Encrypted JWTs?

I’m looking to create an encrypted JWT and I’m a little lost.

Option 1: Articles like this one suggest just encrypting the string representation of a JWT: https://www.owasp.org/index.php/JSON_Web_Token_(JWT)_Cheat_Sheet_for_Java#Token_information_disclosure

Option 2: However, this article suggests nesting a signed JWT inside an encrypted JWT: https://connect2id.com/products/nimbus-jose-jwt/examples/signed-and-encrypted-jwt

My preference would be to use option 2 as I assume this is the correct way of encrypting a JWT. I can’t seem to find the right overloads and/or properties in the JwtSecurityToken object though to make it work. On the JwtHeader I see a property called Cty which is great, because I need to use that to set the content type, and on the JwtSecurityToken I see a property called InnerToken which looks promising. I don’t, however, know how to set that property and/or create a JwtPayload that wraps an existing JWT.

Has anybody else done this before and able to provide a sample?

[jacobslusser]

@brentschmaltz, thanks for your response. I have some follow-up questions.

Funny you mention that… after posting I persisted for another couple hours and found the JwtSecurityTokenHandler.CreateJwtSecurityToken method – a parent to the one you mentioned. As far as I can tell, that is the only way to create a signed and encrypted token because all the other methods seem to want SigningCredentials or EncryptingCredentials, but not both. Perhaps you could show me otherwise?

So the code I currently have is like this:

var now = DateTime.UtcNow;
var key = Encoding.UTF8.GetBytes("C9CB44D98642A7062A0D39B94B6CDC1E54276F2E7CFFBF44288CEE73C08A8A65");
var securityKey = new SymmetricSecurityKey(key);

var claims = new[]
{
    new Claim(JwtRegisteredClaimNames.Sub, "1234567890"),
    new Claim("name", "John Doe"),
    new Claim("admin", "true", ClaimValueTypes.Boolean)
};

var jwt = new JwtSecurityTokenHandler().CreateJwtSecurityToken(
    issuer: "example.com",
    audience: "example.com",
    subject: new ClaimsIdentity(claims),
    expires: now.AddMinutes(30),
    issuedAt: now,
    signingCredentials: new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256),
    encryptingCredentials: new EncryptingCredentials(securityKey, JwtConstants.DirectKeyUseAlg, SecurityAlgorithms.Aes256CbcHmacSha512));

var token = new JwtSecurityTokenHandler().WriteToken(jwt);

Console.WriteLine("Encrypted JWT: " + new JwtSecurityTokenHandler().WriteToken(jwt));

Console.WriteLine();
Console.WriteLine("Push ENTER to exit.");
Console.ReadLine();

The result is:

Encrypted JWT: eyJhbGciOiJkaXIiLCJlbmMiOiJBMjU2Q0JDLUhTNTEyIiwidHlwIjoiSldUIn0..kv71w0GLaULzcsdYyuOFSw.96gllkIz90WGtYt03kwqaEa4pUsODH0dpv0hh8HmjoukVvCPgT-apO_zUQwXO1dJkQbhtXqOCBjoEtqG-dpziUgfaZEz_4_XXpyNj8_v24mx8atPfcRDbTgHpgKSY2iZ-5thiXrSojmpVW6vIWksp7uKRN9BUA-ZC-QtLiUpyMVPP40Ft341bKfLF2jaAiYcwsRsUszb7KFE3Xy7fjwarlXemqGQbH3JamZVQo4vxxobg9z6BB0853AoBXewsV4V5GPFBXCv7WURblw3kp3Epe-lnHjdUbIY3kOhWeaPKDzoCAelUMqAoszvjQ1_1mAxDmV6rufaAB6kBLveDd2V4xM6leoFP3bZaP7sWiCJjYc.JuXpkjiUIj6BQqLgEW4W2NAH9Hr5SoHXYTd26TkdshI

As you can see, the second part of the JWE – which as I understand is the encrypted key – is empty. Why is that?

Finally, I would love some clarification around the choice of encryption algorithms. I’m trying to create a JWE using AES-GCM and AAD, as mentioned in my first link, however, I’m not sure if .NET supports this algorithm. Do you know?

[brentschmaltz]

@jacobslusser I will close this now. Please feel free to re-open if you need additional info.