feat: add negative topups (#2835)

* feat: add negative topups
* remove topup dialog

---------

Co-authored-by: Vlad Stan <stan.v.vlad@gmail.com>

lnbits/utils/crypto.py

@@ -1,6 +1,6 @@
 import base64
 import getpass
-from hashlib import md5
+from hashlib import md5, pbkdf2_hmac, sha256
 
 from Cryptodome import Random
 from Cryptodome.Cipher import AES
@@ -8,6 +8,21 @@ from Cryptodome.Cipher import AES
 BLOCK_SIZE = 16
 
 
+def random_secret_and_hash() -> tuple[str, str]:
+    secret = Random.new().read(32)
+    return secret.hex(), sha256(secret).hexdigest()
+
+
+def fake_privkey(secret: str) -> str:
+    return pbkdf2_hmac(
+        "sha256",
+        secret.encode(),
+        b"FakeWallet",
+        2048,
+        32,
+    ).hex()
+
+
 class AESCipher:
     """This class is compatible with crypto-js/aes.js