HMAC 与密钥派生

Simply calculating hash_func(key + msg) to obtain a MAC (message authentication code) is considered insecure (see the details). It is recommended to use the HMAC algorithm instead, e.g. HMAC-SHA256 or HMAC-SHA3-512 or other secure MAC algorithm.

简单地计算 hash_func(key+msg)以获得 MAC（消息认证码）被认为是不安全的（请参阅详细信息）。建议改用 HMAC 算法，例如 HMAC-SHA256 或 HMAC-SHA3-512 或其他安全 MAC 算法。

什么是 HMAC？

HMAC = Hash-based Message Authentication Code (MAC code, calculated using a cryptographic hash function):

HMAC = Hash-based Message Authentication Code（MAC 码，使用加密哈希函数计算）：

HMAC(key, msg, hash_func) -> hash

The results MAC code is a message hash mixed with a secret key. It has the cryptographic properties of hashes: irreversible, collision resistant, etc.

结果 MAC 码是一个混合了密钥的消息哈希。它具有哈希的加密特性：不可逆、抗碰撞等。

The hash_func can be any cryptographic hash function like SHA-256, SHA-512, RIPEMD-160, SHA3-256 or BLAKE2s.

hash_func 可以是任何加密哈希函数，例如 SHA-256, SHA-512, RIPEMD-160, SHA3-256 或 BLAKE2s。

HMAC is used for message authenticity, message integrity and sometimes for key derivation.

HMAC 用于验证消息真实性，消息完整性，有时还用于密钥派生。

密钥派生函数（KDF）

Key derivation function (KDF) is a function which transforms a variable-length password to fixed-length key (sequence of bits):

密钥派生函数（Key Derivation Functions， KDF）是将可变长度密码转换为固定长度密钥（位序列）的函数：

function(password) -> key

As very simple KDF function, we can use SHA256: just hash the password. Don't do this, because it is insecure. Simple hashes are vulnerable to dictionary attacks.

作为非常简单的 KDF 函数，我们可以使用 SHA256：仅对密码进行哈希处理。不要这样做，因为它是不安全的。简单的哈希很容易受到字典攻击。

As more complicated KDF function, you can derive a password by calculating HMAC(salt, msg, SHA256) using some random value called "salt", which is stored along with the derived key and used later to derive the same key again from the password.

作为更复杂的 KDF 函数，我们可以通过使用一些称为“盐”的随机值来计算 HMAC（salt，msg，SHA256）来派生密钥，该随机值与派生密钥一起存储，用于以后再次从密码中派生相同的密钥。

Using HKDF (HMAC-based key derivation) for key derivation is less secure than modern KDFs, so experts recommend using stronger key derivation functions like PBKDF2, Bcrypt, Scrypt and Argon2. We shall discuss all these KDF functions later.

与现代 KDF 函数相比，使用 HKDF（基于 HMAC 的密钥派生）进行密钥派生的安全性较低，因此专家建议使用更强大的密钥派生函数，例如 PBKDF2， Bcrypt， Scrypt 和 Argon2。稍后我们将讨论这些 KDF 函数。

HMAC 计算——示例

To get a better idea of HMAC and how it is calculated, try this online tool: https://www.freeformatter.com/hmac-generator.html

要更好地了解 HMAC 及其计算方式，请尝试此在线工具：https://www.freeformatter.com/hmac-generator.html

Play with calculating HMAC('sample message', '12345', 'SHA256'):

尝试计算 HMAC('sample message', '12345', 'SHA256')：

HMAC('sample message', '12345', 'SHA256') =
  'ee40ca7bc90df844d2f5b5667b27361a2350fad99352d8a6ce061c69e41e5d32'

Try the above example yourself.

可自行尝试如上示例代码。