{"Illegal base64url string! (Parameter 'input')"}

[Jesterbester2]

So I'm trying to decrypt a jwe token, with an algorithm of RSA-OAEP, and encryption of A128CBC-HS256

I'm RSA to make a JWK object.
then I trying the code below:
rsa.FromXmlString( // PRIVATE XML STRING KEY );
var jwk= new Jwk(rsa);
JwtSettings settings = new JwtSettings();
settings.Jws(JwsAlgorithm.HS256);
settings.Jwa(JweAlgorithm.RSA_OAEP);
settings.Jwe(JweEncryption.A128CBC_HS256);
var jwe = Jose.JWE.Decrypt(token, jwk, JweAlgorithm.RSA_OAEP, JweEncryption.A128CBC_HS256, settings);

And everytime I try get an exception: {"Illegal base64url string! (Parameter 'input')"}

Below is an example of my token string, is there something I should be doing differently?

eyJhbGciOiJSU0EtT0FFUCIsImVuYyI6IkExMjhDQkMtSFMyNTYiLCJraWQiOiJwMTgifQ.JpnQn7b-XJ2E6aBbBI_uF4JBQR7CSZjE8a-xQBwhouM-jUCDP4IjDAM_TtOFqx1NF4etUTJ2aiZC-lB5XqI6Kbe2Alo8NXB16V5OmYj0kJrCL9x6yRFYI9LNsVxhPbV5a-AMdXPaeGaM0-_SRuvT8rtTR8AAsZP9f033jjR4g.ECocleCj4xSGc55bJ54fnw.1X9vLA7NQfOrOh6JZHAPjSSClsZx5kr22-bkcBp5WMzR_9oJesOoIQz7qDI5_75KVkpypbOrWcvFwUy9nQ23aSnPvhOcDNZEPyohOMf0A-28EQ87vNdXY4u5qbeLgMh5FHFkqFdKOoIFTkhnVaDg177thw5ZQ9iTJ0-Ar0j26ZCrerfgcA0OlSlBgWtEPD6QURCBgPMKWE4hAMGR2kyULg3k9FUueugp8BzJUnO2wDiTOpbXThRCFb5aOpjoXw4xf9OYlbuedHkZwYVdbdBC3w.4ZaZxKr-X4TA5ZKsmq2be7m7qCA6482VncSOL7LoVKw

[dvsekhvalnov]

Hi @Jesterbester2 ,

it doesn't look like your token is JWE? Jose.JWE.Decrypt() handles RFC 7516 json encoded tokens.

Can you try with Jose.JWT.Decode(token, jwk) instead?

[Jesterbester2]

I have tried both of them and neither work, also from my understanding jwt & Jwe. Jwts are seperated by two periods and JWEs are seperated by 4 periods the token above has 4, and I know for a fact the it was encrypted when it was originally made using JWtauthprovider.
So any help would be great i know in the code it is failing here
https://github.com/dvsekhvalnov/jose-jwt/blob/master/jose-jwt/util/Base64Url.cs
What does this mean?

[Jesterbester2]

@dvsekhvalnov dvsekhvalnov

By the way in case I didn't make it clear I'm trying to get the payload from the token?

[dvsekhvalnov]

Hi @Jesterbester2 , can you attach your key if possible, so i can run decoding myself?

Hard to guess without trying.

[dvsekhvalnov]

Hey, so i dig around, it seems 2nd part of token is incorrectly base64url encoded, it has wrong padding

JpnQn7b-XJ2E6aBbBI_uF4JBQR7CSZjE8a-xQBwhouM-jUCDP4IjDAM_TtOFqx1NF4etUTJ2aiZC-lB5XqI6Kbe2Alo8NXB16V5OmYj0kJrCL9x6yRFYI9LNsVxhPbV5a-AMdXPaeGaM0-_SRuvT8rtTR8AAsZP9f033jjR4g

you can check it yourself too at https://toolsaday.com/encode-decode/base64Url-decode for instance.

@Jesterbester2 where did you get this token from? What library generated it?