraph].
clear text message.
Specific Uniliteral Monoalphabetic Substitution Ciphers
A multiliteral cipher consists of replacing each clear symbol
resent a single clear symbol, then using the following plain and cipher alphabets:
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

ZY

XW

VU

TS

RQ

PO

NM

LK

JI

HG

FE

DC

BA

AB

CD

EF

GH

IJ

KL

MN

OP

QR

ST

UV

WX

YZ

clear text message: T H I S I S A S E C R E T M E S S A G E
cipher text message: MNLKJIKL JIKL ZY KLRQVUIJRQMN BARQKLKLZYNMRQ
uniliteral cipher  just a little extra manual work. It should be obvious that
it is not a uiliteral cipher because it would then be an anomolous message
consisting of five words, three of which are quite lengthy [words of specific
lengths also tend to have specific frequency distributions].
discovered that every language has a characteristic pattern to the distribution
of the letters that comprise that language. That property of language is a ref
erence that can be used to perform cryptanalysis. In this case, to make the
cipher more difficult to solve, that property of the language has been trivially
disguised.
with uniliteral monographs [the conversion is arbitrary] to then feed into the
EverCrack Monoalphabetic Substutition Cipher Cracker to crack the message.
Monographic ciphers are created by encrypting only one plain
not make a difference]. All of the previous plaincipher alphabets have used
this method. The important factor resulting from this method is, if only
alphabetical characters are encrypted [in contrast to punctuation and numbers],
there will always be a pool of 26 [or less] unique clear symbols and cipher
symbols.
distribution of the clear letters comprising the clear message.
Polygraphic ciphers are created by encrypting more than one
symbols encrypt to does matter]. Although, since we are still dealing with
monoalphabetic substitution ciphers at this point, the correspondence between
clear text units and cipher text units is still onetoone, this type of
cipher is considerably more difficult to crack than a monographic cipher. Out of
the 26 letters, a pool of 676 digraphs can be constructed [although many di
graphs, BX, never actually appear in clear text]. Thus, there must be a
few hundred cipher digraphs to account for the clear digraphs [that are en
crypted] depending on the size of the message.
contain an equal number of letters a "cipher pad" can be used]:
Clear Digraphs

TH

IS

AS

EC

RE

TM

ES

SA

GE

Cipher Digraphs

AB

CD

EF

GH

IJ

KL

MN

OP

QR

with a resulting cipher text of: AB CD CD EF GH IJ KL MN OP QR
the number of clear symbols and the number of cipher units  in this case, less
cipher units result using polygraphic enciphering. This not only hides the
frequency distribution of the text but also the number of underlying symbols per
se! This means that a different form of frequency analysis must be performed:
digraphic frequency analysis [or polygraphic in general]