You have found an old ciphertext, where you know that the plaintext discusses cryptographic methods. You suspect that a Vigenere cipher has been used and therefore look for repeated strings in the ciphertext.
You nd that the string TICRMQUIRTJR occurs twice in the ciphertext. The rst occurrence starts at character position 10 in the text and the second at character position 241 (we start counting from 1).
You make the inspired guess that this ciphertext sequence is the encryption of the plaintext word cryptography. If this guess is correct, what is the key? Hint : Analyze the possible periods.