payload almost done

payload/blockmode.go

@@ -0,0 +1,45 @@
+package payload
+
+import (
+	"crypto/cipher"
+	"errors"
+	"fmt"
+	"io"
+)
+
+type BlockStream func(block cipher.Block, iv []byte) cipher.Stream
+
+type BlockMode string
+
+const OFB BlockMode = "ofb"
+
+func (this BlockMode) GetEncryptorStream() (BlockStream, error) {
+	switch this {
+	case OFB:
+		return cipher.NewOFB, nil
+	default:
+		err := fmt.Sprintf("BlockMode '%s' is not available", this)
+		return nil, errors.New(err)
+	}
+
+}
+
+func createIV(b cipher.Block, rd io.Reader) ([]byte, error) {
+	ret := make([]byte, b.BlockSize())
+	if _, err := rd.Read(ret); err != nil {
+		return nil, err
+	}
+	return ret, nil
+}
+
+func (this BlockMode) GetCipherStream(block cipher.Block, rd io.Reader) (stream cipher.Stream, iv []byte, err error) {
+	iv, err = createIV(block, rd)
+	if err != nil {
+		return nil, nil, err
+	}
+	streamCreator, err := this.GetEncryptorStream()
+	if err != nil {
+		return nil, nil, err
+	}
+	return streamCreator(block, iv), iv, nil
+}