diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index c1eb1d7..46ab38e 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,4 +1,91 @@
 [root]
 name = "advent_of_code"
 version = "0.1.0"
+dependencies = [
+ "rust-crypto 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "advapi32-sys"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "gcc"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "advapi32-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "kernel32-sys"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "libc"
+version = "0.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "libc"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "rand"
+version = "0.3.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "advapi32-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rust-crypto"
+version = "0.2.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "gcc 0.3.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-serialize 0.3.16 (registry+https://github.com/rust-lang/crates.io-index)",
+ "time 0.1.34 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rustc-serialize"
+version = "0.3.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "time"
+version = "0.1.34"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "kernel32-sys 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "winapi"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "winapi-build"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
 
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 83e72ab..ece5289 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -2,3 +2,6 @@
 name = "advent_of_code"
 version = "0.1.0"
 authors = ["Alpha Chen <alpha.chen@gmail.com>"]
+
+[dependencies]
+rust-crypto = "^0.2"
diff --git a/rust/input/day_04.txt b/rust/input/day_04.txt
new file mode 100644
index 0000000..73269d7
--- /dev/null
+++ b/rust/input/day_04.txt
@@ -0,0 +1 @@
+ckczppom
\ No newline at end of file
diff --git a/rust/src/day_04.rs b/rust/src/day_04.rs
new file mode 100644
index 0000000..9e7f2e6
--- /dev/null
+++ b/rust/src/day_04.rs
@@ -0,0 +1,42 @@
+use std::io;
+
+use crypto::md5::Md5;
+use crypto::digest::Digest;
+
+use day::Day;
+
+pub struct Day04 {
+    secret: String,
+}
+
+impl Day for Day04 {
+    fn new(input: String) -> Day04 {
+        Day04 { secret: input }
+    }
+
+    fn solve(&self) -> io::Result<i32> {
+        let mut md5 = Md5::new();
+        let key = self.secret.as_bytes();
+        let mut i = 0;
+        let mut out = [0; 16];
+        loop {
+            i += 1;
+
+            md5.input(key);
+            md5.input(i.to_string().as_bytes());
+            md5.result(&mut out);
+            if out[0] == 0 && out[1] == 0 && out[2] >> 4 == 0 {
+                break;
+            }
+            md5.reset();
+        }
+        Ok(i)
+    }
+}
+
+#[test]
+#[ignore]
+fn test_day04() {
+    let day = Day04::new("abcdef".to_string());
+    assert_eq!(609043, day.solve().unwrap());
+}
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 4c15b7f..6181391 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -1,3 +1,5 @@
+extern crate crypto;
+
 macro_rules! import_day {
     ( $( $d:ident ),* ) => {
         $(
@@ -10,4 +12,5 @@ macro_rules! import_day {
 import_day!(day,
             day_01,
             day_02,
-            day_03);
+            day_03,
+            day_04);
diff --git a/rust/src/main.rs b/rust/src/main.rs
index 3d7bd5e..8408257 100644
--- a/rust/src/main.rs
+++ b/rust/src/main.rs
@@ -19,7 +19,7 @@ fn read_input(filename: &str) -> Result<String, io::Error> {
 }
 
 fn main() {
-    let input = read_input("day_03").unwrap();
-    let day = Day03::new(input);
+    let input = read_input("day_04").unwrap();
+    let day = Day04::new(input);
     println!("{}", day.solve().unwrap());
 }