Move relevant SRP-related code into another file

These functions are going to be used by all *_cloud_password methods

pyrogram/client/methods/password/utils.py

@@ -0,0 +1,103 @@
+# Pyrogram - Telegram MTProto API Client Library for Python
+# Copyright (C) 2017-2018 Dan Tès <https://github.com/delivrance>
+#
+# This file is part of Pyrogram.
+#
+# Pyrogram is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published
+# by the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Pyrogram is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Pyrogram.  If not, see <http://www.gnu.org/licenses/>.
+
+import hashlib
+import os
+
+from pyrogram.api import types
+
+
+def btoi(b: bytes) -> int:
+    return int.from_bytes(b, "big")
+
+
+def itob(i: int) -> bytes:
+    return i.to_bytes(256, "big")
+
+
+def sha256(data: bytes) -> bytes:
+    return hashlib.sha256(data).digest()
+
+
+def xor(a: bytes, b: bytes) -> bytes:
+    return bytes(i ^ j for i, j in zip(a, b))
+
+
+def compute_hash(algo: types.PasswordKdfAlgoSHA256SHA256PBKDF2HMACSHA512iter100000SHA256ModPow, password: str) -> bytes:
+    hash1 = sha256(algo.salt1 + password.encode() + algo.salt1)
+    hash2 = sha256(algo.salt2 + hash1 + algo.salt2)
+    hash3 = hashlib.pbkdf2_hmac("sha512", hash2, algo.salt1, 100000)
+
+    return sha256(algo.salt2 + hash3 + algo.salt2)
+
+
+def compute_check(r: types.account.Password, password: str) -> types.InputCheckPasswordSRP:
+    algo = r.current_algo
+
+    p_bytes = algo.p
+    p = btoi(algo.p)
+
+    g_bytes = itob(algo.g)
+    g = algo.g
+
+    B_bytes = r.srp_B
+    B = btoi(B_bytes)
+
+    srp_id = r.srp_id
+
+    x_bytes = compute_hash(algo, password)
+    x = btoi(x_bytes)
+
+    g_x = pow(g, x, p)
+
+    k_bytes = sha256(p_bytes + g_bytes)
+    k = btoi(k_bytes)
+
+    kg_x = (k * g_x) % p
+
+    while True:
+        a_bytes = os.urandom(256)
+        a = btoi(a_bytes)
+
+        A = pow(g, a, p)
+        A_bytes = itob(A)
+
+        u = btoi(sha256(A_bytes + B_bytes))
+
+        if u > 0:
+            break
+
+    g_b = (B - kg_x) % p
+
+    ux = u * x
+    a_ux = a + ux
+    S = pow(g_b, a_ux, p)
+    S_bytes = itob(S)
+
+    K_bytes = sha256(S_bytes)
+
+    M1_bytes = sha256(
+        xor(sha256(p_bytes), sha256(g_bytes))
+        + sha256(algo.salt1)
+        + sha256(algo.salt2)
+        + A_bytes
+        + B_bytes
+        + K_bytes
+    )
+
+    return types.InputCheckPasswordSRP(srp_id, A_bytes, M1_bytes)