Mar 23, 2017 Brute Forcing HS256 is Possible: The Importance of Using Strong Keys in Signing JWTs. Cracking a JWT signed with weak keys is possible via brute force attacks. Learn how Auth0 protects against such attacks and alternative JWT signing methods provided.
The simplest kind of JSON Web Encryption (JWE) is directencryption with a symmetricAES key, hence the algorithm designation dir. Sender and recipient mustshare the same secret key, established by some out-of-band mechanism, unlessyou have a use case where the plain text is encrypted to self. Wireshark wpa pre shared key generator.
If you need public (asymmetric) key encryption, check out the available RSA andECDH algorithms for JWE.
Direct encryption works with any of the six standard available contentencryption algorithms (set by the 'enc' JWE header parameter). These aregrouped into two classes authenticated encryption withAES/CBC/HMAC/SHA andauthenticated encryption with AES/GCM.
The AES key length must match the expected for the selected JWE encryption. Ifthat condition isn't met the library will throw a JOSE exception whenencryption is attempted.
The required AES key length for a particular JWE encryption method can also beobtained programmatically:
Example direct encryption with AES GCM using a symmetric 128 bit key:
Important!
Don't forget to refer to the security considerations on key lifetimes insection 8.2 and AES GCM insection 8.4 of the JSON WebAlgorithm (JWA) spec when using direct encryption.
JSON Web Keys (JWK) can be easilygenerated with the help of the Nimbus JOSE+JWT library:
Cryptographic keys can also be generated in some other environment and thenconverted into JWK format. Here is an example howto import a key generated with OpenSSL.
You can also check out the command line JWK generator by JustinRicher built with this library.
RSA key pair
The only required parameter to generate an RSA key pair is the key length,which should be at least 2048 bits. There is an alternative constructor in caseyou need to generate weak keys.
The JWK format allows the key to be decorated with metadata. An important pieceof metadata is the key ID ('kid'), for key identification in databases andenabling key rollover. The usage parameter ('use') indicates the key'sintended purpose - signing or encryption.
An RSA key pair can also be generated with the standard Java cryptographicfacilities and then converted to JWK format: Generate a public key ubuntu.
A generated RSA key pair in JWK format:
EC key pair
Elliptic Curve (EC) keys are based on curves with specific mathematicalproperties. The JOSE WG adopted three standardcurves for EC keys and ECoperations with the following designations: P-256, P-384 and P-521.
To generate an EC key pair specify its curve:
To generate an EC key pair with the standard Java facilities and convert it toJWK format:
A generated EC P-256 key pair in JWK format:
Octet key pair
Octet key pairs are used to represent Edwards curve keys. They bear the JWKtype designation 'OKP' and are used for JSON Web Signatures (JWS) with Ed25519/ Ed448 and JSON Web Encryption (JWE) with ECDH with X25519 / X448.
Starting with v6.0 the Nimbus JOSE+JWT library can generate OKP JWKs with anEd25519 or X25519 curve with help of the optionalTink dependency. Edwards curve cryptographyis not supported by the standard Java JCA yet. For v6.0 of Nimbus JOSE+JWT theMaven dependency for Tink would be
To generate an OKP JWK just specify the name of the Edwards curve and any keymetadata required by your application:
Example Ed25519 key in JWK format:
Octet sequence key
The octet sequence JWK format is intended for representing secret keys, such askeys for use in HMAC and AES. A secret key is essentially a random array ofbytes that cannot be practically guessed.
HMAC key
HMAC computation requires a secret key which length must match the size of theoutput hash. You can also use longer keys, but they will be truncated.
To a generate a secret 256-bit JWK for HS216:
You can also use Java's SecureRandomor the dedicated KeyGeneratorto generate the key bytes and then use the bytes to create a JWK:
Example secret key in JWK format:
Shared Key AuthenticationAES key
Symmetric JWE requires an AES key. For example, directencryption with A128GCM requires a 128 bit AES key.
Random Shared Key Generator Hs256 Generator
As with HMAC above, you can use the provided the OctetSequenceKeyGeneratoror Java's standardKeyGenerator.
To generate a 128-bit AES JWK directly:
To generate the AES key using Java's standard facility, then convert to JWKformat:
Example 128 bit AES key as JWK:
Comments are closed.
|
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |