diff --git a/Cargo.lock b/Cargo.lock
index 07686dd..b2daae0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -7,9 +7,11 @@ name = "aoc"
 version = "0.1.0"
 dependencies = [
  "dotenv",
+ "hex-literal",
  "itertools",
  "pico-args",
  "reqwest",
+ "rust-crypto",
 ]
 
 [[package]]
@@ -130,6 +132,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "fuchsia-cprng"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
+
 [[package]]
 name = "futures-channel"
 version = "0.3.25"
@@ -178,6 +186,12 @@ dependencies = [
  "slab",
 ]
 
+[[package]]
+name = "gcc"
+version = "0.3.55"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f5f3913fa0bfe7ee1fd8248b6b9f42a5af4b9d65ec2dd2c3c26132b950ecfc2"
+
 [[package]]
 name = "h2"
 version = "0.3.15"
@@ -212,6 +226,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "hex-literal"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ebdb29d2ea9ed0083cd8cece49bbd968021bd99b0849edb4a9a7ee0fdf6a4e0"
+
 [[package]]
 name = "http"
 version = "0.2.8"
@@ -383,7 +403,7 @@ checksum = "e5d732bc30207a6423068df043e3d02e0735b155ad7ce1a6f76fe2baa5b158de"
 dependencies = [
  "libc",
  "log",
- "wasi",
+ "wasi 0.11.0+wasi-snapshot-preview1",
  "windows-sys 0.42.0",
 ]
 
@@ -514,6 +534,53 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand"
+version = "0.3.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "64ac302d8f83c0c1974bf758f6b041c6c8ada916fbb44a609158ca8b064cc76c"
+dependencies = [
+ "libc",
+ "rand 0.4.6",
+]
+
+[[package]]
+name = "rand"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "552840b97013b1a26992c11eac34bdd778e464601a4c2054b5f0bff7c6761293"
+dependencies = [
+ "fuchsia-cprng",
+ "libc",
+ "rand_core 0.3.1",
+ "rdrand",
+ "winapi",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a6fdeb83b075e8266dcc8762c22776f6877a63111121f5f8c7411e5be7eed4b"
+dependencies = [
+ "rand_core 0.4.2",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c33a3c44ca05fa6f1807d8e6743f3824e8509beca625669633be0acbdf509dc"
+
+[[package]]
+name = "rdrand"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "678054eb77286b51581ba43620cc911abf02758c91f93f479767aed0f90458b2"
+dependencies = [
+ "rand_core 0.3.1",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.2.16"
@@ -569,6 +636,25 @@ dependencies = [
  "winreg",
 ]
 
+[[package]]
+name = "rust-crypto"
+version = "0.2.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f76d05d3993fd5f4af9434e8e436db163a12a9d40e1a58a726f27a01dfd12a2a"
+dependencies = [
+ "gcc",
+ "libc",
+ "rand 0.3.23",
+ "rustc-serialize",
+ "time",
+]
+
+[[package]]
+name = "rustc-serialize"
+version = "0.3.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dcf128d1287d2ea9d80910b5f1120d0b8eede3fbf1abe91c40d39ea7d51e6fda"
+
 [[package]]
 name = "ryu"
 version = "1.0.11"
@@ -681,6 +767,17 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "time"
+version = "0.1.45"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b797afad3f312d1c66a56d11d0316f916356d11bd158fbc6ca6389ff6bf805a"
+dependencies = [
+ "libc",
+ "wasi 0.10.0+wasi-snapshot-preview1",
+ "winapi",
+]
+
 [[package]]
 name = "tinyvec"
 version = "1.6.0"
@@ -817,6 +914,12 @@ dependencies = [
  "try-lock",
 ]
 
+[[package]]
+name = "wasi"
+version = "0.10.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a143597ca7c7793eff794def352d41792a93c481eb1042423ff7ff72ba2c31f"
+
 [[package]]
 name = "wasi"
 version = "0.11.0+wasi-snapshot-preview1"
diff --git a/Cargo.toml b/Cargo.toml
index d2a904a..84a005b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,9 +8,9 @@ default-run = "aoc"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-# framework
 dotenv = "0.15.0"
+hex-literal = "0.3.4"
 itertools = "0.10.5"
 pico-args = "0.5.0"
 reqwest = { version = "0.11.13", features = ["blocking"] }
-# for solving
+rust-crypto = "0.2.36"
diff --git a/src/bin/04.rs b/src/bin/04.rs
new file mode 100644
index 000000000..52a2bda
--- /dev/null
+++ b/src/bin/04.rs
@@ -0,0 +1,57 @@
+use crypto::digest::Digest;
+use crypto::md5::Md5;
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let key = input.trim().as_bytes();
+    let mut hasher = Md5::new();
+    for x in 0..std::u64::MAX {
+        hasher.input(key);
+        hasher.input(x.to_string().as_bytes());
+
+        let mut output = [0; 16];
+        hasher.result(&mut output);
+
+        let first_five = output[0] as u32 + output[1] as u32 + (output[2] >> 4) as u32;
+        if first_five == 0 {
+            return Some(x as u32);
+        }
+        hasher.reset();
+    }
+    None
+}
+pub fn part_two(input: &str) -> Option<u32> {
+    let key = input.trim().as_bytes();
+    let mut hasher = Md5::new();
+    for x in 0..std::u64::MAX {
+        hasher.input(key);
+        hasher.input(x.to_string().as_bytes());
+
+        let mut output = [0; 16];
+        hasher.result(&mut output);
+
+        if output.starts_with(&[0,0,0]) { return Some(x as u32)}
+        hasher.reset();
+    }
+    None
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 4);
+    aoc::solve!(1, part_one, input);
+    aoc::solve!(2, part_two, input);
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        // let input = aoc::read_file("test_inputs", 4);
+        let input = "abcdef";
+        assert_eq!(part_one(&input), Some(609043));
+    }
+    #[test]
+    fn test_part_two() {
+        // let input = aoc::read_file("test_inputs", 4);
+        // let input = "abcdef";
+        // assert_eq!(part_two(&input), None);
+    }
+}