diff --git a/src/crypto/mod.rs b/src/crypto/mod.rs
index fa422be..ea3271e 100644
--- a/src/crypto/mod.rs
+++ b/src/crypto/mod.rs
@@ -13,6 +13,9 @@ pub trait PSOCipher {
     fn encrypt(&mut self, data: &Vec<u8>) -> Result<Vec<u8>, CipherError>;
     fn decrypt(&mut self, data: &Vec<u8>) -> Result<Vec<u8>, CipherError>;
     fn header_size(&self) -> usize;
+    fn block_size(&self) -> usize {
+        self.header_size()
+    }
 }