JWK alg field not matched with JWEDecryptionKeySelector when JWE header uses RSA-OAEP-256

[Former user]

Note the key information below is just demo keys and so are not sensitive. I used the command line JWK utility to generate my RSA keys to use when encrypting a JWEObject that has an embedded JWS Object.

The key:

  {
      "kty": "RSA",
      "e": "AQAB",
      "use": "enc",
      "kid": "4ed15d81-4fee-4cfa-89d0-ae58fdc26698",
      "alg": "RS256",
      "n": "twYvIZC29Bq9yoffwkaF4736HQaREsjqlOc0rjTSpyuurAFWJP_bwaZAYHVUf5tAORZrR0QqxdQ0R8lHOSkjK6ulqQf9PHFBRRkrFZkbCpxlSQiJq7l8Vk04_Cz-KLykTqQVoTcoTLH5iD5l-6LjZZcRGAAZkcdW7jBiJH58CLYka1bE61yb-TW4J0sDyDgjOfW18nazapz2WyVd8Qw4JTDTa-Fqdwov6VYhkEu8JlnHAdpDzcTdbPLulsBukinzZDoTef--GhJaZgQ0WxhX7EC9fDADO1vlhcVNwrI2rEV6ga1PdUTSpq3aHYPkhzFYfkdPb0QdPD7e7fLCN7STlw"
    }

Note the "alg" parameter is RS256. The utility will not let me specify the alg as RSA_OAEP_256.

I followed the examples on your site to create a signed then encrypted JWE. Its header:

{
    "kid": "4ed15d81-4fee-4cfa-89d0-ae58fdc26698",
    "cty": "JWT",
    "enc": "A256GCM",
    "alg": "RSA-OAEP-256"
}

When receiving the token, I create the JWEDecryptionKeySelector and try to find the correct key. Note the kid coming in the header matches the kid in my key set above.

selector = new JWEDecryptionKeySelector<C>(JWEAlgorithm.RSA_OAEP_256, EncryptionMethod.A256GCM, config.getInternalKeySource());

keyCandidates = selector.selectJWEKeys(encryptedJWT.getHeader(), context);

This returns no keys. The selector above is looking for a key with an "alg" of RSA-OAEP-256 instead but my key key in my key set has alg=RS256.

I can manually edit my JWK JSON to change the alg parameter to RSA-OAEP-256 and then it matches.

Is this the correct approach? I question it because the utility won't let me build this type of JWK.

Or is this a bug in the JWEDecryptionKeySelector where it doesn't translate from the JWEAlgorithm to a corresponding key algorithm?

Thanks! Great library!

• Mac

[Vladimir Dzhuvinov]

Hi,

You can use the -a command line switch to set the intended algorithm for the RSA key pair to be generated:

java -jar json-web-key-generator-0.4-SNAPSHOT-jar-with-dependencies.jar -t RSA -s 2048 -i 1 -u enc -a RSA-OAEP-256

This will output an RSA key formatted like

{
  "p": "8tB-vA1j4PVLRdJ7x2JRqbVb15B6sTHP71ij841bqu3fWSBHLTgAYfvpwLNuPSQlVA09j2PuEMtvPAS--0sPn5KGfFXNtOtKjpmQfu1F_-ePB3g5tprm6Fe_wBUwG7y8wf-PjI20HwEkHC1MWke2u42u3Dfr8REQb0RhpJKlhwE",
  "kty": "RSA",
  "q": "w5ipw9dWisWJWRxuqgPhZpMwn3a5LQFnTh60udWMUvta-yXjl8QQGqDY2dVg6G2Eg_sg_I3ZFOHT2lqJoHkQ9VDMoIEOgxaBWRyUPLNe6NIZouWt71AeviBOF4qOweddv7CwJ3x3sYHEqc7l4-Ib0P7K_eyTZRohXRIPHEjWnHk",
  "d": "iWAweUu3-E6Lgl9Cfdtc8iSDXDtQGJJhCk3TVphwvaOK1UTbUY4mabviTYC5NEw_AMULkh0NG8XJ8LYFOEXbKv4-4P5S8rzvZh3Krn_zLAOp2Z0C8Gf_0YsekCABahoNivpXtt2uVOe7u3q1btvIWLaI1ZHtz_5FjxaVnsnqIzoZeB0QQRqLl7FLQ3y3EJXe5uyNjiYK6nqmevWMIIsV2GM_gv3_lxmJqfHxvkX5rrT6BiQJa9YxLB37prVeHltqceeSw9JgjNFtjeL0C5xYIml20snfI7e080FjbVl9Ix_6sAF2M9ORiILLv2V-20Vb63v5uW5rTH5tCMJC3VrIAQ",
  "e": "AQAB",
  "use": "enc",
  "kid": "1",
  "qi": "R3jjHGCdIMjADph74r5JJC1EwoQ2CLewoGWLrxcmRcDpMr4A_j18M-8EdDMYV9L5Dk9gy3OmMclsyttUQBXpzJ0NTIcy0iMC-uOhv8MZp6yteLqVxoKtb88UaJaorHV55Atax3ZkR_0qDyzalfjOlazqFSK4NA4JwENd8LwEoJE",
  "dp": "0pxP4TNIF98L3FM2s_mu1aIOOIsEMOAA-R0MkHtjMH7FRNw_gJRbmKHV3iSEkRniGualJ9PIsd6S7B89vGAd_A4vAne2Rp_z-n5um_mYxuAF6re4b5AqiwtZsfVu1hA-NZNC4uoieuYVeS89U-1yLXo2WqNSzrU7aReKDiJ42wE",
  "alg": "RSA-OAEP-256",
  "dq": "XPoH0Ole4Q5vcKWcUUMQ9UKIfXThJ2ygX7km7aN-Vb_YCsSDAJSZlx7YlgvhSfstX9OTZZpEE7IZk5UwENEb55DmBHH0pQmgqOx15rjZJ9EfkJifar_qLTSMCpK5s6C4prNluQ9okj9-bb3E9-N2l41WjwfTNN8L9wLrneVd5vk",
  "n": "uYWdWeKU5dfQBYsC4YDZ1NMvQP0bC5pIGCzupvAMsUpQbg9gAWaAjlDZDMw6SSdNQrc1mMnuL0ql1W3QOrf22MPo2TJcq3F5uFvK6XZhArtPmqsDpF_ySumo_Kc7Wg-Ei3RZHXAL1IBGaL8ivtTUMS4WRb37objd7JPV-XeDs4nn7MWaJiUVbG9tL9_bynxi2YTNeKC0xtWnbqnfohE4NFeELe4jsi5A4kObX9MeZfj0XyWJCYJM9nuL7aaVzb8sjo1m3kMXo7KLP-BS5ZERVnI0ouXGaT2qc5fRkmzdjJ_PUBqZQPlVMDDOu4CmPz2rDJFX-q_cmJnDuWeZUVdreQ"
}

Editing the "alg" in the JWK is also fine.

The JWK generator is actually maintained in a different project, by Justin Richer, at https://github.com/mitreid-connect/json-web-key-generator.

The JWEDecryptionKeySelector is quite strict, and if a JWK is marked for some other algorithm, it will be skipped.

Hope this helped. Thanks for the feedback!

Vladimir