diff --git a/payload/block.go b/payload/block.go
new file mode 100644
index 0000000..594970a
--- /dev/null
+++ b/payload/block.go
@@ -0,0 +1,46 @@
+package payload
+
+import (
+	"crypto"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/sha512"
+	"errors"
+	"io"
+)
+
+var _ = sha512.New
+
+type Block string
+
+const AES256 Block = "aes256"
+
+func hash512BytesOfData(h crypto.Hash, data io.Reader) ([]byte, error) {
+	if !h.Available() {
+		return nil, errors.New("unavailable hash function ")
+	}
+	hf := h.New()
+	if _, err := io.CopyN(hf, data, 512); err != nil {
+		return nil, err
+	}
+	return hf.Sum(nil), nil
+}
+
+func createRandomKey(lengthInBits int, rd io.Reader) ([]byte, error) {
+	if ret, err := hash512BytesOfData(crypto.SHA512, rd); err != nil {
+		return nil, err
+	} else if lengthInBits > len(ret)*8 {
+		return nil, errors.New("asked too long key.")
+	} else {
+		return ret[0 : lengthInBits/8], nil
+	}
+}
+
+func (this Block) CreateBlock(rd io.Reader) (cipher.Block, error) {
+	var err error
+	key := make([]byte, 256/8)
+	if _, err = rd.Read(key); err != nil {
+		return nil, err
+	}
+	return aes.NewCipher(key)
+}
diff --git a/payload/block_test.go b/payload/block_test.go
new file mode 100644
index 0000000..c0fc72f
--- /dev/null
+++ b/payload/block_test.go
@@ -0,0 +1,37 @@
+package payload
+
+import (
+	"crypto"
+	"github.com/didiercrunch/ecrypto/helper"
+	"testing"
+)
+
+func TestCreateBlock(t *testing.T) {
+	random := helper.NewMockRandomReader()
+	if block, err := AES256.CreateBlock(random); err != nil {
+		t.Error(err)
+	} else {
+		_ = block
+	}
+}
+
+func Testhash512BytesOfData(t *testing.T) {
+	if _, err := hash512BytesOfData(crypto.MD5, helper.NewMockRandomReader()); err == nil {
+		t.Error("should never allow MD5 hash")
+	}
+	rd := helper.NewMockRandomReader()
+	if rd, err := hash512BytesOfData(crypto.SHA512, rd); err != nil {
+		t.Error(err)
+	} else if len(rd) != 512/8 {
+		t.Fail()
+	}
+}
+
+func TestCreateRandomKey(t *testing.T) {
+	if key, err := createRandomKey(128, helper.NewMockRandomReader()); err != nil {
+		t.Error(err)
+	} else if len(key) != 128/8 {
+		t.Error("bad key length.  Expected 128 found ", len(key)*8)
+	}
+
+}