building dissector for TREL packets in wireshark

[pranay-grl]

Decription : i am trying to build a dissector for TREL packets in wireshark , i have followed discussion 9267 ,

i got packet captures related to TREL packets , i got to know that KeyManager::ComputeTrelKey is used to generate the trel key i have generate trel key code below

import hashlib
import hmac
import binascii
 
def hkdf(key, salt, output_length):
  
  """
  Trel key generation
  Derives a new key from an input key using HMAC-based Extract-and-Expand.
  Args:
    key: The input key.
    salt: A random value used to make the derived key more secure.
    output_length: The desired length of the derived key.
  Returns:
    The derived key.
  """

  prk = hmac.digest(key, salt, hashlib.sha256)
  output = prk
  while len(output) < output_length:
    output += hmac.digest(output, prk, hashlib.sha256)
  output = output[:output_length]
  return output

def main():
  key_in_hex = '00112233445566778899aabbccddeeff'
  key_in_bytes= binascii.unhexlify(key_in_hex)
  salt_in_hex = "0000000054687265616453657175656e63654d61737465724b6579"  
  salt_in_bytes = binascii.unhexlify(salt_in_hex)
  output_length = int("32", 10)
  derived_key = hkdf(key_in_bytes, salt_in_bytes, output_length)
  hex_string =""
  for byte in derived_key:
    hex_string += f"{byte:02x}"

  print("Derived Trel key:",hex_string)
  last_16_bytes = hex_string[-32:]
  print(last_16_bytes)
if __name__ == "__main__":
  main()

salt in above code is seq_counter= 00000000 + 'ThreadSequenceMasterKey'
key is standard key thread-spec 1.3

Generated key
Derived Trel key: 7c6f79a038331379e9cbb0cda64689894c2b543e32571dae4ebb48a9ab559581

data i need to decode hex string (trel packet payload)
dce55bc70cd8dce55bcce09386dd6008a27a005d1140fdda38148394a8deccb9128bb9d93560fdda38148394a8de1938b620a9e05dc4de62bf23005d6aaf0018d464000000211243e48f16ae4a7341d8ba64d4ffff734aae168fe443127f3b01f04d4c4d4c784f001566650000000000000188092ced99faaa8a967d32bcefae3831c0e084c652f91b86281edefae2d33a87e8

Expectation : i want to decode above hex string with the key i generated if i generated correct key. and if key is correct how do decode string?

Any help would be appreciated.