I have created a new realm in Keycloak and in the admin tab Keys -> Active I can see three entries: RSA, HMAC, AES.
Whenever a JWT token is generated the signature algorithm used is RSA. How can I use HMAC instead?
I had the same question and found the following answers:
The latest documentation says that only rsa is supported for access tokens.
(http://www.keycloak.org/docs/3.3/server_admin/topics/realms/keys.html)
There is the plan to sign refresh tokens with hmac. Look at this user mailing list entry for more details:
"It is not great to sign accessTokens and idTokens by HMAC anyway since the
applications will need to have access to realm signing key. As it is
symmetric stuff. This can be security hole as then the application can
generate and sign tokens by itself. Hence we rather rely on the
asymetric cryptography - Keycloak signs tokens with private key and
application has just public key to verify signatures."
http://lists.jboss.org/pipermail/keycloak-user/2017-May/010809.html
Here is the JIRA for it:
https://issues.jboss.org/browse/KEYCLOAK-4623 and internally
https://issues.jboss.org/browse/KEYCLOAK-4622
In Keycloak 20.0.3 you need to go to "Tokens" tab and choose HS256 algorithm:
Recently, I'm trying to implement an OAuth2.0 server using JSON Web Token (JWT) as access token. I'm very confused about the self-contained feature of JWT. I notice that JWT can be verified anywhere, not mandatorily in authorization server because it is self-contained. How does this feature work? What claims should be included in JWT in order to realize self-contained feature?
Another question is that, if JWT is stateless, it means the server should not store the JWT. Then how is the JWT verified? Can't it be easily forged?
I'm the rookie in this field, I wish someone could help me out:)
JWT contains claims that can be signed, encrypted or both.
These operations are performed using cryptographic keys. Keys can be symmetric (e.g. octet keys) are Asymmetric (e.g. private/public key pairs such as RSA or EC keys).
When you want to verify a JWT (i.e. a JWS), you have to perform the following steps:
Check the header (algorithm is supported, critical claims are in the payload and their value are understood).
Check the claims (especially exp, iat, nbf, aud).
Check the signature.
To check the signature, you need the key and, depending on the algorithm, this key can be
The symmetric key
The public key if asymmetric
When you want to allow third party applications to verify your JWT, you will use asymmetric keys and share the public key with the third parties.
As public keys cannot be used to sign, third parties cannot forge a valid token with custom claims.
The way you share the keys is up to you. The common way is to provide an URL where applications will retrieve them (e.g. Google keys at https://www.googleapis.com/oauth2/v3/certs).
I'm implementing a sign in system with the help of the JWT (JSON Web Token) scheme. Basically, after a user sign in / login, the server signs a JWT and passes it to the client.
The client then returns the token with each request and the server verifies the token before sending back a response.
This is pretty much how you would expect it, but I'm having some problems with the logic of the process. From all the mathematical articles I've read, it seems that RSA signing uses asymmetric keys for signing. As the public key, as its name suggests, is exposed to the client and the private key is kept on the server, it makes sense to sign the JWT with the public key which is sent to the client and verify it on the server side using the private key.
However, on every example and library I see it seems to be the other way around. Any idea as to why it is so? If a JWT is signed with the private key and verified with the public one than whats the point?
First off, apologies, this answer got rather long.
If you use RSA to sign your tokens, and a connecting client is a web browser, the client will never see the RSA keys (public or private). This is because the client presumably doesn't need to verify that the JWT is valid, only the server needs to do that. The client just holds onto the JWT and shows it to the server when asked. Then the server checks to make sure its valid when it see's the token.
So why might you need a public / private key combo for JWT's? Well first off, you don't need to use a public / private key algorithm.
You can sign JWT's with a number of different algorithms, RSA being one of them. Other popular choices for signing your JWT's are ECDSA or HMAC algorithms (the JWT standard supports others as well). HMAC, specifically, is not a public / private key scheme. There's just one key, the key, which is used to both sign and validate the tokens. You can think of this as using the private key for both signing and validating the JWT's. I'm not an expert on this by any means, but here's the conclusions I came to from doing my own research recently:
Using HMAC is nice because it's the fastest option. However, in order to validate the JWT's, you need to give someone the one key that does everything, Sharing this key with someone else means that that person could now also sign tokens and pretend like they're you. If you're building multiple server applications that all need to be able to validate your JWT's, you might not want every application to have the ability to sign tokens as well (different programmers might be maintaining the different applications, sharing the signing ability with more people is a security risk, etc). In this case, it's better to have one, tightly controlled private key (and one app that does the signing) and then share the public key around with other people to give them the ability to validate the tokens. Here, the private key is used for signing the tokens, and the public key is used for validating them. In this case you'd want to choose RSA or ECDSA.
As an example, you might have an ecosystem of apps that all connect to
the same database. To log users in, each app sends folks to one,
dedicated, 'logging in' app. This app has the private key. The other
apps can verify that the person is logged in using the public key (but
they can't log people in).
The research I've done points to RSA being the better option for most JWT apps in this scenario. This is because your app will be, theoretically, validating tokens frequently. RSA is much faster then ECDSA at verification. ECDSA is primarily nice because the keys are smaller in size. This makes it better for HTTPS certificates because you need to send the public key to the client's browser. In the JWT scenario though, the keys are staying on a server so the storage size is n/a and the verification speed is more important.
Conclusion: if you're building a small app without multiple smaller 'micro-service apps' / you're the only developer, probably choose HMAC to encrypt your keys. Otherwise, probably choose RSA. Again though, I'm not an expert, just someone who recently googled this topic, so take this with a grain of salt.
There is a difference between signing/verifying and encrypting/decrypting data but the semantics can be similar.
You sign data with a private key that only controlled sources have so anyone who receives the information can use your public key to validate this information was indeed sent by you and is the same information you intended to send out.
You encrypt data with a public key and decrypt with a private key. This sounds opposite but really follows the same logical concept as signing. If you want to send data between person A and person B, both people have a public/private key pair and they share their public keys with each other when they meet (handshake). A constructs a message for B and encrypts it using B's public key and sends it to B. Now, no one without B's private key can decrypt that message including A - even though they originally sent it.
In terms of JWT, a JWT payload by itself is just Base64 encoded JSON with some standardized fields. The signature allows someone with the public key to validate the information hasn't been altered by someone in the middle. Similar to a checksum but with some extra security based warm fuzzy feelings. The contents of the signed JWT are easily visible (base64 is encoding like unicode or utf-8, not encryption) to the end user and anyone in the middle which is why it is generally frowned upon to send sensitive data in a JWT like passwords or PII.
As others have mentioned, most JWTs contain information not intended for clients but to help facilitate the stateless part of RESTful services. Commonly, a JWT will contain an accountid, userid and often permissions as "claims". An API endpoint can verify the signature and reasonably trust the claims to not be altered by the client. Having the client send the JWT for each request saves the endpoint having to do a lot of database back and forth just to get where they are by simply verifying a signature with a public key.
Additionally, signed JWTs can be encrypted. According to the JWE spec, the payload is encrypted after signing and then decrypted before verifying. The trade off here is that all endpoints must also have the private key to decrypt the JWT but end users won't be able to see the contents of the JWT. I say trade off because in general private keys are meant to be kept secure and a widely distributed private key is just less secure. Security, risk assessment and cost/benefit of encryption is a whole other beast :)
Your suggestion:
it make sense to sign the JWT with the public key which is sent to the
client and verify it on the server side using the private key.
is not correct. Signing is done with the private key of the sender, encryption is done with the public key of the receiver. That is how PKI works in general.
I am implementing a REST service which has RESTful authentication using jwt based on suggestions from this and this answers.
In constructing the JWT I have decided to sign it using an rsa public private pair rather than hmac for the obvious benefit of being able to keep my signing key fully private because I don't trust the clients that I will need to share the validation key with.
My question is, since normal https server certificates already use rsa keys, would it be acceptable to use that same key pair to sign a JWT token? One advantage I can see is that I will not have to maintain two certificates and mechanisms for sharing the public key with the client are already well established.
PS In case I sign the JWT with a new specific key pair, what is the best way of sending the public key to the client for use in verifying the token?
I created a token with the private key by JWT, but when I try to decode it on http://kjur.github.io/jsjws/tool_jwt.html, I found that the token can be decoded without any key given. So is it correct that the JWT token is just a signing? How to keep the token from decoded without the key?
There are two ways in which a public/private keys can be used by a JWT: signing and encryption.
If you use a private key for signing, it allows for the recipient to identify the sender of the JWT and the integrity of the message but not to hide its contents from others (confidentiality). Note that it would be the sender's private key that is used to sign the JWT and produce a JSON Web Signature (JWS) object. Apparently that applies to the JWT that you're looking at.
When using a public key for encryption it can be used to hide content from anyone but the intended recipient. The result is a JSON Web Encryption object. Note that it would be the public key of the recipient that is used to encrypt the JWT. Apparently that is what you're looking for.
See: http://jose.readthedocs.org/en/latest/