# Go 中的密码学

通过网络传输的数据必须加密，以防止被 hacker（黑客）读取或篡改，并且保证发出的数据和收到的数据检验和一致。 鉴于 Go 母公司的业务，我们毫不惊讶地看到 Go 的标准库为该领域提供了超过 30 个的包：

* `hash` 包：实现了 `adler32`、`crc32`、`crc64` 和 `fnv` 校验；
* `crypto` 包：实现了其它的 hash 算法，比如 `md4`、`md5`、`sha1` 等。以及完整地实现了 `aes`、`blowfish`、`rc4`、`rsa`、`xtea` 等加密算法。

下面的示例用 `sha1` 和 `md5` 计算并输出了一些校验值。

示例 12.20 [hash\_sha1.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/examples/chapter_12/hash_sha1.go)：

```go
// hash_sha1.go
package main

import (
    "fmt"
    "crypto/sha1"
    "io"
    "log"
)

func main() {
    hasher := sha1.New()
    io.WriteString(hasher, "test")
    b := []byte{}
    fmt.Printf("Result: %x\n", hasher.Sum(b))
    fmt.Printf("Result: %d\n", hasher.Sum(b))
    //
    hasher.Reset()
    data := []byte("We shall overcome!")
    n, err := hasher.Write(data)
    if n!=len(data) || err!=nil {
        log.Printf("Hash write error: %v / %v", n, err)
    }
    checksum := hasher.Sum(b)
    fmt.Printf("Result: %x\n", checksum)
}
```

输出：

```
Result: a94a8fe5ccb19ba61c4c0873d391e987982fbbd3
Result: [169 74 143 229 204 177 155 166 28 76 8 115 211 145 233 135 152 47 187 211]
Result: e2222bfc59850bbb00a722e764a555603bb59b2a
```

通过调用 `sha1.New()` 创建了一个新的 `hash.Hash` 对象，用来计算 SHA1 校验值。`Hash` 类型实际上是一个接口，它实现了 `io.Writer` 接口：

```go
type Hash interface {
    // Write (via the embedded io.Writer interface) adds more data to the running hash.
    // It never returns an error.
    io.Writer

    // Sum appends the current hash to b and returns the resulting slice.
    // It does not change the underlying hash state.
    Sum(b []byte) []byte

    // Reset resets the Hash to its initial state.
    Reset()

    // Size returns the number of bytes Sum will return.
    Size() int

    // BlockSize returns the hash's underlying block size.
    // The Write method must be able to accept any amount
    // of data, but it may operate more efficiently if all writes
    // are a multiple of the block size.
    BlockSize() int
}
```

通过 io.WriteString 或 hasher.Write 将给定的 \[]byte 附加到当前的 `hash.Hash` 对象中。

**练习 12.9**：[hash\_md5.go](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/exercises/chapter_12/hash_md5.go)：

在示例 12.20 中检验 md5 算法。

## 链接

* [目录](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/directory.md)
* 上一节：[用 Gob 传输数据](/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/12.0/12.11.md)
* 下一章：[错误处理与测试](/the-way-to-go-zh-cn/di-san-bu-fen-go-gao-ji-bian-cheng/13.0.md)


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