1  """
 2  This module is for generating ack payload
 3  """
 4  
 5  from binascii import hexlify
 6  from struct import pack
 7  
 8  from . import helper_random
 9  from . import highlevelcrypto
10  from .addresses import encodeVarint
11  
12  
13  def genAckPayload(streamNumber=1, stealthLevel=0):
14      """
15      Generate and return payload obj.
16  
17      This function generates payload objects for message acknowledgements
18      Several stealth levels are available depending on the privacy needs;
19      a higher level means better stealth, but also higher cost (size+POW)
20  
21         - level 0: a random 32-byte sequence with a message header appended
22         - level 1: a getpubkey request for a (random) dummy key hash
23         - level 2: a standard message, encrypted to a random pubkey
24      """
25      if stealthLevel == 2:  # Generate privacy-enhanced payload
26          # Generate a dummy privkey and derive the pubkey
27          dummyPubKeyHex = highlevelcrypto.privToPub(
28              hexlify(highlevelcrypto.randomBytes(32)))
29          # Generate a dummy message of random length
30          # (the smallest possible standard-formatted message is 234 bytes)
31          dummyMessage = highlevelcrypto.randomBytes(
32              helper_random.randomrandrange(234, 801))
33          # Encrypt the message using standard BM encryption (ECIES)
34          ackdata = highlevelcrypto.encrypt(dummyMessage, dummyPubKeyHex)
35          acktype = 2  # message
36          version = 1
37  
38      elif stealthLevel == 1:  # Basic privacy payload (random getpubkey)
39          ackdata = highlevelcrypto.randomBytes(32)
40          acktype = 0  # getpubkey
41          version = 4
42  
43      else:            # Minimum viable payload (non stealth)
44          ackdata = highlevelcrypto.randomBytes(32)
45          acktype = 2  # message
46          version = 1
47  
48      ackobject = pack('>I', acktype) + encodeVarint(
49          version) + encodeVarint(streamNumber) + ackdata
50  
51      return ackobject