The Caeser Cipher
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It encrypts a message by shifting each of the letters down three positions in the alphabet, wrapping back around to A if the shift reaches Z.
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The Caesar cipher is super easy to break: to decrypt a given ciphertext,
simply shift the letters three positions back to retrieve the plaintext. -
C A E S A R → F D H V D U
The Vigenere Cipher
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Letters aren’t shifted by three places but rather by values defined by a key, a collection of letters that represent numbers based on their position in the alphabet.
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If the key is DUH, letters in the plaintext are shifted using the
values 3, 20, 7 because D is three letters after A, U is 20 letters after A, and H
is seven letters after A. -
T H E Y D R I N K T H E T E A → W B L B X Y L H R W B L W Y H
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The group of three letters WBL appears twice in the ciphertext at nine-letter intervals. This suggests that the same three-letter word was encrypted using the same shift values, producing WBL each time. A cryptanalyst can then deduce that the key’s length is either nine or a value divisible by nine (that is, three).
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Cryptanalyst may also determine DUH as a possible encryption key.