diff --git a/src/hash/md5.rs b/src/hash/md5.rs
index 66af360..c342b26 100644
--- a/src/hash/md5.rs
+++ b/src/hash/md5.rs
@@ -74,6 +74,7 @@ pub struct Md5 {
     buffer: [u8; Self::BLOCK_LEN],
     state: [u32; 4],
     len: usize,      // in bytes.
+    offset: usize,
 }
 
 impl Md5 {
@@ -86,88 +87,69 @@ impl Md5 {
             buffer: [0u8; Self::BLOCK_LEN],
             state: INITIAL_STATE,
             len: 0,
+            offset: 0,
         }
     }
 
     pub fn update(&mut self, data: &[u8]) {
-        // TODO:
-        // Unlike Sha1 and Sha2, the length value in MD5 is defined as
-        // the length of the message mod 2^64 - ie: integer overflow is OK.
-        if data.len() == 0 {
-            return ();
-        }
-
-        let mut n = self.len % Self::BLOCK_LEN;
-        if n != 0 {
-            let mut i = 0usize;
-            loop {
-                if n == 64 || i >= data.len() {
-                    break;
-                }
-                self.buffer[n] = data[i];
-                n += 1;
+        let mut i = 0usize;
+        while i < data.len() {
+            if self.offset < Self::BLOCK_LEN {
+                self.buffer[self.offset] = data[i];
+                self.offset += 1;
                 i += 1;
-                self.len += 1;
             }
-
-            if self.len % Self::BLOCK_LEN != 0 {
-                return ();
-            } else {
+            
+            if self.offset == Self::BLOCK_LEN {
                 transform(&mut self.state, &self.buffer);
-
-                let data = &data[i..];
-                if data.len() > 0 {
-                    return self.update(data);
-                }
-            }
-        }
-
-        if data.len() < 64 {
-            self.buffer[..data.len()].copy_from_slice(data);
-            self.len += data.len();
-        } else if data.len() == 64 {
-            transform(&mut self.state, data);
-            self.len += 64;
-        } else if data.len() > 64 {
-            let blocks = data.len() / 64;
-            for i in 0..blocks {
-                transform(&mut self.state, &data[i*64..i*64+64]);
-                self.len += 64;
-            }
-            let data = &data[blocks*64..];
-            if data.len() > 0 {
-                self.buffer[..data.len()].copy_from_slice(data);
-                self.len += data.len();
+                self.offset = 0;
+                self.len += Self::BLOCK_LEN;
             }
-        } else {
-            unreachable!()
         }
     }
 
     pub fn finalize(mut self) -> [u8; Self::DIGEST_LEN] {
-        // last_block
-        let len_bits = u64::try_from(self.len).unwrap() * 8;
-        let n = self.len % Self::BLOCK_LEN;
-        if n == 0 {
-            let mut block = [0u8; 64];
-            block[0] = 0x80;
-            block[56..].copy_from_slice(&len_bits.to_le_bytes());
-            transform(&mut self.state, &block);
-        } else {
-            self.buffer[n] = 0x80;
-            for i in n+1..64 {
-                self.buffer[i] = 0;
-            }
-            if 64 - n - 1 >= 8 {
-                self.buffer[56..].copy_from_slice(&len_bits.to_le_bytes());
-                transform(&mut self.state, &self.buffer);
-            } else {
-                transform(&mut self.state, &self.buffer);
-                let mut block = [0u8; 64];
-                block[56..].copy_from_slice(&len_bits.to_le_bytes());
-                transform(&mut self.state, &block);
-            }
-        }
+        let mlen = self.len + self.offset;  // in bytes
+        let mlen_bits = mlen * 8;           // in bits
+
+        let plen_bits = 512 - (mlen_bits + 64 + 1) % 512 + 1; // pad len, in bits
+        assert_eq!(plen_bits % 8, 0);
+        let plen = plen_bits / 8; // pad len, in bytes
+
+        // NOTE: MLEN + PLEN + MLEN_OCTETS (the length of the message before the padding bits were added)
+        let dlen = mlen + plen + 8;
+
+        assert_eq!(dlen % Self::BLOCK_LEN, 0);
+        assert!(plen > 1);
+
+        let mut padding_block: [u8; Self::BLOCK_LEN * 2] = [
+            0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+            0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
+
+        ];
+
+        let mlen_octets = u64::try_from(mlen_bits).unwrap();
+        padding_block[plen..plen + 8].copy_from_slice(&mlen_octets.to_le_bytes());
+        
+        let data = &padding_block[..plen + 8];
+        self.update(data);
+
+        assert_eq!(self.offset, 0);
 
         let mut output = [0u8; Self::DIGEST_LEN];
         output[ 0.. 4].copy_from_slice(&self.state[0].to_le_bytes());
@@ -447,4 +429,17 @@ fn test_md5_long_message() {
     let msg = vec![b'a'; 1000_000];
     let digest = [119, 7, 214, 174, 78, 2, 124, 112, 238, 162, 169, 53, 194, 41, 111, 33];
     assert_eq!(Md5::oneshot(&msg), digest);
-}
\ No newline at end of file
+}
+
+#[test]
+fn test_md5_oneshot() {
+    let mut m1 = Md5::new();
+    m1.update(&hex::decode("4b01a2d762fada9ede4d1034a13dc69c").unwrap());
+    m1.update(&hex::decode("496d616b65746869735f4c6f6e6750617373506872617365466f725f7361666574795f323031395f30393238405f4021").unwrap());
+    let h1 = m1.finalize();
+
+    let h2 = Md5::oneshot(&hex::decode("4b01a2d762fada9ede4d1034a13dc69c\
+496d616b65746869735f4c6f6e6750617373506872617365466f725f7361666574795f323031395f30393238405f4021").unwrap());
+
+    assert_eq!(h1, h2);
+}