diff --git a/src/sm2/ecc.rs b/src/sm2/ecc.rs
index beb4ad0..952ef82 100644
--- a/src/sm2/ecc.rs
+++ b/src/sm2/ecc.rs
@@ -485,6 +485,7 @@ impl EccCtx {
         ret
     }
 
+    #[allow(clippy::result_unit_err)]
     pub fn bytes_to_point(&self, b: &[u8]) -> Result<Point, ()> {
         let ctx = &self.fctx;
 
diff --git a/src/sm2/field.rs b/src/sm2/field.rs
index 879ae35..05e5bea 100644
--- a/src/sm2/field.rs
+++ b/src/sm2/field.rs
@@ -239,6 +239,7 @@ impl FieldCtx {
     }
 
     // Square root of a field element
+    #[allow(clippy::result_unit_err)]
     pub fn sqrt(&self, g: &FieldElem) -> Result<FieldElem, ()> {
         // p = 4 * u + 3
         // u = u + 1
diff --git a/src/sm2/signature.rs b/src/sm2/signature.rs
index e7d56a9..aa3fbe0 100644
--- a/src/sm2/signature.rs
+++ b/src/sm2/signature.rs
@@ -48,6 +48,7 @@ impl Signature {
         Ok(Signature { r, s })
     }
 
+    #[allow(clippy::result_unit_err)]
     pub fn der_decode_raw(buf: &[u8]) -> Result<Signature, ()> {
         if buf[0] != 0x02 {
             return Err(());
@@ -303,6 +304,7 @@ impl SigCtx {
         curve.mul(&sk, &curve.generator())
     }
 
+    #[allow(clippy::result_unit_err)]
     pub fn load_pubkey(&self, buf: &[u8]) -> Result<Point, ()> {
         self.curve.bytes_to_point(buf)
     }
@@ -311,6 +313,7 @@ impl SigCtx {
         self.curve.point_to_bytes(p, compress)
     }
 
+    #[allow(clippy::result_unit_err)]
     pub fn load_seckey(&self, buf: &[u8]) -> Result<BigUint, ()> {
         if buf.len() != 32 {
             return Err(());
diff --git a/src/sm4/cipher_mode.rs b/src/sm4/cipher_mode.rs
index 82f2eaa..4fbabc8 100644
--- a/src/sm4/cipher_mode.rs
+++ b/src/sm4/cipher_mode.rs
@@ -199,9 +199,7 @@ impl SM4CipherMode {
             let ct = block_xor(&vec_buf, &data[i * 16..i * 16 + 16]);
             let enc = self.cipher.encrypt(&ct);
 
-            for j in enc.iter() {
-                out.push(*j);
-            }
+            out.extend_from_slice(&enc);
             vec_buf = enc;
         }
 
@@ -211,18 +209,20 @@ impl SM4CipherMode {
 
             let ct = block_xor(&vec_buf, &last_block);
             let enc = self.cipher.encrypt(&ct);
-
-            for j in enc.iter() {
-                out.push(*j);
-            }
+            out.extend_from_slice(&enc);
+        } else {
+            let ff_padding = block_xor(&vec_buf, &[0x10; 16]);
+            let enc = self.cipher.encrypt(&ff_padding);
+            out.extend_from_slice(&enc);
         }
 
         out
     }
 
     fn cbc_decrypt(&self, data: &[u8], iv: &[u8]) -> Vec<u8> {
-        let block_num = data.len() / 16;
-        assert_eq!(data.len() % 16, 0);
+        let data_len = data.len();
+        let block_num = data_len / 16;
+        assert_eq!(data_len % 16, 0);
 
         let mut out: Vec<u8> = Vec::new();
         let mut vec_buf = [0; 16];
@@ -239,6 +239,10 @@ impl SM4CipherMode {
             vec_buf.copy_from_slice(&data[i * 16..i * 16 + 16]);
         }
 
+        let last_u8 = out[data_len - 1];
+        assert!(last_u8 <= 0x10 && last_u8 != 0);
+        out.resize(data_len - last_u8 as usize, 0);
+
         out
     }
 }
@@ -284,17 +288,17 @@ mod tests {
 
         let cmode = SM4CipherMode::new(&key, mode);
 
-        let pt = rand_data(16);
+        let pt = rand_data(10);
         let ct = cmode.encrypt(&pt[..], &iv);
         let new_pt = cmode.decrypt(&ct[..], &iv);
         assert_eq!(pt, new_pt);
 
-        let pt = rand_data(256);
+        let pt = rand_data(100);
         let ct = cmode.encrypt(&pt[..], &iv);
         let new_pt = cmode.decrypt(&ct[..], &iv);
         assert_eq!(pt, new_pt);
 
-        let pt = rand_data(4096);
+        let pt = rand_data(1000);
         let ct = cmode.encrypt(&pt[..], &iv);
         let new_pt = cmode.decrypt(&ct[..], &iv);
         assert_eq!(pt, new_pt);