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effective_go: fix up the description of cipher blocks and streams

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R=golang-dev, r, agl, dsymonds
CC=golang-dev
https://golang.org/cl/5374046
This commit is contained in:
Rob Pike 2011-11-09 14:40:49 -08:00
parent 217408abf3
commit a9aef26a55
2 changed files with 65 additions and 44 deletions
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56
doc/effective_go.html
View File

@ -1915,42 +1915,53 @@ the rest of the code is unaffected by the change of algorithm.
</p>
<p>
A similar approach allows the streaming cipher algorithms
in the <code>crypto/block</code> package to be
in the various <code>crypto</code> packages to be
separated from the block ciphers they chain together.
By analogy with the <code>bufio</code> package,
they wrap a <code>Cipher</code> interface
and return <code>hash.Hash</code>,
<code>io.Reader</code>, or <code>io.Writer</code>
interface values, not specific implementations.
The <code>Block</code> interface
in the <code>crypto/cipher</code>package specifies the
behavior of a block cipher, which provides encryption
of a single block of data.
Then, by analogy with the <code>bufio</code> package,
cipher packages that implement this interface
can be used to construct streaming ciphers, represented
by the <code>Stream</code> interface, without
knowing the details of the block encryption.
</p>
<p>
The interface to <code>crypto/block</code> includes:
The <code>crypto/cipher</code> interfaces look like this:
</p>
<pre>
type Cipher interface {
type Block interface {
BlockSize() int
Encrypt(src, dst []byte)
Decrypt(src, dst []byte)
}
// NewECBDecrypter returns a reader that reads data
// from r and decrypts it using c in electronic codebook (ECB) mode.
func NewECBDecrypter(c Cipher, r io.Reader) io.Reader
type Stream interface {
XORKeyStream(dst, src []byte)
}
</pre>
// NewCBCDecrypter returns a reader that reads data
// from r and decrypts it using c in cipher block chaining (CBC) mode
// with the initialization vector iv.
func NewCBCDecrypter(c Cipher, iv []byte, r io.Reader) io.Reader
<p>
Here's the definition of the counter mode (CTR) stream,
which turns a block cipher into a streaming cipher; notice
that the block cipher's details are abstracted away:
</p>
<pre>
// NewCTR returns a Stream that encrypts/decrypts using the given Block in
// counter mode. The length of iv must be the same as the Block's block size.
func NewCTR(block Block, iv []byte) Stream
</pre>
<p>
<code>NewECBDecrypter</code> and <code>NewCBCReader</code> apply not
<code>NewCTR</code> applies not
just to one specific encryption algorithm and data source but to any
implementation of the <code>Cipher</code> interface and any
<code>io.Reader</code>. Because they return <code>io.Reader</code>
interface values, replacing ECB
encryption with CBC encryption is a localized change. The constructor
implementation of the <code>Block</code> interface and any
<code>Stream</code>. Because they return
interface values, replacing CTR
encryption with other encryption modes is a localized change. The constructor
calls must be edited, but because the surrounding code must treat the result only
as an <code>io.Reader</code>, it won't notice the difference.
as a <code>Stream</code>, it won't notice the difference.
</p>
<h3 id="interface_methods">Interfaces and methods</h3>
@ -2930,8 +2941,7 @@ import (
&#34;text/template&#34;
)
var // Q=17, R=18
addr = flag.String(&#34;addr&#34;, &#34;:1718&#34;, &#34;http service address&#34;)
var addr = flag.String(&#34;addr&#34;, &#34;:1718&#34;, &#34;http service address&#34;) // Q=17, R=18
var templ = template.Must(template.New(&#34;qr&#34;).Parse(templateStr))

53
doc/effective_go.tmpl
View File

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