java - 静态机密作为字节 []、密钥还是字符串？

Question

我已经开始使用JJWT来处理我的服务器应用程序上的 JWT。

我的 JWT 机密将存储在resources文件夹中，我将使用类加载机密Properties。

JJWT提供了三种方式来对 JWT 进行签名，一种是 uses ，byte[] other usesString和 other uses Key：

JwtBuilder signWith(SignatureAlgorithm var1, byte[] var2);

JwtBuilder signWith(SignatureAlgorithm var1, String var2);

JwtBuilder signWith(SignatureAlgorithm var1, Key var2);

问题：关于安全、字符集和其他东西，我应该使用哪一个有什么建议吗？

有一段时间，我支持String，因为Properties返回 a String。

Answer 1

JJWT >= 0.10.0，signWith(SignatureAlgorithm var1, String var2)由于原始字符串和 Base64 编码字符串之间的混淆而被弃用：

/**
 * Signs the constructed JWT using the specified algorithm with the specified key, producing a JWS.
 *
 * <p>This is a convenience method: the string argument is first BASE64-decoded to a byte array and this resulting
 * byte array is used to invoke {@link #signWith(SignatureAlgorithm, byte[])}.</p>
 *
 * <h4>Deprecation Notice: Deprecated as of 0.10.0, will be removed in the 1.0 release.</h4>
 *
 * <p>This method has been deprecated because the {@code key} argument for this method can be confusing: keys for
 * cryptographic operations are always binary (byte arrays), and many people were confused as to how bytes were
 * obtained from the String argument.</p>
 *
 * <p>This method always expected a String argument that was effectively the same as the result of the following
 * (pseudocode):</p>
 *
 * <p>{@code String base64EncodedSecretKey = base64Encode(secretKeyBytes);}</p>
 *
 * <p>However, a non-trivial number of JJWT users were confused by the method signature and attempted to
 * use raw password strings as the key argument - for example {@code signWith(HS256, myPassword)} - which is
 * almost always incorrect for cryptographic hashes and can produce erroneous or insecure results.</p>
 *
 * <p>See this
 * <a href="https://stackoverflow.com/questions/40252903/static-secret-as-byte-key-or-string/40274325#40274325">
 * StackOverflow answer</a> explaining why raw (non-base64-encoded) strings are almost always incorrect for
 * signature operations.</p>
 *
 * <p>To perform the correct logic with base64EncodedSecretKey strings with JJWT >= 0.10.0, you may do this:
 * <pre><code>
 * byte[] keyBytes = {@link Decoders Decoders}.{@link Decoders#BASE64 BASE64}.{@link Decoder#decode(Object) decode(base64EncodedSecretKey)};
 * Key key = {@link Keys Keys}.{@link Keys#hmacShaKeyFor(byte[]) hmacShaKeyFor(keyBytes)};
 * jwtBuilder.signWith(key); //or {@link #signWith(Key, SignatureAlgorithm)}
 * </code></pre>
 * </p>
 *
 * <p>This method will be removed in the 1.0 release.</p>
 *
 * @param alg                    the JWS algorithm to use to digitally sign the JWT, thereby producing a JWS.
 * @param base64EncodedSecretKey the BASE64-encoded algorithm-specific signing key to use to digitally sign the
 *                               JWT.
 * @return the builder for method chaining.
 * @throws InvalidKeyException if the Key is insufficient or explicitly disallowed by the JWT specification as
 *                             described by {@link SignatureAlgorithm#forSigningKey(Key)}.
 * @deprecated as of 0.10.0: use {@link #signWith(Key)} or {@link #signWith(Key, SignatureAlgorithm)} instead.  This
 * method will be removed in the 1.0 release.
 */
JwtBuilder signWith(SignatureAlgorithm alg, String base64EncodedSecretKey);

此方法期望字符串参数是 Base64 编码的密钥字节数组。它不假定将通用字符串（例如用户密码）作为签名密钥。JJWT 假定使用 Base64 编码，因为如果您指定的字符串密码不是Base64 编码的，那么您可能使用了格式不正确或弱的密钥。

JWT JWA 规范要求HMAC 签名密钥的长度等于或大于签名字节数组长度。

这意味着：

| If you're signing with: | your key (byte array) length MUST be: |
| ----------------------- | ------------------------------------- |
| HMAC SHA 256            | >= 256 bits (32 bytes)                |
| HMAC SHA 384            | >= 384 bits (48 bytes)                |
| HMAC SHA 512            | >= 512 bits (64 bytes)                |

许多在线 JWT 网站和工具只是犯了这个明显的错误——它们让你认为你可以输入或使用任何旧字符串并且你很好。有些甚至用这个词预先填充密钥secret（显然是一个坏主意，甚至不符合规范，因为它太短了！）。

io.jsonwebtoken.security.Keys为了帮助您简化事情，JJWT 提供了一个实用程序来帮助您生成足够的安全随机密钥，这些密钥适用于通过类的secretKeyFor方法进行符合规范的签名。例如：

//creates a spec-compliant secure-random key:
SecretKey key = Keys.secretKeyFor(SignatureAlgorithm.HS256); //or HS384 or HS512

如果您想将生成的密钥存储为字符串，您可能可以对其进行 Base64 编码：

String base64Key = Encoders.BASE64.encode(key.getEncoded());

但请注意：生成的base64Key字符串不被认为可以安全地显示给任何人。Base64 编码不是加密 - 该值仍然需要保密。你如何做到这一点取决于你（加密它等）。

现在，当需要创建 JWS 时，您可以传入该base64Key值，JJWT 知道首先对其进行 base64 解码以获取实际字节，然后用于计算签名：

Jwts.builder()
    //...
    .signWith(SignatureAlgorithm.HS512, base64Key)
    .compact();

虽然您可以这样做，但由于原始字符串和 base64 编码字符串之间的歧义，不建议按照 JavaDoc 中的上述弃用通知。

因此，建议使用 JWT 构建器signWith(Key)或signWith(Key, SignatureAlgorithm)保证类型安全Key参数的方法。例如：

  Jwts.builder()
    //...
    .signWith(key) // or signWith(key, preferredSignatureAlgorithm)
    .compact();

signWith(Key)建议让 JJWT 根据您提供的密钥的强度找出可能的最强算法。 signWith(Key,SignatureAlgorithm)如果您不想要最强的算法，则允许您指定所需的算法。

这两种方法都将拒绝任何Key不符合最低 RFC 要求的内容。