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Python 3 EV2 authentication/secure messaging implementation according to AN12196. Featuring Leakage Resilient Primitive (LRICB and LRP-CMAC) from AN12304. Pull requests welcome.
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ev2.py
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test_cipher_vec.py
test_ev2.py
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test_lrp_cmac_vectors.py
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README.md

NTAG424 EV2/LRP cryptography example

  • AuthenticateEV2 - perform authentication with PICC;
  • CryptoComm - sign/encrypt APDUs and validate responses;
  • LRP - perform CTR mode encryption/decryption or CMACing with Leakage Resilient Primitive.

This code was written according to the publicly available application note AN12196 "NTAG 424 DNA and NTAG 424 DNA TagTamper features and hints".

Pull requests welcome.

Note: NTAG — is a trademark of NXP B.V.

Usage

EV2

Please refer to test_ev2.py and cross-check it with the application notes. There are also some docstrings in the ev2.py file.

  • AuthenticateEV2 - helper for performing AuthenticateEV2First handshake with PICC:
    • init - generate the initial C-APDU to start authentication;
    • part1 - generate a response to first R-APDU from PICC;
    • part2 - verify second R-APDU from PICC, initialize authenticated session;
  • CryptoComm - a class which represents "authenticated session":
    • wrap_cmd - construct C-APDU in given CommMode, convenience wrapper;
    • unwrap_res - parse R-APDU in given CommMode, convenience wrapper;
    • sign_apdu - convert CommMode.PLAIN C-APDU into CommMode.MAC;
    • encrypt_apdu - convert CommMode.PLAIN C-APDU into CommMode.FULL;
    • parse_response - parse R-APDU and verify it's MAC signature (CommMode.MAC response);
    • decrypt_response - decrypt the response data parsed by validate_response (CommMode.FULL response);

LRP

LRICB Encryption (LRICBEnc) and decryption (LRICBDec):

from lrp import LRP

import binascii

# the original key
key = binascii.unhexlify("E0C4935FF0C254CD2CEF8FDDC32460CF")
# plaintext data to encrypt
pt = binascii.unhexlify("012D7F1653CAF6503C6AB0C1010E8CB0")
# also sometimes called "counter"
iv = binascii.unhexlify("C3315DBF")

# encrypt plaintext
lrp = LRP(key, 0, iv, pad=True)
ct = lrp.encrypt(pt)

# decrypt the stuff back
lrp = LRP(key, 0, iv, pad=True)
pt = lrp.decrypt(ct)

MACing (LRP-CMAC/CMAC_LRP):

from lrp import LRP

import binascii

key = binascii.unhexlify("8195088CE6C393708EBBE6C7914ECB0B")
lrp = LRP(key, 0, b"\x00" * 16, pad=True)
mac = lrp.cmac(binascii.unhexlify("BBD5B85772C7"))
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