ring::pbkdf2的用法是，使用 PBKDF2 密钥派生函数pbkdf2::derive，哈希 腌制的密码。 用pbkdf2::verify验证哈希是否正确。 盐是用SecureRandom::fill生成的，它用安全生成的随机数，填充 salt 字节数组。

这个在哈希中加入字符串的方式称为“加盐”。其作用是让加盐后的哈希结果和没有加盐的结果不相同，在不同的应用情景中，这个处理可以增加额外的安全性。

extern crate ring;
extern crate data_encoding;

use data_encoding::HEXUPPER;
use ring::error::Unspecified;
use ring::rand::SecureRandom;
use ring::{digest, pbkdf2, rand};

fn main() -> Result<(), Unspecified> {
    const CREDENTIAL_LEN: usize = digest::SHA512_OUTPUT_LEN;
    const N_ITER: u32 = 100_000;
    let rng = rand::SystemRandom::new();

    let mut salt = [0u8; CREDENTIAL_LEN];
    rng.fill(&mut salt)?;

    let password = "Guess Me If You Can!";
    let mut pbkdf2_hash = [0u8; CREDENTIAL_LEN];
    pbkdf2::derive(
        &digest::SHA512,
        N_ITER,
        &salt,
        password.as_bytes(),
        &mut pbkdf2_hash,
    );
    println!("Salt: {}", HEXUPPER.encode(&salt));
    println!("PBKDF2 hash: {}", HEXUPPER.encode(&pbkdf2_hash));

    let should_succeed = pbkdf2::verify(
        &digest::SHA512,
        N_ITER,
        &salt,
        password.as_bytes(),
        &pbkdf2_hash,
    );
    let wrong_password = "Definitely not the correct password";
    let should_fail = pbkdf2::verify(
        &digest::SHA512,
        N_ITER,
        &salt,
        wrong_password.as_bytes(),
        &pbkdf2_hash,
    );

    assert!(should_succeed.is_ok());
    assert!(!should_fail.is_ok());

    Ok(())
}