2 files changed, 63 insertions, 0 deletions
diff --git a/executables/hex_checksum-v2.py b/executables/hex_checksum-v2.py
new file mode 100644
index 0000000..71409f1
--- /dev/null
+++ b/executables/hex_checksum-v2.py
@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+import sys
+
+def compute_psa_checksum(data: bytes) -> bytes:
+    var_e = 0x0000  # Correct seed from firmware logic
+    for i in range(len(data)):
+        var_e ^= (data[i] + i) & 0xFFFF
+    return var_e.to_bytes(2, 'big')  # 2-byte checksum, big-endian
+
+def add_checksum(hexstring: str) -> str:
+    try:
+        data = bytes.fromhex(hexstring.strip())
+    except ValueError:
+        return "Invalid hex input!"
+    checksum = compute_psa_checksum(data)
+    return (data + checksum).hex()
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        print("Usage: ./hex_checksum.py <hexstring_without_checksum>")
+        sys.exit(1)
+    result = add_checksum(sys.argv[1])
+    print(result)
diff --git a/executables/hex_checksum.py b/executables/hex_checksum.py
new file mode 100644
index 0000000..72bb7b6
--- /dev/null
+++ b/executables/hex_checksum.py
@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+import sys
+
+"""
+PSA Checksum Calculator
+
+This script calculates the 2-byte checksum used in PSA multicast protocol messages.
+The checksum algorithm is based on reverse-engineered firmware behavior.
+
+How it works:
+-------------
+- Initialize a 16-bit value `var_e` to 0x0000
+- For each byte in the payload:
+    - Add the byte's index to its value (i.e., byte + index)
+    - XOR the result into `var_e`
+- The result is a 2-byte checksum (big endian: high byte first, low byte second)
+
+This checksum is appended to the payload to form a valid message.
+"""
+
+def compute_psa_checksum(data: bytes) -> bytes:
+    var_e = 0x0000
+    for i in range(len(data)):
+        var_e ^= (data[i] + i) & 0xFFFF
+    return var_e.to_bytes(2, 'big')
+
+def add_checksum(hexstring: str) -> str:
+    try:
+        data = bytes.fromhex(hexstring.strip())
+    except ValueError:
+        return "Invalid hex input!"
+    checksum = compute_psa_checksum(data)
+    return (data + checksum).hex()
+
+if __name__ == "__main__":
+    if len(sys.argv) != 2:
+        print("Usage: ./hex_checksum.py <hexstring_without_checksum>")
+        sys.exit(1)
+    result = add_checksum(sys.argv[1])
+    print(result)