diff --git a/day04/day04.go b/day04/day04.go
new file mode 100644
index 0000000..36ac4f9
--- /dev/null
+++ b/day04/day04.go
@@ -0,0 +1,38 @@
+package day04
+
+import (
+	"aoc2015/aoclib"
+	"crypto/md5"
+	"encoding/hex"
+	"strconv"
+	"strings"
+)
+
+func findMd5SumStartsWith(secretStart string, start string) int {
+	var secret string
+	var md5sum [16]byte
+	counter := 0
+
+	for true {
+		secret = secretStart + strconv.Itoa(counter)
+		md5sum = md5.Sum([]byte(secret))
+		if strings.HasPrefix(hex.EncodeToString(md5sum[:]), start) {
+			return counter
+		}
+		counter++
+	}
+
+	return -1
+}
+
+func Part1(puzzle aoclib.Puzzle) interface{} {
+	secretStart := puzzle.GetInputArray()[0]
+
+	return findMd5SumStartsWith(secretStart, "00000")
+}
+
+func Part2(puzzle aoclib.Puzzle) interface{} {
+	secretStart := puzzle.GetInputArray()[0]
+
+	return findMd5SumStartsWith(secretStart, "000000")
+}
diff --git a/inputs/4 b/inputs/4
new file mode 100644
index 0000000..922d9e6
--- /dev/null
+++ b/inputs/4
@@ -0,0 +1 @@
+bgvyzdsv
\ No newline at end of file
diff --git a/inputs/4_test b/inputs/4_test
new file mode 100644
index 0000000..d96dc95
--- /dev/null
+++ b/inputs/4_test
@@ -0,0 +1 @@
+abcdef
\ No newline at end of file
diff --git a/main.go b/main.go
index 98ddbbd..05cf3a3 100644
--- a/main.go
+++ b/main.go
@@ -5,6 +5,7 @@ import (
 	"aoc2015/day01"
 	"aoc2015/day02"
 	"aoc2015/day03"
+	"aoc2015/day04"
 	"flag"
 	"fmt"
 	"os"
@@ -30,6 +31,9 @@ func initDayFunctions() {
 	dayFunctions[3] = make(map[int]func(puzzle aoclib.Puzzle) interface{})
 	dayFunctions[3][1] = day03.Part1
 	dayFunctions[3][2] = day03.Part2
+	dayFunctions[4] = make(map[int]func(puzzle aoclib.Puzzle) interface{})
+	dayFunctions[4][1] = day04.Part1
+	dayFunctions[4][2] = day04.Part2
 }
 
 func execute(thisDay int) {