diff --git a/core/lib/src/parser/signature.rs b/core/lib/src/parser/signature.rs
index 8582da01..efd780d4 100644
--- a/core/lib/src/parser/signature.rs
+++ b/core/lib/src/parser/signature.rs
@@ -31,13 +31,13 @@ use sha2::Sha256;
 ///     // NG
 /// }
 /// ```
-pub fn validate_signature(channel_secret: String, signature: String, body: String) -> bool {
+pub fn validate_signature(channel_secret: &str, signature: &str, body: &str) -> bool {
     type HmacSha256 = Hmac<Sha256>;
 
     let mut mac = HmacSha256::new_from_slice(channel_secret.as_bytes())
         .expect("HMAC can take key of any size");
     mac.update(body.as_bytes());
     let mut buf = String::new();
-    general_purpose::STANDARD.encode_string(&mac.finalize().into_bytes().to_vec(), &mut buf);
+    general_purpose::STANDARD.encode_string(mac.finalize().into_bytes(), &mut buf);
     buf == signature
 }
diff --git a/examples/actix_web_example/src/main.rs b/examples/actix_web_example/src/main.rs
index 350bdefa..57b79ccc 100644
--- a/examples/actix_web_example/src/main.rs
+++ b/examples/actix_web_example/src/main.rs
@@ -26,7 +26,7 @@ async fn callback(signature: Signature, bytes: web::Bytes) -> Result<HttpRespons
 
     let body: &str = &String::from_utf8(bytes.to_vec()).unwrap();
 
-    if !validate_signature(channel_secret.to_string(), signature.key, body.to_string()) {
+    if !validate_signature(channel_secret, &signature.key, body) {
         return Err(ErrorBadRequest("x-line-signature is invalid."));
     }
 
diff --git a/examples/rocket_example/src/main.rs b/examples/rocket_example/src/main.rs
index e782829c..f4f02866 100644
--- a/examples/rocket_example/src/main.rs
+++ b/examples/rocket_example/src/main.rs
@@ -26,7 +26,7 @@ async fn world(signature: Signature, body: String) -> (Status, &'static str) {
     println!("{signature:#?}");
     println!("{body:#?}");
 
-    if !validate_signature(channel_secret.to_string(), signature.key, body.clone()) {
+    if !validate_signature(channel_secret, &signature.key, &body) {
         return (Status::BadRequest, "x-line-signature is invalid.");
     }