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ECC based hybrid encryption decryption in Python

Python

ECC-Based Hybrid Encryption / Decryption in Python

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  • main.py
  • requirements.txt
main.py
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from tinyec import registry
from Crypto.Cipher import AES
import hashlib, secrets, binascii

def encrypt_AES_GCM(msg, secretKey):
  aesCipher = AES.new(secretKey, AES.MODE_GCM)
  ciphertext, authTag = aesCipher.encrypt_and_digest(msg)
  return (ciphertext, aesCipher.nonce, authTag)

def decrypt_AES_GCM(ciphertext, nonce, authTag, secretKey):
  aesCipher = AES.new(secretKey, AES.MODE_GCM, nonce)
  plaintext = aesCipher.decrypt_and_verify(ciphertext, authTag)
  return plaintext

def ecc_point_to_256_bit_key(point):
  sha = hashlib.sha256(int.to_bytes(point.x, 32, 'big'))
  sha.update(int.to_bytes(point.y, 32, 'big'))
  return sha.digest()

curve = registry.get_curve('brainpoolP256r1')

def encrypt_ECC(msg, pubKey):
  ciphertextPrivKey = secrets.randbelow(curve.field.n)
  sharedECCKey = ciphertextPrivKey * pubKey
  secretKey = ecc_point_to_256_bit_key(sharedECCKey)
  ciphertext, nonce, authTag = encrypt_AES_GCM(msg, secretKey)
  ciphertextPubKey = ciphertextPrivKey * curve.g
  return (ciphertext, nonce, authTag, ciphertextPubKey)

def decrypt_ECC(encryptedMsg, privKey):
  (ciphertext, nonce, authTag, ciphertextPubKey) = encryptedMsg
  sharedECCKey = privKey * ciphertextPubKey
  secretKey = ecc_point_to_256_bit_key(sharedECCKey)
  plaintext = decrypt_AES_GCM(ciphertext, nonce, authTag, secretKey)
  return plaintext

msg = b'Text to be encrypted by ECC public key and ' \
b'decrypted by its corresponding ECC private key'
print("original msg:", msg)
privKey = secrets.randbelow(curve.field.n)
pubKey = privKey * curve.g

encryptedMsg = encrypt_ECC(msg, pubKey)
encryptedMsgObj = {
'ciphertext': binascii.hexlify(encryptedMsg[0]),
'nonce': binascii.hexlify(encryptedMsg[1]),
'authTag': binascii.hexlify(encryptedMsg[2]),
'ciphertextPubKey': hex(encryptedMsg[3].x) + hex(encryptedMsg[3].y % 2)[2:]
}
print("encrypted msg:", encryptedMsgObj)

decryptedMsg = decrypt_ECC(encryptedMsg, privKey)
print("decrypted msg:", decryptedMsg)