diff --git a/engine/shasum/shasum.go b/engine/shasum/shasum.go
new file mode 100644
index 00000000..3c6d504d
--- /dev/null
+++ b/engine/shasum/shasum.go
@@ -0,0 +1,72 @@
+package shasum
+
+import (
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/sha512"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// Check is a calculates and verifies a file checksum.
+// This supports the sha1, sha256 and sha512 values.
+func Check(in, checksum string) bool {
+	hash, size, _ := split(checksum)
+
+	// if a byte size is provided for the
+	// Yaml file it must match.
+	if size > 0 && int64(len(in)) != size {
+		return false
+	}
+
+	switch len(hash) {
+	case 64:
+		return sha256sum(in) == hash
+	case 128:
+		return sha512sum(in) == hash
+	case 40:
+		return sha1sum(in) == hash
+	case 0:
+		return true // if no checksum assume valid
+	}
+
+	return false
+}
+
+func sha1sum(in string) string {
+	h := sha1.New()
+	io.WriteString(h, in)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func sha256sum(in string) string {
+	h := sha256.New()
+	io.WriteString(h, in)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func sha512sum(in string) string {
+	h := sha512.New()
+	io.WriteString(h, in)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func split(in string) (string, int64, string) {
+	var hash string
+	var name string
+	var size int64
+
+	// the checksum might be split into multiple
+	// sections including the file size and name.
+	switch strings.Count(in, " ") {
+	case 1:
+		fmt.Sscanf(in, "%s %s", &hash, &name)
+	case 2:
+		fmt.Sscanf(in, "%s %d %s", &hash, &size, &name)
+	default:
+		hash = in
+	}
+
+	return hash, size, name
+}
diff --git a/engine/shasum/shasum_test.go b/engine/shasum/shasum_test.go
new file mode 100644
index 00000000..ff7c4ccc
--- /dev/null
+++ b/engine/shasum/shasum_test.go
@@ -0,0 +1,97 @@
+package shasum
+
+import (
+	"testing"
+
+	"github.com/franela/goblin"
+)
+
+func TestParse(t *testing.T) {
+
+	g := goblin.Goblin(t)
+	g.Describe("Shasum", func() {
+
+		g.It("Should parse the shasum string", func() {
+			hash, _, _ := split("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+			g.Assert(hash).Equal("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+		})
+
+		g.It("Should parse a two-part shasum string", func() {
+			hash, _, name := split("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15 .drone.yml")
+			g.Assert(hash).Equal("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+			g.Assert(name).Equal(".drone.yml")
+		})
+
+		g.It("Should parse a three-part shasum string", func() {
+			hash, size, name := split("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15 42 .drone.yml")
+			g.Assert(hash).Equal("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+			g.Assert(name).Equal(".drone.yml")
+			g.Assert(size).Equal(int64(42))
+		})
+
+		g.It("Should calc a sha1 sum", func() {
+			hash := sha1sum("foo\n")
+			g.Assert(hash).Equal("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+		})
+
+		g.It("Should calc a sha256 sum", func() {
+			hash := sha256sum("foo\n")
+			g.Assert(hash).Equal("b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c")
+		})
+
+		g.It("Should calc a sha512 sum", func() {
+			hash := sha512sum("foo\n")
+			g.Assert(hash).Equal("0cf9180a764aba863a67b6d72f0918bc131c6772642cb2dce5a34f0a702f9470ddc2bf125c12198b1995c233c34b4afd346c54a2334c350a948a51b6e8b4e6b6")
+		})
+
+		g.It("Should calc a sha1 sum", func() {
+			hash := sha1sum("foo\n")
+			g.Assert(hash).Equal("f1d2d2f924e986ac86fdf7b36c94bcdf32beec15")
+		})
+
+		g.It("Should validate sha1 sum with file size", func() {
+			ok := Check("foo\n", "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15 4 -")
+			g.Assert(ok).IsTrue()
+		})
+
+		g.It("Should validate sha256 sum with file size", func() {
+			ok := Check("foo\n", "b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c 4 -")
+			g.Assert(ok).IsTrue()
+		})
+
+		g.It("Should validate sha512 sum with file size", func() {
+			ok := Check("foo\n", "0cf9180a764aba863a67b6d72f0918bc131c6772642cb2dce5a34f0a702f9470ddc2bf125c12198b1995c233c34b4afd346c54a2334c350a948a51b6e8b4e6b6 4 -")
+			g.Assert(ok).IsTrue()
+		})
+
+		g.It("Should fail validation if incorrect sha1", func() {
+			ok := Check("bar\n", "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15 4 -")
+			g.Assert(ok).IsFalse()
+		})
+
+		g.It("Should fail validation if incorrect sha256", func() {
+			ok := Check("bar\n", "b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c 4 -")
+			g.Assert(ok).IsFalse()
+		})
+
+		g.It("Should fail validation if incorrect sha512", func() {
+			ok := Check("bar\n", "0cf9180a764aba863a67b6d72f0918bc131c6772642cb2dce5a34f0a702f9470ddc2bf125c12198b1995c233c34b4afd346c54a2334c350a948a51b6e8b4e6b6 4 -")
+			g.Assert(ok).IsFalse()
+		})
+
+		g.It("Should return false if file size mismatch", func() {
+			ok := Check("foo\n", "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15 12 -")
+			g.Assert(ok).IsFalse()
+		})
+
+		g.It("Should return false if invalid checksum string", func() {
+			ok := Check("foo\n", "f1d2d2f924e986ac86fdf7b36c94bcdf32beec15234")
+			g.Assert(ok).IsFalse()
+		})
+
+		g.It("Should return true if empty checksum", func() {
+			ok := Check("foo\n", "")
+			g.Assert(ok).IsTrue()
+		})
+	})
+}