Python script to compare Java LazySodium signed messages with PyNaCl signed messages using Keypairs from both locations. Designed for Keyspace.

signature_checker.py

"""
(c) 2021 Keyspace

Compares a LazySodium / LibSodium output from Keyspace Android with PyNaCl's output and checks if LazySodium's signatures match PyNaCl's signature.

Note: LazySodium output on Android and PyNaCl output from this script must be the same due to determinism.
______________________________________________________________________________________________________________________________________________________


                                     .-------> Public key -----> Verify data         
    Seed ----> Generate keypair  ----|             |_______________________________. 
      |         on Android           |                                             | 
      |                              |                                             | 
      |                              '-------> Secret key -----> Signed data       | 
      |                                                               |            | 
      |                                                               |            | 
      |                                                               |            | 
      |                                                               V            | 
      |                              .-----> Verify key ---> [[ Verify data ]] <---' 
      '----> Generate keypair  ------|                                ^              
                 in Python           |                                |              
                                     |                                |              
                                     |                                |              
                                     '---->  Signing key -----> Signed data          

"""

# All of the below values come from Keyspace Android's logcat

hardenedSeed = "6123cc8cb10eb9a23585183428b2d692c58407a05e558362c00811b05ee21eb2"  # hardened seed from argon2i(bip39[seed]) output, to be used as input to keypair generation function

lazySodiumPrivateKey = "6123CC8CB10EB9A23585183428B2D692C58407A05E558362C00811B05EE21EB2629E8A3DFF89FD68A2D6721F0F41E032624140A8D13EE865A3E4AA46E3406D3C"
lazySodiumPublicKey = "629E8A3DFF89FD68A2D6721F0F41E032624140A8D13EE865A3E4AA46E3406D3C"

data = """{"expiry":1641032384056,"token":"e12de5ab-0891-45d1-adb0-a65f50491100","signedToken":"f0b5308927b9611574c3e865203719b85eee98aa243c00829f8b6f14e1731d5a"}""" # the actual message to sign.
androidSignedData = "4F46A31E6576F801D5670B9C741384EFC16E990721DF1051FC17AF91EE9CA7A1BFFCE6F8FB089593A84E8DC82AEBA26795242779686F6075F11BF09FC971E7037B22657870697279223A313634313033323338343035362C22746F6B656E223A2265313264653561622D303839312D343564312D616462302D613635663530343931313030222C227369676E6564546F6B656E223A2266306235333038393237623936313135373463336538363532303337313962383565656539386161323433633030383239663862366631346531373331643561227D"



import json
from nacl import encoding
from nacl.encoding import HexEncoder, Base64Encoder
from nacl.signing import SigningKey, VerifyKey, SignedMessage
from nacl.public import PrivateKey, PublicKey

androidSignedDataAsBytes = HexEncoder.decode((bytes(androidSignedData, encoding='utf-8')).decode())

androidSignature = androidSignedData[0:128]
androidSignatureAsBytes = HexEncoder.decode((bytes(androidSignature, encoding='utf-8')).decode())

dataAsBytes = bytes(data, encoding='utf-8')

print ("Data:\n" + data)
print ("Seed:\n" + hardenedSeed + "\n")


# On LazySodium Android, the private key from the seed was:
print ("Android LazySodium Private Key:\n" + lazySodiumPrivateKey) 
print ("Android LazySodium Public Key:\n" + lazySodiumPublicKey) 

private_key = SigningKey(bytes(hardenedSeed, encoding='utf-8'), encoder=HexEncoder)  # Generate a signing/secret/private key from the Android generated hardened seed
signed = private_key.sign(bytes(data, encoding='utf-8'))  # Sign message with the signing/secret/private key in PyNaCl

public_key = VerifyKey(bytes(lazySodiumPublicKey, encoding='utf-8'), encoder=HexEncoder)  # Generate a verification/public key from the Android public key hexString
verificationStatus = public_key.verify(dataAsBytes, androidSignatureAsBytes)



print ("\nPyNaCl message from signature:     \n" + str (signed.message) )
print ("Android pasted message from logcat:\n" + str (dataAsBytes) )

if signed.message == dataAsBytes: print ("\n[ ✓ ] Bytes match")
else: print ("\n[ x ] Error: Bytes do not match")



print ("\nPyNaCl produced signature:           \n" + str (signed.signature) )
print ("Android pasted signature from logcat:\n" + str (androidSignatureAsBytes) )

if signed == androidSignedDataAsBytes: print ("\n[ ✓ ] Bytes match")
else: print ("\n[ x ] Error: Bytes do not match")

print("\n**********************************************************************\n")

if verificationStatus:
    print ("[ ✓ ] MESSAGE VERIFIED!  :)")
else:
    print ("[ x ] INVALID / FORGED SIGNATURE!  :(")

Screenshot

---

Edit: Error fixed. Turns out, I was using sealed boxes on instead of signing in LazySodium Android. :)

Changes

Before

cryptoBoxSeedPair()
cryptoSign()
cryptoSignVerify()

After

cryptoSignSeedPair()
cryptoSign() cryptoSignDetached() (changed to combined mode)
cryptoSignVerifyDetached() (detached verification function works for both combined mode and detached mode signatures)