Challenge 9: Implement PKCS#7 padding
Challenge 10: Implement CBC mode
Challenge 11: An ECB/CBC detection oracle
Challenge 12: Byte-at-a-time ECB decryption (Simple)
Challenge 13: ECB cut-and-paste
Challenge 14: Byte-at-a-time ECB decryption (Harder)
Challenge 15: PKCS#7 padding validation
Challenge 16: CBC bitflipping attacks
