Difference between the Substitution Technique and the Transposition Technique

There are numerous encryption techniques available for protecting sensitive data. Substitution and transposition techniques are the primary techniques of codifying the plaintext message to obtain the ciphertext. These two approaches are the fundamental building blocks of encryption techniques and can be combined to form a product cipher.

The substitution technique differs from the transposition technique in that the substitution technique replaces the plaintext characters for other characters, numbers, and symbols. In contrast, the Transposition techniques don't change the character but rather shift the symbol's position.

In this article, you will learn about the difference between substitution and transposition techniques. But before discussing the differences, you must know about substitution and transposition techniques with their features.

What is Substitution Technique?

The substitution technique involves replacing letters with other letters and symbols. In simple terms, the plaintext characters are substituted, and additional substitute letters, numerals, and symbols are implemented in their place. The Caesar cipher employs the substitution technique. In this technique, the alphabet is substituted with the alphabet three positions forward of the line. The substitution cipher technique was invented by Julius Caesar and named after him as the Caesar Cipher.

Let's take an easy example to understand this technique. The plaintext "JUMP" will be turned into "MXPS" using Caesar Cipher. Following the Caesar cipher, various substitution techniques were developed, including the Mono-alphabetic cipher, Polyalphabetic substitution cipher, Polygram substitution cipher, Playfair cipher, Homophobic substitution cipher, and Hill cipher.

The Caesar cipher was the weakest technique, but as the techniques evolved from time to time, the new version became stronger. The substitution technique's weakness is that it is highly predictable, and if the translation table is known, the substitution may be disrupted.

Features of Substitution Technique

There are various features of the substitution technique. Some features of substitution techniques are as follows:

1. In the substitution cipher technique, the letters in plain text are substituted by other letters, numbers, or symbols.
2. A character's identity is changed, but its place remains constant in the substitution technique.
3. Some algorithms that use the substitution technique are monoalphabetic substitution cipher, Playfair cipher, and polyalphabetic substitution cipher.
4. The substitution cipher approach allows for the detection of plain text by low-frequency letters.
5. Caesar Cipher is an example of the substitution cipher technique.

What is Transposition Technique?

In the transposition technique, the characters' identities are kept the same, but their positions are altered to produce the ciphertext. A transposition cipher in cryptography is a type of encryption that scrambles the locations of characters without altering the characters themselves. Transposition ciphers produce a ciphertext that is a permutation of the plaintext by rearranging the components of the plaintext in accordance with a regular method. It is distinct from substitution ciphers, which don't replace the unit's positions of plaintext but instead substitute the units themselves. A bijective function is utilized to the character locations to encrypt data, and an inverse function is employed to decode data. It is not a very secure technique.

Rail Fence encryption is a sort of transposition cipher that acquires its name from how it is encrypted the data. The plaintext is written down and diagonally on successive "rail" of an artificial fence in the rail fence and then pushed up when you get to the bottom. After that, the message is read aloud in a row-by-row fashion.

The Rail Fence Cipher is based on an old Greek mechanical device for building a transposition cipher that follows a fairytale-like pattern. The mechanism consisted of a cylinder with a ribbon wrapped around it. The encrypted message was written on the coiled ribbon. The characters of the original message were rearranged when the ribbon was uncoiled from the cylinder. The message was decrypted when the ribbon was wrapped in a cylinder with a similar diameter to the encrypting cylinder.

Features of the Transposition Technique

There are various features of the transposition technique. Some main features of the transposition techniques are as follows:

1. The keys that are closer to the proper key in the transposition cipher technique can reveal plain text.
2. The transposition cipher approach does not exchange one sign for another but rather moves the symbol.
3. The two most common types of transposition cipher are keyless and keyed transpositional cipher.
4. The Reil Fence Cipher is an excellent instance of a transposition tehnique.
5. The position of the character is modified in the transposition cipher technique, but the character's identity remains unchanged.

Key Differences between Substitution Technique and Transposition Technique

There are various key differences between Substitution Technique and Transposition Technique. Some main key differences between these techniques are as follows:

1. The substitution approach employs a substitute for the plaintext characters to transform them into ciphertext. In contrast, the transposition technique essentially rearranges the plaintext characters.
2. The substitution technique aims to change the entity's identification. In contrast, the transposition technique affects the entity's position instead of its identity.
3. The substitution technique replaces every character with an integer, character, and symbol. In contrast, in the transposition technique, every character has been positioned from its actual position.
4. Some algorithms that use the substitution technique are monoalphabetic, polyalphabetic substitution cipher, and Playfair cipher. In contrast, the transposition techniques utilize the keyed and keyless transpositional ciphers.
5. The plaintext in the substitution strategy could be easily determined using the low-frequency letter. In contrast, in the transposition technique, the keys close to the right key lead to the plaintext discovery.

Head-to-head comparison between the Substitution Technique and Transposition Technique

Here, you will learn the head-to-head comparisons between the Substitution Technique and Transposition Technique. The main differences between the Substitution Technique and Transposition Technique are as follows:

Conclusion

Substitution cipher and Transposition cipher are both classical techniques in cryptography, but these techniques are now outdated. Transposition ciphers shift each character of a string to another position. In contrast, the substitution ciphers replace every character in a string with a different number, character or symbol.