Substitution Cipher Solver
Interactive tool for solving simple substitution ciphers using frequency analysis.
Solving Tips
- • Most common English letters: E, T, A, O, I, N
- • Single-letter words are usually A or I
- • THE is the most common 3-letter word
- • Double letters: LL, SS, EE, OO, TT are common
- • Look for patterns like _HE (THE, SHE, CHE)
What is a Substitution Cipher?
A simple substitution cipher replaces each letter in the plaintext with a different letter from the alphabet. Each letter maps to exactly one other letter consistently throughout the message.
Solving Substitution Ciphers
Frequency Analysis
The most common approach is to analyze letter frequencies:
- E is the most common letter in English (~12.7%)
- T, A, O, I, N are next most common
- Compare ciphertext frequencies to expected frequencies
- Match high-frequency cipher letters to common English letters
Pattern Recognition
- Single letters: Usually A or I
- Two-letter words: OF, TO, IN, IS, IT, AS, AT, BE, WE
- Three-letter words: THE, AND, FOR, ARE, BUT
- Double letters: LL, SS, EE, OO, TT common
Substitution Ciphers in Geocaching
These ciphers are extremely common in geocaching because:
- Challenge level: Requires thinking but is solvable
- Classic puzzle: Well-known cipher type
- Customizable: Any alphabet can be used
- Educational: Teaches cryptanalysis basics
Common Substitution Types
- Caesar: Shifted alphabet
- Atbash: Reversed alphabet
- ROT13: Shifted by 13
- Random: Arbitrary letter mapping
- Keyword: Based on a keyword
Solving Strategy
- Count letter frequencies
- Identify likely E, T, A mapping
- Look for THE pattern
- Fill in common words
- Use word patterns for remaining letters