Decode the JWK encrypted key before passing it to the jose.ParseEncryted function

[njunot]

When using JWK, Step CA sends out the Base64-encoded encrypted key. Currently that key is directly fed to jose.ParseEncrypted which expects compact JWE format and not the raw Base64 string. This fix attempts to decode the Base64 encoded key before passing it to the ParseEncoded function. If that doesn't work, it is assumed the string was already decoded so the encrypted key is passed as is.

Pain or issue this feature alleviates:

This issue resolves the error "error":"error parsing provisioner encrypted key: square/go-jose: compact JWE format must have five parts" that is encountered with step-issuer. It allows a step-issuer instance to issue certificates using the JWK from the corresponding Step CA instance.

Supporting links/other PRs/issues:

smallstep/step-issuer#107

💔Thank you!

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[maraino]

Hi @njunot, the response is not base64 encoded, it's a JWE

$ curl https://localhost:8443/provisioners/P1zJB3C7CQiUmU7zxpF-knn3PwipbKAKgGILDgDtT84/encrypted-key
{"key":"eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJjdHkiOiJqd2sranNvbiIsImVuYyI6IkEyNTZHQ00iLCJwMmMiOjYwMDAwMCwicDJzIjoiUV9nZkJfckdBZFFTNHlaVzNKUlRLQSJ9.O1V9h-AlL7I-38-8_ceEUPWH8cPNh83MrujO6Os_KhSGlUREAWD-CQ.ttb1n-CNAssaugcR.5pBdDgfuIMM0Og1v_afwhKdlj5OOJdo_wmLK0yzvk9aT78ftS1dopcL74rrncGOuG9i5TVnC4aLLibcSbO3HvG-rPZsTzvmzz9zBPTkga0fOicPPChiEUo5F2jd7wHs42UuJmxKjZdXsbLd7WgBRl6Jo6ll835NSN8_kNiqRPi79BmbwIsPn4wJ_PLybB-eeNweDh08AAuVuofXvk7dQzvWy37fsDQNpFChnzrUQlhjn5InjWsd6MpeA1hoA27DSi85Yd6JzJm7w8MMAggoNh_WlmPLscTOAhcsFnx_73PtKVRfPKyK2fZlC0dcsMbNWAVW-YKVrEAH_QTAiFwY.29BybdokVLvPTS_-ZC7J2w"}

It has 5 parts that are base64url encoded as explained in RFC7516 section-3.1

You can decrypt it like this:

$ curl -s https://localhost:8443/provisioners/P1zJB3C7CQiUmU7zxpF-knn3PwipbKAKgGILDgDtT84/encrypted-key | jq -r .key | step crypto jwe decrypt --password-file <(echo asdf)
{"use":"sig","kty":"EC","kid":"P1zJB3C7CQiUmU7zxpF-knn3PwipbKAKgGILDgDtT84","crv":"P-256","alg":"ES256","x":"G-g5Qs9rTVLCPxgIj5ywwfkSyMYbdr2-fTNgcZChRA4","y":"4oBKBibmwFik83IHfM44uT64hmWTXC68n0xlJhhPvgg","d":"RT5hyC61UDp2tcqNuZ7KmFdPY1vSfJkRQ_q0pKvDrnA"}

[hslatman]

@njunot how was the JWK provisioner created / initialized? As @maraino mentioned, the encrypted key should be in JWE format, and thus base64 decoding first should not be needed. Also see the example in our docs: https://smallstep.com/docs/step-ca/provisioners/#example.

[njunot]

Apologies for not replying earlier. The fault comes from my side. I am quite unfamiliar with JSON Web Encryption.

For the background, I've been working on automating the configuration of a Step CA on Kubernetes using Ansible. To that end, the whole configuration had to directly present in the configuration file. I chose to use the JWK provision to circumvent ACME limitations such as HTTP communication. On Kubernetes, HTTP communication isn't possible without the installation of a CNI (for which I wanted to have an automated Certificate Authority).

First, I created the JWK using step crypto jwk create ansible/pub.json ansible/priv.json --password-file=ansible/step_ca_password. Next, I imported the pub.json and priv.json files in Ansible which stores these content in base64 encoding. Then, I added these content of the file in my ca.json file. For pub.json it was quite straight forward because it was just clear text. For priv.json, I did miss the It's a JWE compact string containing the JWK representation of the private key-part and assumed from the example that the encryptedKey was a base64 string, given that both base64 and JWE string start the same way.

In conclusion, I saved my encrypted Key as Base64 string instead of a JWE string. My StepIssuer instance expected a JWE string but received a Base64 string instead which made him complain that the encrypted key must have 5 parts and thus preventing it from completing its initialization. I implemented my fix which decoded the Base64 string and revealed the JSON encrypted key, hence priv.json, as it was returned by step crypto jwk create.

Given, that the error is entirely from my side, I'll retract this PR. But before doing that, it seems like the jose.ParseUncrypted function works either its input is a JWE or the clear text encrypted key. Nice on that part, but is this an expected behavior? If not, a warning that a JWE is expected will be welcome.

[maraino]

Given, that the error is entirely from my side, I'll retract this PR. But before doing that, it seems like the jose.ParseUncrypted function works either its input is a JWE or the clear text encrypted key. Nice on that part, but is this an expected behavior? If not, a warning that a JWE is expected will be welcome.

@njunot, what do you mean exactly? We don't have a jose.ParseUncrypted method.

I suppose you're talking about jose.ParseEncrypted. It accepts only a JWE, but in both JSON or compact format.

step crypto jwe encrypt will return the JSON format, but you can pipe it to step crypto jose format to switch to the compact format.

$ echo asdf | step crypto jwe encrypt --key my.key
{"protected":"eyJhbGciOiJFQ0RILUVTIiwiZW5jIjoiQTI1NkdDTSIsImVwayI6eyJrdHkiOiJFQyIsImNydiI6IlAtMjU2IiwieCI6IlZjdGwweDItVnVYUmpNOG4yMTJONzY2MXVYLVlFZzZuMHIzTkhIQmluVEkiLCJ5IjoiOEF1ZFhOZ3ZuTUROb2Fla2JBbk1hU2tzNFRnck1QUW53a2ExcjVCQ2stcyJ9LCJraWQiOiJSS1oyTVVrV3A5M25NVG12el9za2RrNU1nSmNkV0dLNGU0RFNncGZWYmRZIn0","iv":"RmnHzV61WCQCmU8b","ciphertext":"vw9cflU","tag":"UcDvxFmnNyDxESAhRkL-QA"}
$ echo asdf | step crypto jwe encrypt --key my.key | step crypto jose format
eyJhbGciOiJFQ0RILUVTIiwiZW5jIjoiQTI1NkdDTSIsImVwayI6eyJrdHkiOiJFQyIsImNydiI6IlAtMjU2IiwieCI6Im9GNVRuVzktcVFRVS1pRmdSc0pVS2VrZDdSaDktdmNXWjhVUXo0eEp0emsiLCJ5IjoiYmM2STAwTXlzcFk3WTNwbjdRT21vZTJXRkVEM1VnMURxVGNqV2lVbGhUUSJ9LCJraWQiOiJSS1oyTVVrV3A5M25NVG12el9za2RrNU1nSmNkV0dLNGU0RFNncGZWYmRZIn0..yyMDF5q4C3ZnCOo-.E30Vg34.djtpM4FfmDW7xEug5Rha7g

[njunot]

@maraino Your supposition is exactly what I meant. Since it is an expected behavior, there is nothing to add.

Thanks for your patience and keep up with the good work! These products are amazing!