Merge pull request #580 from auth0/hmac-secret-length-notice

[SDK-3125] Updated documentation regarding HMAC Key length

README.md

@@ -113,7 +113,7 @@ You'll first need to create a `JWTVerifier` instance by calling `JWT.require()`
     ```java
     String token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXUyJ9.eyJpc3MiOiJhdXRoMCJ9.AbIJTDMFc7yUa5MhvcP03nJPyCPzZtQcGEp-zWfOkEE";
     try {
-        Algorithm algorithm = Algorithm.HMAC256("secret");
+        Algorithm algorithm = Algorithm.HMAC256("secret"); //use more secure key
         JWTVerifier verifier = JWT.require(algorithm)
             .withIssuer("auth0")
             .build(); //Reusable verifier instance
@@ -175,7 +175,7 @@ When using RSA or ECDSA algorithms and you just need to **sign** JWTs you can av
 
 ```java
 //HMAC
-Algorithm algorithmHS = Algorithm.HMAC256("secret");
+Algorithm algorithmHS = Algorithm.HMAC256("secret"); //use more secure key
 
 //RSA
 RSAPublicKey publicKey = //Get the key instance
@@ -185,9 +185,9 @@ Algorithm algorithmRS = Algorithm.RSA256(publicKey, privateKey);
 
 > Note: How you obtain or read keys is not in the scope of this library. For an example of how you might implement this, see [this gist](https://gist.github.com/lbalmaceda/9a0c7890c2965826c04119dcfb1a5469).
 
-##### HMAC Key Length and Security
+##### :key: HMAC Key Length and Security
 
-When using a Hash-based Message Authenticaton Code, e.g. HS256 or HS512, in order to comply with the strict requirements of the JSON Web Algorithms (JWA) specification (RFC7518), you **must** use a secret key which has the same (or larger) bit length as the size of the output hash. This is to avoid weakening the security strength of the authentication code (see NIST recommendations NIST SP 800-117). For example, when using HMAC256, the secret key length must be a minimum of 256 bits.
+When using a Hash-based Message Authentication Code, e.g. HS256 or HS512, in order to comply with the strict requirements of the JSON Web Algorithms (JWA) specification (RFC7518), you **must** use a secret key which has the same (or larger) bit length as the size of the output hash. This is to avoid weakening the security strength of the authentication code (see NIST recommendations NIST SP 800-117). For example, when using HMAC256, the secret key length must be a minimum of 256 bits.
 
 #### Using a KeyProvider:
 By using a `KeyProvider` you can change in runtime the key used either to verify the token signature or to sign a new token for RSA or ECDSA algorithms. This is achieved by implementing either `RSAKeyProvider` or `ECDSAKeyProvider` methods:

lib/src/main/java/com/auth0/jwt/algorithms/Algorithm.java

@@ -130,7 +130,9 @@ public static Algorithm RSA512(RSAKey key) throws IllegalArgumentException {
     /**
      * Creates a new Algorithm instance using HmacSHA256. Tokens specify this as "HS256".
      *
-     * @param secret the secret to use in the verify or signing instance.
+     * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 256 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC256 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */
@@ -142,6 +144,8 @@ public static Algorithm HMAC256(String secret) throws IllegalArgumentException {
      * Creates a new Algorithm instance using HmacSHA256. Tokens specify this as "HS256".
      *
      * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 256 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC256 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */
@@ -152,7 +156,9 @@ public static Algorithm HMAC256(byte[] secret) throws IllegalArgumentException {
     /**
      * Creates a new Algorithm instance using HmacSHA384. Tokens specify this as "HS384".
      *
-     * @param secret the secret to use in the verify or signing instance.
+     * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 384 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC384 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */
@@ -164,6 +170,8 @@ public static Algorithm HMAC384(String secret) throws IllegalArgumentException {
      * Creates a new Algorithm instance using HmacSHA384. Tokens specify this as "HS384".
      *
      * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 384 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC384 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */
@@ -174,7 +182,9 @@ public static Algorithm HMAC384(byte[] secret) throws IllegalArgumentException {
     /**
      * Creates a new Algorithm instance using HmacSHA512. Tokens specify this as "HS512".
      *
-     * @param secret the secret to use in the verify or signing instance.
+     * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 512 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC512 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */
@@ -186,6 +196,8 @@ public static Algorithm HMAC512(String secret) throws IllegalArgumentException {
      * Creates a new Algorithm instance using HmacSHA512. Tokens specify this as "HS512".
      *
      * @param secret the secret bytes to use in the verify or signing instance.
+     *               Ensure the length of the secret is at least 512 bit long
+     *               See <a href="https://github.com/auth0/java-jwt#hmac-key-length-and-security">HMAC Key Length and Security in README</a>
      * @return a valid HMAC512 Algorithm.
      * @throws IllegalArgumentException if the provided Secret is null.
      */