Merge pull request #1 from xian-network/extend_crypto

Extend `crypto` with `key_is_valid` function to check address

docs/concepts/crypto.md

@@ -1,15 +1,35 @@
 ## Crypto Standard Library
 
-In this example, the verify_signature function is an exported function in a Xian smart contract. It takes a verification key (vk), a message (msg), and a signature (signature). It uses the verify function from the crypto module to check if the signature is valid for the given message and verification key. The result (True or False) is then returned. This can be used to ensure data integrity and authenticity in transactions within the smart contract environment.
+The `crypto` module uses the `PyNaCl` library under the hood, employing the `Ed25519` signature scheme. The module consists of the following functions
 
-This module uses the `PyNaCl` library under the hood, employing the `Ed25519` signature scheme.
+### verify_signature
+
+It checks if the signature is valid for the given message and verification key. The result (True or False) is then returned. This can be used to ensure data integrity and authenticity in transactions within the smart contract environment.
+
+How to use it in a contract:
 
 ```python
 @export
 def verify_signature(vk: str, msg: str, signature: str):
-    # Use the verify function to check if the signature is valid for the given message and verification key
+    # Check if the signature is valid for the given message and verification key
     is_valid = crypto.verify(vk, msg, signature)
 
+    # Return the result of the verification
+    return is_valid
+```
+
+### key_is_valid
+
+It checks if the provided key (address) is valid or not. The result (True or False) is then returned.
+
+How to use it in a contract:
+
+```python
+@export
+def verify_address(address: str):
+    # Check if the given address is a valid Ed25519 key
+    is_valid = key_is_valid(address)
+
     # Return the result of the verification
     return is_valid
 ```