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pay.py
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pay.py
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# Payment proving system
#
# {(F,G,H),S,C,K,K_der,K_div,Q_0,Q_1,Q_2,v' ; k |
# K = k*Q_0,
# K_der = k*Q_1,
# K_div = k*F,
# S = H_ser(K_der)F + Q_2,
# C = SymDec(H_aead_val(K_der),v')G + H_val(K_der)H
# }
# Also require that memo decryption succeeds under the key H_aead_memo(K_der), that the view tag is correct, and that the diversifier assertion holds for K_div
import address
import coin
from dumb25519 import Point, Scalar, hash_to_scalar, random_scalar
import schnorr
import transcript
import util
class PayParameters:
def __init__(self,F,G,H,value_bytes):
if not isinstance(F,Point):
raise TypeError('Bad type for parameter F!')
if not isinstance(G,Point):
raise TypeError('Bad type for parameter G!')
if not isinstance(H,Point):
raise TypeError('Bad type for parameter H!')
if not isinstance(value_bytes,int) or value_bytes < 1:
raise ValueError('Bad type or value for parameter value_bytes!')
self.F = F
self.G = G
self.H = H
self.value_bytes = value_bytes
class PayStatement:
def __init__(self,params,context,coin_,K_der,K_div,public):
if not isinstance(params,PayParameters):
raise TypeError('Bad type for parameters!')
if not isinstance(coin_,coin.Coin):
raise TypeError('Bad type for pay statement coin!')
if not isinstance(K_der,Point):
raise TypeError('Bad type for pay statement input K_der!')
if not isinstance(K_div,Point):
raise TypeError('Bad type for pay statement input K_div!')
if not isinstance(public,address.PublicAddress):
raise TypeError('Bad type for pay statement public address!')
self.F = params.F
self.G = params.G
self.H = params.H
self.value_bytes = params.value_bytes
self.context = context
self.coin = coin_
self.K_der = K_der
self.K_div = K_div
self.public = public
class PayWitness:
def __init__(self,k):
if not isinstance(k,Scalar):
raise TypeError('Bad type for pay witness k!')
self.k = k
class PayProof:
def __init__(self,A1,A2,A3,t):
if not isinstance(A1,Point):
raise TypeError('Bad type for pay proof element A1!')
if not isinstance(A2,Point):
raise TypeError('Bad type for pay proof element A2!')
if not isinstance(A3,Point):
raise TypeError('Bad type for pay proof element A3!')
if not isinstance(t,Scalar):
raise TypeError('Bad type for pay proof element t!')
self.A1 = A1
self.A2 = A2
self.A3 = A3
self.t = t
def challenge(statement,A1,A2,A3):
if not isinstance(statement,PayStatement):
raise TypeError('Bad type for pay statement!')
if not isinstance(A1,Point):
raise TypeError('Bad type for challenge input A1!')
if not isinstance(A2,Point):
raise TypeError('Bad type for challenge input A2!')
if not isinstance(A3,Point):
raise TypeError('Bad type for challenge input A3!')
tr = transcript.Transcript('Pay proof')
tr.update(statement.F)
tr.update(statement.G)
tr.update(statement.H)
tr.update(statement.value_bytes)
tr.update(statement.context)
tr.update(statement.coin.S)
tr.update(statement.coin.C)
tr.update(statement.coin.K)
tr.update(statement.coin.enc)
tr.update(statement.coin.view_tag)
tr.update(statement.K_der)
tr.update(statement.K_div)
tr.update(statement.public.Q0)
tr.update(statement.public.Q1)
tr.update(statement.public.Q2)
tr.update(A1)
tr.update(A2)
tr.update(A3)
return tr.challenge()
def prove(statement,witness):
if not isinstance(statement,PayStatement):
raise TypeError('Bad type for pay statement!')
if not isinstance(witness,PayWitness):
raise TypeError('Bad type for pay witness!')
# Check the statement validity
if not statement.coin.K == witness.k*statement.public.Q0:
raise ArithmeticError('Invalid pay statement!')
if not statement.K_der == witness.k*statement.public.Q1:
raise ArithmeticError('Invalid pay statement!')
if not statement.K_div == witness.k*statement.F:
raise ArithmeticError('Invalid pay statement!')
if not statement.coin.S == hash_to_scalar('ser',statement.K_der)*statement.F + statement.public.Q2:
raise ArithmeticError('Invalid pay statement!')
if util.view_tag(statement.K_der) != statement.coin.view_tag:
raise ArithmeticError('Invalid pay statement!')
# Decrypt recipient data
aead_key = hash_to_scalar('aead',statement.K_der)
data_bytes = util.aead_decrypt(aead_key,'Spend recipient data',statement.coin.enc)
if data_bytes is not None:
value = int.from_bytes(data_bytes[:statement.value_bytes],'little')
else:
raise ArithmeticError('Bad recipient data!')
if not statement.coin.C == Scalar(value)*statement.G + hash_to_scalar('val',statement.K_der)*statement.H:
raise ArithmeticError('Invalid pay statement!')
r = random_scalar()
A1 = r*statement.public.Q0
A2 = r*statement.public.Q1
A3 = r*statement.F
c = challenge(statement,A1,A2,A3)
t = r + c*witness.k
return PayProof(A1,A2,A3,t)
def verify(statement,proof):
if not isinstance(statement,PayStatement):
raise TypeError('Bad type for pay statement!')
if not isinstance(proof,PayProof):
raise TypeError('Bad type for pay proof!')
c = challenge(statement,proof.A1,proof.A2,proof.A3)
if not proof.A1 + c*statement.coin.K == proof.t*statement.public.Q0:
raise ArithmeticError('Failed pay verification!')
if not proof.A2 + c*statement.K_der == proof.t*statement.public.Q1:
raise ArithmeticError('Failed pay verification!')
if not proof.A3 + c*statement.K_div == proof.t*statement.F:
raise ArithmeticError('Failed pay verification!')
# Test view tag
if util.view_tag(statement.K_der) != statement.coin.view_tag:
raise ArithmeticError('Failed pay verification!')
# Decrypt recipient data
aead_key = hash_to_scalar('aead',statement.K_der)
data_bytes = util.aead_decrypt(aead_key,'Spend recipient data',statement.coin.enc)
if data_bytes is not None:
value = int.from_bytes(data_bytes[:statement.value_bytes],'little')
else:
raise ArithmeticError('Bad recipient data!')
if not statement.coin.C == Scalar(value)*statement.G + hash_to_scalar('val',statement.K_der)*statement.H:
raise ArithmeticError('Failed pay verification!')
# Check diversifier
try:
schnorr.verify(
schnorr.SchnorrStatement(schnorr.SchnorrParameters(statement.F),statement.K_div),
statement.coin.janus
)
except:
raise ArithmeticError('Failed pay verification!')
# Test serial number and value commitments
if not statement.coin.S == hash_to_scalar('ser',statement.K_der)*statement.F + statement.public.Q2:
raise ArithmeticError('Failed pay verification!')
if not statement.coin.C == Scalar(value)*statement.G + hash_to_scalar('val',statement.K_der)*statement.H:
raise ArithmeticError('Failed pay verification!')