Merge pull request #469 from lnbits/StepansFix

Makes lnurlpos work with latest lnurlpos.ino

lnbits/extensions/lnurlpos/lnurl.py

@@ -3,6 +3,12 @@ import hashlib
 from http import HTTPStatus
 from typing import Optional
 
+from embit import bech32
+from embit import compact
+import base64
+from io import BytesIO
+import hmac
+
 from fastapi import Request
 from fastapi.param_functions import Query
 from starlette.exceptions import HTTPException
@@ -18,39 +24,73 @@ from .crud import (
     update_lnurlpospayment,
 )
 
+def bech32_decode(bech):
+    """tweaked version of bech32_decode that ignores length limitations"""
+    if ((any(ord(x) < 33 or ord(x) > 126 for x in bech)) or
+            (bech.lower() != bech and bech.upper() != bech)):
+        return
+    bech = bech.lower()
+    pos = bech.rfind('1')
+    if pos < 1 or pos + 7 > len(bech):
+        return
+    if not all(x in bech32.CHARSET for x in bech[pos+1:]):
+        return
+    hrp = bech[:pos]
+    data = [bech32.CHARSET.find(x) for x in bech[pos+1:]]
+    encoding = bech32.bech32_verify_checksum(hrp, data)
+    if encoding is None:
+        return
+    return bytes(bech32.convertbits(data[:-6], 5, 8, False))
+
+def xor_decrypt(key, blob):
+    s = BytesIO(blob)
+    variant = s.read(1)[0]
+    if variant != 1:
+        raise RuntimeError("Not implemented")
+    # reading nonce
+    l = s.read(1)[0]
+    nonce = s.read(l)
+    if len(nonce) != l:
+        raise RuntimeError("Missing nonce bytes")
+    if l < 8:
+        raise RuntimeError("Nonce is too short")
+    # reading payload
+    l = s.read(1)[0]
+    payload = s.read(l)
+    if len(payload) > 32:
+        raise RuntimeError("Payload is too long for this encryption method")
+    if len(payload) != l:
+        raise RuntimeError("Missing payload bytes")
+    hmacval = s.read()
+    expected = hmac.new(key, b"Data:" + blob[:-len(hmacval)], digestmod="sha256").digest()
+    if len(hmacval) < 8:
+        raise RuntimeError("HMAC is too short")
+    if hmacval != expected[:len(hmacval)]:
+        raise RuntimeError("HMAC is invalid")
+    secret = hmac.new(key, b"Round secret:" + nonce, digestmod="sha256").digest()
+    payload = bytearray(payload)
+    for i in range(len(payload)):
+        payload[i] = payload[i] ^ secret[i]
+    s = BytesIO(payload)
+    pin = compact.read_from(s)
+    amount_in_cent = compact.read_from(s)
+    return pin, amount_in_cent
 
 @lnurlpos_ext.get(
-    "/api/v1/lnurl/{nonce}/{payload}/{pos_id}",
+    "/api/v1/lnurl/{pos_id}",
     status_code=HTTPStatus.OK,
-    name="lnurlpos.lnurl_response",
+    name="lnurlpos.lnurl_v1_params",
 )
-async def lnurl_response(
-    request: Request,
-    nonce: str = Query(None),
-    pos_id: str = Query(None),
-    payload: str = Query(None),
-):
-    return await handle_lnurl_firstrequest(
-        request, pos_id, nonce, payload, verify_checksum=False
-    )
-
-
-@lnurlpos_ext.get(
-    "/api/v2/lnurl/{pos_id}",
-    status_code=HTTPStatus.OK,
-    name="lnurlpos.lnurl_v2_params",
-)
-async def lnurl_v2_params(
+async def lnurl_v1_params(
     request: Request,
     pos_id: str = Query(None),
-    n: str = Query(None),
     p: str = Query(None),
 ):
-    return await handle_lnurl_firstrequest(request, pos_id, n, p, verify_checksum=True)
+    return await handle_lnurl_firstrequest(request, pos_id, p)
 
 
 async def handle_lnurl_firstrequest(
-    request: Request, pos_id: str, nonce: str, payload: str, verify_checksum: bool
+    request: Request, pos_id: str, payload: str
 ):
     pos = await get_lnurlpos(pos_id)
     if not pos:
@@ -59,53 +99,13 @@ async def handle_lnurl_firstrequest(
             "reason": f"lnurlpos {pos_id} not found on this server",
         }
 
-    try:
-        nonceb = bytes.fromhex(nonce)
-    except ValueError:
-        try:
-            nonce += "=" * ((4 - len(nonce) % 4) % 4)
-            nonceb = base64.urlsafe_b64decode(nonce)
-        except:
-            return {
-                "status": "ERROR",
-                "reason": f"Invalid hex or base64 nonce: {nonce}",
-            }
-
-    try:
-        payloadb = bytes.fromhex(payload)
-    except ValueError:
-        try:
-            payload += "=" * ((4 - len(payload) % 4) % 4)
-            payloadb = base64.urlsafe_b64decode(payload)
-        except:
-            return {
-                "status": "ERROR",
-                "reason": f"Invalid hex or base64 payload: {payload}",
-            }
-
-    # check payload and nonce sizes
-    if len(payloadb) != 8 or len(nonceb) != 8:
-        return {"status": "ERROR", "reason": "Expected 8 bytes"}
-
-    # verify hmac
-    if verify_checksum:
-        expected = hmac.new(
-            pos.key.encode(), payloadb[:-2], digestmod="sha256"
-        ).digest()
-        if expected[:2] != payloadb[-2:]:
-            return {"status": "ERROR", "reason": "Invalid HMAC"}
-
-    # decrypt
-    s = hmac.new(pos.key.encode(), nonceb, digestmod="sha256").digest()
-    res = bytearray(payloadb)
-    for i in range(len(res)):
-        res[i] = res[i] ^ s[i]
-
-    pin = int.from_bytes(res[0:2], "little")
-    amount = int.from_bytes(res[2:6], "little")
+    if len(payload) % 4 > 0:
+        payload += "="*(4-(len(payload)%4))
 
+    data = base64.urlsafe_b64decode(payload)
+    pin, amount_in_cent = xor_decrypt(pos.key.encode(), data)
     price_msat = (
-        await fiat_amount_as_satoshis(float(amount) / 100, pos.currency)
+        await fiat_amount_as_satoshis(float(amount_in_cent) / 100, pos.currency)
         if pos.currency != "sat"
         else amount
     ) * 1000
@@ -161,7 +161,7 @@ async def lnurl_callback(request: Request, paymentid: str = Query(None)):
         "successAction": {
             "tag": "url",
             "description": "Check the attached link",
-            "url": req.url_for("lnurlpos.displaypin", paymentid=paymentid),
+            "url": request.url_for("lnurlpos.displaypin", paymentid=paymentid),
         },
         "routes": [],
     }