Implementing-cryptography-using-python

268 Chapter 9 ■ Mastering Cryptography Using Python
# decrypt using Diffie-Hellman - ECC
def decrypt_dh(ciphertext, dhSecret):
# decrypt using the shared secret from Client (Private) and Server
(Public)
ciphertext = ciphertext.decode('utf-8')
plaintext = decrypt_AES_GCM(ciphertext,dhSecret)
#reverse = encrypt_AES_GCM(ciphertext, dhSecret)
return plaintext
# generate ECC certs
def gen_ecc_certs():
key = ECC.generate(curve='P-256')
f = open('myprivatekey.pem','wt')
f.write(key.export_key(format='PEM'))
f.close()
f = open('myprivatekey.pem','rt')
key = ECC.import_key(f.read())
print (key)
# encrypt using AES-GCM
def encrypt_AES_GCM(msg, secretKey):
aesCipher = AES.new(secretKey, AES.MODE_GCM)
ct, authTag = aesCipher.encrypt_and_digest(msg)
ct = hexlify(ct)
ct = ct.decode('utf-8')
authTag = hexlify(authTag)
authTag = authTag.decode('utf-8')
noncea = hexlify(aesCipher.nonce)
nonce = noncea.decode('utf-8')
ciphertext = json.dumps({'nonce':nonce, 'ciphertext':ct,
'tag':authTag})
return ciphertext
# decrypt using AES-GCM
def decrypt_AES_GCM(encryptedMsg, secretKey):
b64 = json.loads(encryptedMsg)
nonce = str(b64['nonce'])
nonce = nonce.encode()
nonce = unhexlify(nonce)
ct = str(b64['ciphertext'])
ct = ct.encode()
ct = unhexlify(ct)