src/backup/crypt_config.rs - compute_digest: make it more secure

src/backup/crypt_config.rs

@@ -80,10 +80,9 @@ impl CryptConfig {
     /// chunk digest values do not clash with values computed for
     /// other sectret keys.
     pub fn compute_digest(&self, data: &[u8]) -> [u8; 32] {
-        // FIXME: use HMAC-SHA256 instead??
         let mut hasher = openssl::sha::Sha256::new();
-        hasher.update(&self.id_key);
         hasher.update(data);
+        hasher.update(&self.id_key); // at the end, to avoid length extensions attacks
         hasher.finish()
     }