Add util package with a DeHex function

util/util.go

@@ -0,0 +1,13 @@
+// package util provides small utility functions that make it easier to express common things
+package util
+
+import "encoding/hex"
+
+// DeHex decodes a hexadecimal string into a byte slice. Panics if the string is invalid.
+func DeHex(s string) []byte {
+	decoded, err := hex.DecodeString(s)
+	if err != nil {
+		panic("invalid hex string")
+	}
+	return decoded
+}

util/util_test.go

@@ -0,0 +1,25 @@
+package util_test
+
+import (
+	"testing"
+
+	"git.omicron.one/playground/cryptography/util"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDeHex(t *testing.T) {
+	b := util.DeHex("")
+	assert.NotNil(t, b)
+	assert.Len(t, b, 0)
+
+	b = util.DeHex("deadbeef")
+	assert.NotNil(t, b)
+	assert.Equal(t, []byte("\xde\xad\xbe\xef"), b)
+
+	assert.PanicsWithValue(t, "invalid hex string", func() {
+		util.DeHex("dead serious this is not a hex string")
+	})
+	assert.PanicsWithValue(t, "invalid hex string", func() {
+		util.DeHex("deada55")
+	})
+}