Which type of cipher is characterized by encrypting letters with another letter in a one-to-one relationship?

The type of cipher characterized by encrypting letters with another letter in a one-to-one relationship is known as a substitution cipher. In this method of encryption, each letter in the plaintext is replaced with a letter from a fixed system to produce the ciphertext. This one-to-one relationship means that for every unique letter in the original message, there is a specific corresponding letter in the encrypted message.

Substitution ciphers can be simple, like the Caesar cipher, where each letter is shifted a fixed number of places down the alphabet, or more complex, involving random or predefined mappings of the alphabet that don't follow a simple pattern. This can include use cases like keyword ciphers, where the key determines the substitution.

Understanding this concept is crucial because it lays the foundation for recognizing how classic cryptographic techniques work, as well as understanding their strengths and vulnerabilities. This methodology is distinctly different from other forms of encryption, such as transposition ciphers, where the position of the letters is altered rather than their identity, or stream ciphers, which encrypt data one bit or byte at a time, typically using a keystream. A hybrid cipher combines two or more cipher techniques, but it does not specifically rely on the straightforward one-to-one mapping central to substitution c