diff --git a/2015/04/Cargo.lock b/2015/04/Cargo.lock
new file mode 100644
index 0000000..bdb450c
--- /dev/null
+++ b/2015/04/Cargo.lock
@@ -0,0 +1,81 @@
+[root]
+name = "04"
+version = "0.1.0"
+dependencies = [
+ "rust-crypto 0.2.36 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "gcc"
+version = "0.3.38"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "kernel32-sys"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "winapi 0.2.8 (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 = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "rand"
+version = "0.3.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.17 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rust-crypto"
+version = "0.2.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "gcc 0.3.38 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-serialize 0.3.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "time 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "rustc-serialize"
+version = "0.3.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "time"
+version = "0.1.35"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "winapi 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "winapi"
+version = "0.2.8"
+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"
+
+[metadata]
+"checksum gcc 0.3.38 (registry+https://github.com/rust-lang/crates.io-index)" = "553f11439bdefe755bf366b264820f1da70f3aaf3924e594b886beb9c831bcf5"
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+"checksum libc 0.2.17 (registry+https://github.com/rust-lang/crates.io-index)" = "044d1360593a78f5c8e5e710beccdc24ab71d1f01bc19a29bcacdba22e8475d8"
+"checksum rand 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)" = "022e0636ec2519ddae48154b028864bdce4eaf7d35226ab8e65c611be97b189d"
+"checksum rust-crypto 0.2.36 (registry+https://github.com/rust-lang/crates.io-index)" = "f76d05d3993fd5f4af9434e8e436db163a12a9d40e1a58a726f27a01dfd12a2a"
+"checksum rustc-serialize 0.3.21 (registry+https://github.com/rust-lang/crates.io-index)" = "bff9fc1c79f2dec76b253273d07682e94a978bd8f132ded071188122b2af9818"
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diff --git a/2015/04/Cargo.toml b/2015/04/Cargo.toml
new file mode 100644
index 0000000..daab903
--- /dev/null
+++ b/2015/04/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "04"
+version = "0.1.0"
+authors = ["logaritmisk <anders.e.olsson@gmail.com>"]
+
+[dependencies]
+rust-crypto = "^0.2"
diff --git a/2015/04/src/main.rs b/2015/04/src/main.rs
new file mode 100644
index 0000000..d10b19a
--- /dev/null
+++ b/2015/04/src/main.rs
@@ -0,0 +1,48 @@
+extern crate crypto;
+
+
+use std::u64;
+
+use crypto::md5::Md5;
+use crypto::digest::Digest;
+
+
+fn main() {
+    println!("{:?}", process("ckczppom", "000000"));
+}
+
+fn process(secret: &str, starts_with: &str) -> Option<u64> {
+    let mut md5 = Md5::new();
+
+    for i in 1..u64::MAX {
+        let input = format!("{}{}", secret, i);
+
+        md5.input(input.as_bytes());
+
+        let result = md5.result_str();
+
+        if result.starts_with(starts_with) {
+            return Some(i);
+        }
+
+        md5.reset();
+    }
+
+    None
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::process;
+
+    #[test]
+    fn example_01() {
+        assert_eq!(Some(609043), process("abcdef", "00000"));
+    }
+
+    #[test]
+    fn example_02() {
+        assert_eq!(Some(1048970), process("pqrstuv", "00000"));
+    }
+}