Question 1

What is a substitution cipher?

Accepted Answer

A monoalphabetic substitution cipher replaces each letter with another letter consistently throughout the message. Unlike Caesar cipher which shifts all letters by the same amount, a substitution cipher can use any mapping (A→Q, B→X, C→M, etc.). This creates 26! possible keys.

Question 2

How do I solve a substitution cipher?

Accepted Answer

Start with frequency analysis - E, T, A, O, I, N are the most common English letters. Look for single-letter words (A, I) and common short words (THE, AND, FOR). Identify common patterns like double letters (LL, SS, EE) and word endings (-ING, -TION, -ED). Build up the solution gradually.

Question 3

What are bigrams and trigrams?

Accepted Answer

Bigrams are two-letter combinations (like TH, HE, IN), while trigrams are three-letter combinations (like THE, AND, ING). In English, TH is the most common bigram and THE is the most common trigram. Analyzing these patterns helps identify letter mappings.

Question 4

How does word pattern matching help?

Accepted Answer

Words have unique patterns based on repeated letters. For example, THAT has pattern ABAB, and PEOPLE has pattern ABCADB. By matching ciphertext word patterns against dictionary words, you can identify potential plaintext words and their letter mappings.

Substitution Cipher Solver

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