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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Output feedback (OFB) mode.
// OFB converts a block cipher into a stream cipher by
// repeatedly encrypting an initialization vector and
// xoring the resulting stream of data with the input.
// See NIST SP 800-38A, pp 13-15
package block
import (
"fmt"
"io"
)
type ofbStream struct {
c Cipher
iv []byte
}
func newOFBStream(c Cipher, iv []byte) *ofbStream {
x := new(ofbStream)
x.c = c
n := len(iv)
if n != c.BlockSize() {
panic(fmt.Sprintln("crypto/block: newOFBStream: invalid iv size", n, "!=", c.BlockSize()))
}
x.iv = dup(iv)
return x
}
func (x *ofbStream) Next() []byte {
x.c.Encrypt(x.iv, x.iv)
return x.iv
}
// NewOFBReader returns a reader that reads data from r, decrypts (or encrypts)
// it using c in output feedback (OFB) mode with the initialization vector iv.
// The returned Reader does not buffer and has no block size.
// In OFB mode, encryption and decryption are the same operation:
// an OFB reader applied to an encrypted stream produces a decrypted
// stream and vice versa.
func NewOFBReader(c Cipher, iv []byte, r io.Reader) io.Reader {
return newXorReader(newOFBStream(c, iv), r)
}
// NewOFBWriter returns a writer that encrypts (or decrypts) data using c
// in cipher feedback (OFB) mode with the initialization vector iv
// and writes the encrypted data to w.
// The returned Writer does not buffer and has no block size.
// In OFB mode, encryption and decryption are the same operation:
// an OFB writer applied to an decrypted stream produces an encrypted
// stream and vice versa.
func NewOFBWriter(c Cipher, iv []byte, w io.Writer) io.Writer {
return newXorWriter(newOFBStream(c, iv), w)
}
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