This is the 7th day of my participation in the August More Text Challenge

1.4 Frequency analysis to crack Caesar encryption

Password stick

In the 5th century BC, the Spartans used a wooden stick, wrapped in leather or parchment, to write a message horizontally on it, and took off the belt. The long string of letters makes no sense when unfolded. The recipient then wraps the belt around the same stick to retrieve the message.

In 404 BC, a wounded messenger arrived in front of the Spartan general Lisander. Only he and his four companions survived the Persian journey. Lisander took the belt and wound it around his cryptostick, knowing that the Persian Fanapazus was preparing to attack him.

Frequency analysis decryption method

Isn’t the password stick too simple?

The cipher chooses to replace the letter of the message with another letter, such as writing a as a 1, so that the decryptor cannot directly access the message.

In order to determine the frequency of occurrence of each English letter, analyze one or more ordinary English articles. The most frequent occurrence of the English letter is E, followed by T, and then A… Then check the ciphertext to be cracked and sort out the frequency of each letter. Assume that the letter with the highest frequency in the ciphertext is J, then it may be the substitute of E; if the letter with the second highest frequency in the cipher text is P, then it may be the substitute of T, and so on to unlock the content of the encrypted message. That’s frequency analysis.

  • The process of comparing the frequency of a plaintext letter to that of a ciphertext letter
  • Substitution ciphers can be easily deciphered by analyzing the frequency of each symbol
  • In every language, the alphabet in a long text shows a discernible frequency.
  • E is the most commonly used letter in the English language, appearing one in eight times