MISTasks/Technical/picoCTF/t1/q2.md

Question: Easy1

Key: picoCTF{CRYPTOISFUN}

Core concept: Vigenere Cypher - Decrypted character=(Encrypted character−Key character+26)mod26

Can be solved by an easy Python script:

def decrypt_vigenere(encrypted_text, key):
    decrypted_text = ""
    key_length = len(key)

    for i in range(len(encrypted_text)):
        encrypted_char_pos = ord(encrypted_text[i]) - ord('A')
        key_char_pos = ord(key[i % key_length]) - ord('A')

        decrypted_char_pos = (encrypted_char_pos - key_char_pos + 26) % 26

        decrypted_char = chr(decrypted_char_pos + ord('A'))

        decrypted_text += decrypted_char

    return decrypted_text


encrypted_flag = "UFJKXQZQUNB"
key = "SOLVECRYPTO"

decrypted_flag = decrypt_vigenere(encrypted_flag, key)
print("Decrypted Flag:", decrypted_flag)

Output: CRYPTOISFUN