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src/algos/cryptography/hashing.md

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+# 哈希
+
+### 计算文件的 SHA-256 摘要
+写入一些数据到文件中，然后使用 [digest::Context](https://briansmith.org/rustdoc/ring/digest/struct.Context.html) 来计算文件内容的 SHA-256 摘要 [digest::Digest](https://briansmith.org/rustdoc/ring/digest/struct.Digest.html)。
+
+```rust,editable
+# use error_chain::error_chain;
+use data_encoding::HEXUPPER;
+use ring::digest::{Context, Digest, SHA256};
+use std::fs::File;
+use std::io::{BufReader, Read, Write};
+
+# error_chain! {
+#    foreign_links {
+#        Io(std::io::Error);
+#        Decode(data_encoding::DecodeError);
+#    }
+# }
+
+fn sha256_digest<R: Read>(mut reader: R) -> Result<Digest> {
+    let mut context = Context::new(&SHA256);
+    let mut buffer = [0; 1024];
+
+    loop {
+        let count = reader.read(&mut buffer)?;
+        if count == 0 {
+            break;
+        }
+        context.update(&buffer[..count]);
+    }
+
+    Ok(context.finish())
+}
+
+fn main() -> Result<()> {
+    let path = "file.txt";
+
+    let mut output = File::create(path)?;
+    write!(output, "We will generate a digest of this text")?;
+
+    let input = File::open(path)?;
+    let reader = BufReader::new(input);
+    let digest = sha256_digest(reader)?;
+
+    println!("SHA-256 digest is {}", HEXUPPER.encode(digest.as_ref()));
+
+    Ok(())
+}
+```
+
+### 使用 HMAC 摘要来签名和验证消息
+使用 [ring::hmac](https://briansmith.org/rustdoc/ring/hmac/) 创建一个字符串签名并检查该签名的正确性。
+
+```rust,editable
+use ring::{hmac, rand};
+use ring::rand::SecureRandom;
+use ring::error::Unspecified;
+
+fn main() -> Result<(), Unspecified> {
+    let mut key_value = [0u8; 48];
+    let rng = rand::SystemRandom::new();
+    rng.fill(&mut key_value)?;
+    let key = hmac::Key::new(hmac::HMAC_SHA256, &key_value);
+
+    let message = "Legitimate and important message.";
+    let signature = hmac::sign(&key, message.as_bytes());
+    hmac::verify(&key, message.as_bytes(), signature.as_ref())?;
+
+    Ok(())
+}
+```