The **Simple Substitution Cipher** is one of the most straightforward and commonly known encryption techniques. In this method, each letter in the plaintext is replaced with a letter from a fixed substitution alphabet. The cipher was used throughout history for various forms of communication, particularly in the early modern period, when simpler forms of cryptography were favored for their ease of use.

# Substitution

The **Playfair Cipher** is a manual symmetric encryption technique that encrypts pairs of letters (bigrams) instead of single letters. It was invented by **Charles Wheatstone** in **1854** but became known as the Playfair Cipher after it was promoted by **Lord Playfair**. This cipher was used extensively during the **World War I** era for secure military communications, as it provided better security than simple substitution ciphers by addressing frequency analysis vulnerabilities.

The **Homophonic Substitution Cipher** is a type of substitution cipher that enhances the security of traditional substitution ciphers by using multiple symbols or letters to represent a single plaintext character. This method was developed during the late **19th century** and became popular among cryptographers aiming to improve upon the weaknesses of earlier ciphers that could be easily broken through frequency analysis.

The **Hill Cipher** is a polygraphic substitution cipher developed by mathematician **L. K. Hill** in **1929**. It represents one of the first ciphers to use linear algebra, specifically matrix multiplication, to perform encryption, thus providing a more sophisticated method compared to earlier ciphers.

The *Alberti cipher*, created by **Leon Battista Alberti** in the **15th **century, is recognized as one of the earliest examples of a polyalphabetic substitution cipher. **Alberti**, an Italian Renaissance polymath, developed this cipher as a response to the need for stronger, more secure encryption methods that could withstand frequency analysis, a technique that had become effective against simpler monoalphabetic ciphers.

The *Affine cipher* is a type of substitution cipher rooted in modular arithmetic, which falls under the category of monoalphabetic ciphers. It has origins in classical cryptography, dating back to the use of basic substitution techniques by ancient civilizations. While there isn’t a single, clear creator or exact date for the invention of the affine cipher specifically, it embodies methods commonly attributed to early cipher systems used throughout history, such as by **Roman **and **Greek **scholars.

The *Vigenère Cipher* is a classical cryptographic method that enhances the security of simple substitution ciphers. It was developed by the French diplomat **Blaise de Vigenère** in the **16**th century.

The *Trifid Cipher* is a cryptographic technique that combines elements of substitution and transposition ciphers to encrypt messages. It was invented in **1901** by **Félix Delastelle**, a French cryptographer, and is known for its use of three-dimensional representations.

The *Templar Cipher* is a cryptographic method associated with the **Knights Templar**, a medieval Christian military order founded during the Crusades. It is one of the many historical ciphers that have been attributed to the **Knights Templar**, although the exact cipher they used remains a subject of debate and speculation.

The *Polyalphabetic Cipher* is a type of substitution cipher that enhances the security of traditional ciphers by introducing multiple alphabets or cipher alphabets. In this encryption technique, each letter of the plaintext is substituted with a corresponding letter from one of several different cipher alphabets, based on a secret key or keyword.