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effective_go: fix up the description of cipher blocks and streams
R=golang-dev, r, agl, dsymonds CC=golang-dev https://golang.org/cl/5374046
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@ -1915,42 +1915,53 @@ the rest of the code is unaffected by the change of algorithm.
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</p>
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<p>
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A similar approach allows the streaming cipher algorithms
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in the <code>crypto/block</code> package to be
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in the various <code>crypto</code> packages to be
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separated from the block ciphers they chain together.
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By analogy with the <code>bufio</code> package,
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they wrap a <code>Cipher</code> interface
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and return <code>hash.Hash</code>,
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<code>io.Reader</code>, or <code>io.Writer</code>
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interface values, not specific implementations.
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The <code>Block</code> interface
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in the <code>crypto/cipher</code>package specifies the
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behavior of a block cipher, which provides encryption
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of a single block of data.
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Then, by analogy with the <code>bufio</code> package,
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cipher packages that implement this interface
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can be used to construct streaming ciphers, represented
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by the <code>Stream</code> interface, without
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knowing the details of the block encryption.
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</p>
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<p>
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The interface to <code>crypto/block</code> includes:
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The <code>crypto/cipher</code> interfaces look like this:
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</p>
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<pre>
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type Cipher interface {
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type Block interface {
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BlockSize() int
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Encrypt(src, dst []byte)
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Decrypt(src, dst []byte)
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}
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// NewECBDecrypter returns a reader that reads data
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// from r and decrypts it using c in electronic codebook (ECB) mode.
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func NewECBDecrypter(c Cipher, r io.Reader) io.Reader
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type Stream interface {
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XORKeyStream(dst, src []byte)
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}
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</pre>
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// NewCBCDecrypter returns a reader that reads data
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// from r and decrypts it using c in cipher block chaining (CBC) mode
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// with the initialization vector iv.
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func NewCBCDecrypter(c Cipher, iv []byte, r io.Reader) io.Reader
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<p>
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Here's the definition of the counter mode (CTR) stream,
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which turns a block cipher into a streaming cipher; notice
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that the block cipher's details are abstracted away:
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</p>
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<pre>
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// NewCTR returns a Stream that encrypts/decrypts using the given Block in
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// counter mode. The length of iv must be the same as the Block's block size.
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func NewCTR(block Block, iv []byte) Stream
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</pre>
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<p>
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<code>NewECBDecrypter</code> and <code>NewCBCReader</code> apply not
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<code>NewCTR</code> applies not
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just to one specific encryption algorithm and data source but to any
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implementation of the <code>Cipher</code> interface and any
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<code>io.Reader</code>. Because they return <code>io.Reader</code>
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interface values, replacing ECB
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encryption with CBC encryption is a localized change. The constructor
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implementation of the <code>Block</code> interface and any
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<code>Stream</code>. Because they return
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interface values, replacing CTR
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encryption with other encryption modes is a localized change. The constructor
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calls must be edited, but because the surrounding code must treat the result only
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as an <code>io.Reader</code>, it won't notice the difference.
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as a <code>Stream</code>, it won't notice the difference.
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</p>
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<h3 id="interface_methods">Interfaces and methods</h3>
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@ -2930,8 +2941,7 @@ import (
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"text/template"
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)
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var // Q=17, R=18
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addr = flag.String("addr", ":1718", "http service address")
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var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18
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var templ = template.Must(template.New("qr").Parse(templateStr))
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@ -1853,42 +1853,53 @@ the rest of the code is unaffected by the change of algorithm.
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</p>
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<p>
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A similar approach allows the streaming cipher algorithms
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in the <code>crypto/block</code> package to be
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in the various <code>crypto</code> packages to be
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separated from the block ciphers they chain together.
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By analogy with the <code>bufio</code> package,
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they wrap a <code>Cipher</code> interface
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and return <code>hash.Hash</code>,
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<code>io.Reader</code>, or <code>io.Writer</code>
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interface values, not specific implementations.
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The <code>Block</code> interface
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in the <code>crypto/cipher</code>package specifies the
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behavior of a block cipher, which provides encryption
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of a single block of data.
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Then, by analogy with the <code>bufio</code> package,
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cipher packages that implement this interface
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can be used to construct streaming ciphers, represented
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by the <code>Stream</code> interface, without
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knowing the details of the block encryption.
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</p>
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<p>
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The interface to <code>crypto/block</code> includes:
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The <code>crypto/cipher</code> interfaces look like this:
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</p>
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<pre>
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type Cipher interface {
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type Block interface {
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BlockSize() int
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Encrypt(src, dst []byte)
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Decrypt(src, dst []byte)
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}
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// NewECBDecrypter returns a reader that reads data
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// from r and decrypts it using c in electronic codebook (ECB) mode.
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func NewECBDecrypter(c Cipher, r io.Reader) io.Reader
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type Stream interface {
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XORKeyStream(dst, src []byte)
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}
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</pre>
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// NewCBCDecrypter returns a reader that reads data
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// from r and decrypts it using c in cipher block chaining (CBC) mode
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// with the initialization vector iv.
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func NewCBCDecrypter(c Cipher, iv []byte, r io.Reader) io.Reader
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<p>
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Here's the definition of the counter mode (CTR) stream,
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which turns a block cipher into a streaming cipher; notice
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that the block cipher's details are abstracted away:
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</p>
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<pre>
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// NewCTR returns a Stream that encrypts/decrypts using the given Block in
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// counter mode. The length of iv must be the same as the Block's block size.
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func NewCTR(block Block, iv []byte) Stream
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</pre>
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<p>
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<code>NewECBDecrypter</code> and <code>NewCBCReader</code> apply not
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<code>NewCTR</code> applies not
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just to one specific encryption algorithm and data source but to any
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implementation of the <code>Cipher</code> interface and any
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<code>io.Reader</code>. Because they return <code>io.Reader</code>
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interface values, replacing ECB
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encryption with CBC encryption is a localized change. The constructor
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implementation of the <code>Block</code> interface and any
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<code>Stream</code>. Because they return
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interface values, replacing CTR
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encryption with other encryption modes is a localized change. The constructor
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calls must be edited, but because the surrounding code must treat the result only
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as an <code>io.Reader</code>, it won't notice the difference.
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as a <code>Stream</code>, it won't notice the difference.
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</p>
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<h3 id="interface_methods">Interfaces and methods</h3>
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