base-station: Simplify decryption.

base-station/software/src/radio.rs

@@ -107,36 +107,13 @@ fn radio_thread(updates: &mpsc::Sender<SensorUpdate>) -> Result<(), Error> {
             let mut payload = payload.as_ref().to_vec();
 
             let sensor_id = payload[0];
-            let mut salt = payload[0..8].to_vec();
 
             // Decrypt the package
             let key = [
                 0x9e, 0x37, 0x79, 0xb9, 0x9b, 0x97, 0x73, 0xe9, 0xb9, 0x79, 0x37, 0x9e, 0x6b, 0x69,
                 0x51, 0x56,
             ]; //TODO: define somewhere else
-               //decrypt(&key, &mut payload.as_mut_slice()[8..32]);
-
-            let mut position_in_buffer = 24;
-            let (mut previous_cipher_block, mut current_cipher_block) =
-                payload[position_in_buffer - 8..position_in_buffer + 8].split_at_mut(8);
-
-            loop {
-                decrypt(&key, current_cipher_block);
-
-                for i in 0..8 {
-                    current_cipher_block[i] ^= previous_cipher_block[i];
-                }
-
-                position_in_buffer -= 8;
-                if position_in_buffer == 0 {
-                    break;
-                }
-                info!("position_in_buffer = {}", position_in_buffer);
-                let blocks =
-                    payload[position_in_buffer - 8..position_in_buffer + 8].split_at_mut(8);
-                previous_cipher_block = blocks.0;
-                current_cipher_block = blocks.1;
-            }
+            decrypt_cbc(&key, &mut payload);
             info!("decrypted: {:x?}", payload);
 
             // Calculate the CRC
@@ -253,6 +230,22 @@ fn radio_thread(updates: &mpsc::Sender<SensorUpdate>) -> Result<(), Error> {
     }
 }
 
+fn decrypt_cbc(key: &[u8], data: &mut [u8]) {
+    let mut blocks = data.rchunks_mut(8).peekable();
+    loop {
+        let block = blocks.next().unwrap();
+        let prev_block = match blocks.peek() {
+            Some(b) => b,
+            None => break,
+        };
+        decrypt(&key, block);
+
+        for i in 0..8 {
+            block[i] ^= prev_block[i];
+        }
+    }
+}
+
 fn get_pin_number(c: char, n: u64) -> u64 {
     (c as u64 - 'A' as u64) * 32 + n
 }