def ciphertext_oracle():
ecb_ciphertext = base64.b64decode(open('25.txt', 'r').read())
ecb_key = b'YELLOW SUBMARINE'
ecb_cipher = AES.new(ecb_key, AES.MODE_ECB)
plaintext = ecb_cipher.decrypt(ecb_ciphertext)
cipher = challenge18.CTR(AES.new(key, AES.MODE_ECB), nonce)
return cipher.encrypt(plaintext)
def encryptParams(userdata):
userdata = userdata.replace(';', '%3B').replace('=', '%3D')
x1 = b'comment1=cooking%20MCs;userdata='
x2 = b';comment2=%20like%20a%20pound%20of%20bacon'
params = x1 + userdata.encode('ascii') + x2
cipher = challenge18.CTR(AES.new(key, AES.MODE_ECB), nonce)
return cipher.encrypt(util.padPKCS7(params, 16))
def edit(ciphertext, offset, newtext):
cipher = challenge18.CTR(AES.new(key, AES.MODE_ECB), nonce)
cipher.encrypt(b'\x00' * offset)
return ciphertext[0:offset] + cipher.encrypt(newtext)
def decryptParamsAndCheckAdmin(encryptedParams):
cipher = challenge18.CTR(AES.new(key, AES.MODE_ECB), nonce)
paddedParams = cipher.decrypt(encryptedParams)
params = challenge15.unpadPKCS7(paddedParams)
return params.find(b';admin=true;') != -1
def encryptString(s):
cipher = challenge18.CTR(AES.new(key, AES.MODE_ECB), 0)
return cipher.encrypt(s)