Should jwt web token be encrypted?

Question

I was reading article on JWT web token as an access token that is being response to the user. Some of it mention that the web token should be able to be decoded by the user.

Does it means that it is not a good practice to decrypt the entire web token? For example, I suppose to return following JWT web token to user where this piece of information can be decoded.

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ

However, I feel that I do not want to let user able to decode his/her access token, so I use another encryption algorithm to encrypt everything into another form as follow and pass back to user.

So, I would decrypt this new text when I'll get this access token in the server and decode it.

Is it recommended to do it this way if I do not wish to expose some of the value available in claim (such as user id) to the user? If not, what are the alternatives?

Answer 1

JWT (RFC7519) is just a compact way to safely transmit claims from an issuer to the audience over HTTP.

JWT can be:

• signed (JWS - RFC7515)
• encrypted (JWE - RFC7516)
• signed then encrypted (this order is highly recommended). The whole JWS is the payload of the JWE
• encrypted then signed.

It makes sense to encrypt a JWS if you want to keep sensitive information hidden from the bearer (client) or third parties.

The real questions are: does the audience support JWE? If yes, which algorithms are supported?

Answer 2

JWT are "signed" and therefore its contents are protected from tampering: you cannot change its contents without invalidating them.

You can optionally "encrypt" the contents and therefore turn them visible only to issuer (the entity creating the token) and the consumer (the entity that is destined to use its contents after verification).

There's a standard for that: JWE