The caesar cipher is a type of substitution cipher where each letter in the plaintext is shifted a certain number of places down or up the alphabet. For example, with a shift of 3, A becomes D.
Problem with caesar cipher
The frequency of letters in the ciphertext matches the frequency of letters in the plaintext, making it vulnerable to frequency analysis and deduce the mapping. To break the caesar cipher, there are two methods.
- Brute force Try all 25 possible shifts until the plaintext is revealed.
- Frequency analysis Analyse the frequency of letters in the ciphertext and match them to the expected frequency of the letters in the language of plaintext.
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