2. Presented By
Ali Raza Fa-2020-BSSE-240
Waseem Akram Fa2020-BSSE-225
Tahir Manzoor Fa-2020-BSSE-235
3. What is Substitution Cipher?
Substitution Cipher is an encryption
technique that replaces individual
characters in a plaintext with different
characters to create ciphertext.
It has been used for thousands of years,
including by Julius Caesar.
A specific set of rules and parameters
used to encrypt and decrypt messages.
4. How Substitution Cipher Works?
Encryption Process
A substitution cipher encrypts
plaintext by replacing each
character with a different character
in the ciphertext.
Decryption Process
The decryption process is the
reverse of encryption, with each
character in the ciphertext being
replaced by the corresponding
character in the plaintext.
5. Types of Substitution Cipher
Caesar Cipher
Caesar cipher is a monoalphabetic substitution cipher in which each letter in the
plaintext is shifted a fixed number of places down the alphabet.
Monoalphabetic Cipher
Monoalphabetic cipher is a type of substitution cipher where each letter in the plaintext
is replaced with another letter based on a fixed substitution key.
Polyalphabetic Cipher
Polyalphabetic cipher, on the other hand, uses a series of different substitution
alphabets, thus rendering the frequency analysis much harder.
6. History and the Evolution of Substitution
Ancient
The earliest known use of
substitution ciphers can be traced
back to the ancient Greeks.
Modern
Throughout history, cryptography
advanced from simple ciphers to
complex machines like the Enigma.
The Future
The future of cryptography lies in
quantum computers and quantum
cryptography, which are still under
development.
7. Homophonic Substitution Cipher
Homophonic cipher is a substitution
algorithm used to provide a higher
level of encryption by substituting
multiple characters for each
character in the plaintext.
A homophonic algorithm is a complex
substitution cipher that replaces
plaintext characters with multiple
ciphertext characters, creating
ambiguity and making the cipher
more difficult to crack.
9. Selections of alphabetics
The first step in homophonic encryption is
the selection of alphabets. We select and
write all those alphabets which we are going
to replace into cipher text.
10. Creation of key
The key is the core of the encryption process.
It should link each letter of the alphabet to a
unique symbol or group of numeric symbols.
Each letter should have several possible
substitutions, making it hard to decipher.
11. Encryption
For each letter in your message, use the key
to substitute the letter with a numeric key
symbol respectively. Write down the numeric
symbols and send them to the receiver.
12. Decryption
To decrypt a message, you need the key that
was used to encrypt it. The key should link
each symbol to a corresponding letter. Write
down all letters and you'll get the original plain
message from cipher text.
13. Example
Words to Encrypt = HELLO WORLD
Homophonic Key
H : {2, 7}
E : {12, 3, 9}
L : {6, 8}
W : {1, 11}
O : {13, 4, 6}
R : {5, 8}
D : {10}
Ciphertext = 2 9 6 8 13 11 4 5 6 10
16. High Security
Homophonic encryption is much harder
to break than many other types of
encryption, making it ideal for use in
sensitive situations. It is also easy to
implement.
17. Low key complexity
Unlike other encryption methods, homophonic
encryption keys can be relatively simple to
create, while still providing excellent security.
Its key is easy to make just we had to allocate
the different numeric values to each
alphabetic
18. Easy to Learn
Homophonic encryption can be taught to
anyone with basic computer skills, making it
accessible and effective for those who are
unfamiliar with other encryption methods.it is
easy to learn and also easy to implement
19. Limitations of Homophonic
Algorithms
Homophonic algorithms can be slower than other encryption
methods due to the amount of ciphertext they generate.
They may require more computational power to decipher.
They can generate longer ciphertexts than other encryption
methods, creating storage issues.
20. Applications of Homophonic
Algorithms
Military Communication
Ensuring sensitive and confidential information cannot be decoded by the
enemy.
Banking Security
play a critical role in banking security, encrypting custom..er data and
transactions, ensuring secure communication.
