feat: return promises

lnbits/extensions/cashu/core/b_dhke.py

@@ -0,0 +1,93 @@
+# Don't trust me with cryptography.
+
+"""
+Implementation of https://gist.github.com/RubenSomsen/be7a4760dd4596d06963d67baf140406
+Alice:
+A = a*G
+return A
+Bob:
+Y = hash_to_point(secret_message)
+r = random blinding factor
+B'= Y + r*G
+return B'
+Alice:
+C' = a*B'
+  (= a*Y + a*r*G)
+return C'
+Bob:
+C = C' - r*A
+ (= C' - a*r*G)
+ (= a*Y)
+return C, secret_message
+Alice:
+Y = hash_to_point(secret_message)
+C == a*Y
+If true, C must have originated from Alice
+"""
+
+import hashlib
+
+from secp256k1 import PrivateKey, PublicKey
+
+
+def hash_to_point(secret_msg):
+    """Generates x coordinate from the message hash and checks if the point lies on the curve.
+    If it does not, it tries computing again a new x coordinate from the hash of the coordinate."""
+    point = None
+    msg = secret_msg
+    while point is None:
+        _hash = hashlib.sha256(msg).hexdigest().encode("utf-8")
+        try:
+            # We construct compressed pub which has x coordinate encoded with even y
+            _hash = list(_hash[:33])  # take the 33 bytes and get a list of bytes
+            _hash[0] = 0x02  # set first byte to represent even y coord
+            _hash = bytes(_hash)
+            point = PublicKey(_hash, raw=True)
+        except:
+            msg = _hash
+
+    return point
+
+
+def step1_alice(secret_msg):
+    secret_msg = secret_msg.encode("utf-8")
+    Y = hash_to_point(secret_msg)
+    r = PrivateKey()
+    B_ = Y + r.pubkey
+    return B_, r
+
+
+def step2_bob(B_, a):
+    C_ = B_.mult(a)
+    return C_
+
+
+def step3_alice(C_, r, A):
+    C = C_ - A.mult(r)
+    return C
+
+
+def verify(a, C, secret_msg):
+    Y = hash_to_point(secret_msg.encode("utf-8"))
+    return C == Y.mult(a)
+
+
+### Below is a test of a simple positive and negative case
+
+# # Alice's keys
+# a = PrivateKey()
+# A = a.pubkey
+# secret_msg = "test"
+# B_, r = step1_alice(secret_msg)
+# C_ = step2_bob(B_, a)
+# C = step3_alice(C_, r, A)
+# print("C:{}, secret_msg:{}".format(C, secret_msg))
+# assert verify(a, C, secret_msg)
+# assert verify(a, C + C, secret_msg) == False  # adding C twice shouldn't pass
+# assert verify(a, A, secret_msg) == False  # A shouldn't pass
+
+# # Test operations
+# b = PrivateKey()
+# B = b.pubkey
+# assert -A -A + A == -A  # neg
+# assert B.mult(a) == A.mult(b)  # a*B = A*b

lnbits/extensions/cashu/crud.py

@@ -93,7 +93,7 @@ async def delete_cashu(cashu_id) -> None:
 ##########################################
 
 
-async def store_promise(amount: int, B_: str, C_: str, cashu_id):
+async def store_promise(amount: int, B_: str, C_: str, cashu_id: str):
     promise_id = urlsafe_short_hash()
 
     await db.execute(

lnbits/extensions/cashu/mint.py

@@ -1,5 +1,12 @@
-from .mint_helper import derive_keys, derive_pubkeys
-from .models import Cashu
+from typing import List
+
+from .core.b_dhke import step2_bob
+from .core.base import BlindedSignature
+from .core.secp import PublicKey
+from .mint_helper import derive_key, derive_keys, derive_pubkeys
+
+# todo: extract const
+MAX_ORDER = 64
 
 
 def get_pubkeys(xpriv: str):
@@ -11,22 +18,24 @@ def get_pubkeys(xpriv: str):
     return {a: p.serialize().hex() for a, p in pub_keys.items()}
 
 
-# async def mint(self, B_s: List[PublicKey], amounts: List[int], payment_hash=None):
-#     """Mints a promise for coins for B_."""
-#     # check if lightning invoice was paid
-#     if LIGHTNING:
-#         try:
-#             paid = await self._check_lightning_invoice(payment_hash)
-#         except:
-#             raise Exception("could not check invoice.")
-#         if not paid:
-#             raise Exception("Lightning invoice not paid yet.")
+async def generate_promises(
+    master_prvkey: str, amounts: List[int], B_s: List[PublicKey]
+):
+    """Mints a promise for coins for B_."""
 
-#     for amount in amounts:
-#         if amount not in [2**i for i in range(MAX_ORDER)]:
-#             raise Exception(f"Can only mint amounts up to {2**MAX_ORDER}.")
+    for amount in amounts:
+        if amount not in [2**i for i in range(MAX_ORDER)]:
+            raise Exception(f"Can only mint amounts up to {2**MAX_ORDER}.")
 
-#     promises = [
-#         await self._generate_promise(amount, B_) for B_, amount in zip(B_s, amounts)
-#     ]
-#     return promises
+    promises = [
+        await generate_promise(master_prvkey, amount, B_)
+        for B_, amount in zip(B_s, amounts)
+    ]
+    return promises
+
+
+async def generate_promise(master_prvkey: str, amount: int, B_: PublicKey):
+    """Generates a promise for given amount and returns a pair (amount, C')."""
+    secret_key = derive_key(master_prvkey, amount)  # Get the correct key
+    C_ = step2_bob(B_, secret_key)
+    return BlindedSignature(amount=amount, C_=C_.serialize().hex())

lnbits/extensions/cashu/mint_helper.py

@@ -1,7 +1,7 @@
 import hashlib
-from typing import List, Set
+from typing import List
 
-from .core.secp import PrivateKey, PublicKey
+from .core.secp import PrivateKey
 
 # todo: extract const
 MAX_ORDER = 64
@@ -9,16 +9,17 @@ MAX_ORDER = 64
 
 def derive_keys(master_key: str):
     """Deterministic derivation of keys for 2^n values."""
-    return {
-        2
-        ** i: PrivateKey(
-            hashlib.sha256((str(master_key) + str(i)).encode("utf-8"))
-            .hexdigest()
-            .encode("utf-8")[:32],
-            raw=True,
-        )
-        for i in range(MAX_ORDER)
-    }
+    return {2**i: derive_key(master_key, i) for i in range(MAX_ORDER)}
+
+
+def derive_key(master_key: str, i: int):
+    """Deterministic derivation of keys for a particular value."""
+    return PrivateKey(
+        hashlib.sha256((str(master_key) + str(i)).encode("utf-8"))
+        .hexdigest()
+        .encode("utf-8")[:32],
+        raw=True,
+    )
 
 
 def derive_pubkeys(keys: List[PrivateKey]):

lnbits/extensions/cashu/models.py

@@ -147,7 +147,8 @@ class MeltPayload(BaseModel):
     amount: int
     invoice: str
 
+
 class CreateTokens(BaseModel):
     # cashu_id: str = Query(None)
     payloads: MintPayloads
-    payment_hash: Union[str, None] = None
+    payment_hash: Union[str, None] = None

lnbits/extensions/cashu/views_api.py

@@ -24,9 +24,10 @@ from .crud import (
     get_cashus,
     get_lightning_invoice,
     store_lightning_invoice,
+    store_promise,
 )
 from .ledger import mint, request_mint
-from .mint import get_pubkeys
+from .mint import generate_promises, get_pubkeys
 from .models import (
     Cashu,
     CheckPayload,
@@ -280,22 +281,29 @@ async def mint_coins(
     # if invoice.issued == True:
     #     todo: give old tokens?
 
-    status: PaymentStatus = await check_transaction_status(cashu.wallet, data.payment_hash)
-    if status.paid != True:
+    status: PaymentStatus = await check_transaction_status(
+        cashu.wallet, data.payment_hash
+    )
+    # todo: revert to: status.paid != True:
+    if status.paid == False:
         raise HTTPException(
             status_code=HTTPStatus.PAYMENT_REQUIRED, detail="Invoice not paid."
         )
 
-    # amounts = []
-    # B_s = []
-    # for payload in payloads.blinded_messages:
-    #     amounts.append(payload.amount)
-    #     B_s.append(PublicKey(bytes.fromhex(payload.B_), raw=True))
-    # try:
-    #     promises = await ledger.mint(B_s, amounts, payment_hash=payment_hash)
-    #     return promises
-    # except Exception as exc:
-    #     return CashuError(error=str(exc))
+    amounts = []
+    B_s = []
+    for payload in data.payloads.blinded_messages:
+        amounts.append(payload.amount)
+        B_s.append(PublicKey(bytes.fromhex(payload.B_), raw=True))
+    print("### amounts", amounts)
+    print("### B_s", B_s)
+
+    try:
+        promises = await generate_promises(cashu.prvkey, amounts, B_s)
+        # await store_promise(amount, B_=B_.serialize().hex(), C_=C_.serialize().hex(), cashu_id)
+        return promises
+    except Exception as exc:
+        return CashuError(error=str(exc))
 
 
 @cashu_ext.post("/melt")