diff --git a/src/sha/mod.rs b/src/sha/mod.rs
index 6435940..66c0d42 100644
--- a/src/sha/mod.rs
+++ b/src/sha/mod.rs
@@ -29,32 +29,28 @@ fn ssig1(x: u32) -> u32 {
     return ret;
 }
 
-fn pad_message(message: String) -> Vec<u32> {
-    let mut msg_bytes = message.as_bytes().to_vec();
-    let l = (msg_bytes.len() as u64) * 8;
+fn pad_message(msg: String) -> Vec<u32> {
+    let l = (msg.len() as u64) << 3;
+    let k = ((448u64.wrapping_sub((l + 8) % 512) % 512) >> 3) as usize;
 
-    msg_bytes.push(0x80);
+    let mut result_u8 = Vec::with_capacity(msg.len() + 1 + k + std::mem::size_of::<u64>());
 
-    let k = (448u64.wrapping_sub((l + 8) % 512)) % 512;
-    let k_bytes = k / 8;
+    result_u8.extend(msg.as_bytes());
+    result_u8.push(0x80);
+    result_u8.resize(result_u8.len() + k, 0u8);
+    result_u8.extend(&l.to_be_bytes());
 
-    let padding = vec![0u8; k_bytes as usize];
+    let mut result_u32 = Vec::with_capacity(result_u8.len() / 4); // Allocate the right size for u32 vector
 
-    msg_bytes.extend(padding);
-
-    msg_bytes.extend(&l.to_be_bytes());
-
-    let mut u32_vec = Vec::with_capacity(msg_bytes.len() / 4); // Allocate the right size for u32 vector
-
-    for chunk in msg_bytes.chunks(4) {
+    for chunk in result_u8.chunks(4) {
         let value = (chunk[0] as u32) << 24
             | (chunk[1] as u32) << 16
             | (chunk[2] as u32) << 8
             | (chunk[3] as u32);
-        u32_vec.push(value);
+        result_u32.push(value);
     }
 
-    return u32_vec;
+    return result_u32;
 }
 //////////// END HELPER FUNCTIONS /////////////