From 3f67f1f0ea40971a68ae416ae067a017b7560c16 Mon Sep 17 00:00:00 2001
From: scgbckbone <virgovica@gmail.com>
Date: Sun, 10 Jul 2022 10:38:05 +0200
Subject: [PATCH] BIP-85 passwords

---
 bip85/__init__.py         | 10 ++++++++++
 bip85/app.py              |  9 ++++++++-
 bip85/cli.py              | 10 ++++++++++
 bip85/tests/test_bip85.py | 20 ++++++++++++++++++++
 4 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/bip85/__init__.py b/bip85/__init__.py
index 2c033e1..610200e 100644
--- a/bip85/__init__.py
+++ b/bip85/__init__.py
@@ -25,6 +25,7 @@
 from pycoin.symbols.btc import network as BTC
 from pycoin.encoding.bytes32 import from_bytes_32, to_bytes_32
 import base58
+import base64
 
 
 class BIP85(object):
@@ -59,6 +60,15 @@ def bip32_xprv_to_hex(self, path, width, xprv_string):
         ent = self.bip32_xprv_to_entropy(path, xprv_string)
         return ent[0:width].hex()
 
+    def bip32_xprv_to_pwd(self, path, pwd_len, xprv_string):
+        # export entropy as hex
+        if not 20 <= pwd_len <= 86:
+            raise ValueError("'pwd_len' has to be in closed interval <20..86>")
+        path = self._decorate_path(path)
+        ent = self.bip32_xprv_to_entropy(path, xprv_string)
+        ent_b64 = base64.b64encode(ent).decode().strip()
+        return ent_b64[:pwd_len]
+
     def bip32_xprv_to_xprv(self, path, xprv_string):
         path = self._decorate_path(path)
         ent = self.bip32_xprv_to_entropy(path, xprv_string)
diff --git a/bip85/app.py b/bip85/app.py
index d76665e..cd65ab7 100644
--- a/bip85/app.py
+++ b/bip85/app.py
@@ -53,12 +53,19 @@ def wif(xprv_string, index):
 
 
 def hex(xprv_string, index, width):
-    # m/83696968'/128169p'/index'
+    # m/83696968'/128169p'/width'/index'
     bip85 = BIP85()
     path = f"83696968p/128169p/{width}p/{index}p"
     return bip85.bip32_xprv_to_hex(path, width, xprv_string)
 
 
+def pwd(xprv_string, index, pwd_len):
+    # m/83696968'/707764'/pwd_len'/index'
+    bip85 = BIP85()
+    path = f"83696968p/707764p/{pwd_len}p/{index}p"
+    return bip85.bip32_xprv_to_pwd(path, pwd_len, xprv_string)
+
+
 def xprv(xprv_string, index):
     # 83696968'/32'/index'
     bip85 = BIP85()
diff --git a/bip85/cli.py b/bip85/cli.py
index 645d60a..9b82310 100644
--- a/bip85/cli.py
+++ b/bip85/cli.py
@@ -66,6 +66,14 @@ def main():
                                 required=True,
                                 help='Number of bytes to generate')
     subparsers.add_parser('xprv', help='Derive an XPRV (master private key)')
+    app_pwd_parser = subparsers.add_parser('pwd',
+                                           help='Derive a password')
+    app_pwd_parser.add_argument('--pwd-len',
+                                type=int,
+                                choices=range(20,87),
+                                metavar="[20-86]",
+                                required=True,
+                                help='Desired password length')
     args = parser.parse_args()
     xprv = _get_xprv_from_args(args)
     print(f"Using master private key: {xprv}")
@@ -77,6 +85,8 @@ def main():
         print(app.hex(xprv, args.index, args.num_bytes))
     elif args.bip85_app == 'xprv':
         print(app.xprv(xprv, args.index))
+    elif args.bip85_app == "pwd":
+        print(app.pwd(xprv, args.index, args.pwd_len))
 
 
 if __name__ == "__main__":
diff --git a/bip85/tests/test_bip85.py b/bip85/tests/test_bip85.py
index c81ca35..ece6282 100644
--- a/bip85/tests/test_bip85.py
+++ b/bip85/tests/test_bip85.py
@@ -100,6 +100,26 @@ def test_hex(path, width, expect):
     bip85 = BIP85()
     assert bip85.bip32_xprv_to_hex(path, width, XPRV) == expect
 
+@pytest.mark.parametrize('path, pwd_len, expect', [
+        ("83696968'/707764'/20'/0'", 20, "RrH7uVI0XlpddCbiuYV+"),
+        ("83696968'/707764'/21'/0'", 21, "dKLoepugzdVJvdL56ogNV"),
+        ("83696968'/707764'/24'/0'", 24, "vtV6sdNQTKpuefUMOHOKwUp1"),
+        ("83696968'/707764'/32'/1234'", 32, "mBhJgXCJd6IpdOu1cc/D1wU+5sxj/1tK"),
+        ("83696968'/707764'/64'/1234'", 64, "HBqosVLBhKneX8ZCZgLdvmA8biOdUV2S/AteE5Rs8sMT0pfG3aItk/IrHGEpY9um"),
+        ("83696968'/707764'/86'/1234'", 86, "7n3VQ63qjgY6OJBQxqWYToNRfzzN5J8DwN1D8JqlZfnsF+1LdPXG3gkOXighX4iKyKip8nRIhVVVObh/G41F7g"),
+    ])
+def test_pwd(path, pwd_len, expect):
+    bip85 = BIP85()
+    assert bip85.bip32_xprv_to_pwd(path, pwd_len, XPRV) == expect
+
+def test_pwd_out_of_range():
+    bip85 = BIP85()
+    with pytest.raises(ValueError):
+        bip85.bip32_xprv_to_pwd("83696968'/707764'/87'/0'", 87, XPRV)
+
+    with pytest.raises(ValueError):
+        bip85.bip32_xprv_to_pwd("83696968'/707764'/19'/0'", 19, XPRV)
+
 def test_bipentropy_applications():
     assert app.bip39(XPRV, 'english', 18, 0) == \
            'near account window bike charge season chef number sketch tomorrow excuse sniff circle vital hockey outdoor supply token'