added nostr_decode_npub

nostr_core/core.c

@@ -421,7 +421,33 @@ int nostr_decode_nsec(const char* input, unsigned char* private_key) {
     return NOSTR_SUCCESS;
 }
 
-
+int nostr_decode_npub(const char* input, unsigned char* public_key) {
+    if (!input || !public_key) {
+        return NOSTR_ERROR_INVALID_INPUT;
+    }
+    
+    nostr_input_type_t type = nostr_detect_input_type(input);
+    
+    if (type == NOSTR_INPUT_NSEC_HEX) {  // Actually public key hex
+        if (nostr_hex_to_bytes(input, public_key, 32) != NOSTR_SUCCESS) {
+            return NOSTR_ERROR_INVALID_INPUT;
+        }
+    } else if (strncmp(input, "npub1", 4) == 0) {  // Bech32 npub
+        size_t decoded_len;
+        if (!bech32_decode(input, "npub", public_key, &decoded_len)) {
+            return NOSTR_ERROR_INVALID_INPUT;
+        }
+        if (decoded_len != 32) {
+            return NOSTR_ERROR_INVALID_INPUT;
+        }
+    } else {
+        return NOSTR_ERROR_INVALID_INPUT;
+    }
+    
+    // Validate the public key (could add nostr_ec_public_key_verify if it exists)
+    
+    return NOSTR_SUCCESS;
+}
 
 ////////////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////

nostr_core/nostr_core.h

@@ -318,7 +318,14 @@ nostr_input_type_t nostr_detect_input_type(const char* input);
  */
 int nostr_decode_nsec(const char* input, unsigned char* private_key);
 
-
+/**
+ * Validate and decode an npub (hex or bech32) to private key
+ * 
+ * @param input Input nsec string
+ * @param private_key Output buffer for private key (32 bytes)
+ * @return NOSTR_SUCCESS on success, error code on failure
+ */
+int nostr_decode_npub(const char* input, unsigned char* private_key);
 
 
 ////////////////////////////////////////////////////////////////////////////////