Exception: Cannot access a disposed object. Object name: 'RSACng'.Trying to decrypt JWE ciphertext using C# System.Security.Cryptography - .pem key

Question

I'm trying to get the Ciphertext out of a JWE response using C# and a PKCS 8 private key and cannot find a good example that works. I created the public and private keys using: openssl genrsa -out private.pem 2048 && openssl rsa -in private.pem -outform PEM -pubout -out public.pem && type public.pem

When I run this code it seems like it read the PEM key information fine, but there is zero bytes of output and I get "Cannot access a disposed object. Object name: 'RSACng'." when trying to use the RSA object.

Here is the code and the JWE + Private key data:

My goal is to get the Ciphertext out of the JWE string. Here is the code and the JWE + Private key data:

using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System;
 using System.IdentityModel.Tokens.Jwt;
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
 using System.Security.Cryptography.Pkcs;
 using Microsoft.IdentityModel.Tokens;


 namespace Transaction
 {
     public static class CallDecryptJwe
     {
         public static void DecryptJwe(string jweString, string decryptionKeyInput)
         {
             string jweToken = jweString;
             string privateKeyPem = decryptionKeyInput;

             JwtSecurityTokenHandler handler = new JwtSecurityTokenHandler();

             //JWE Payload (string jswString)
             /*
              * 

    eyJraWQiOiIzM2MzZmNmYTI1YzkxMWUzMTBiNDBjZGYwZWMxMWFhOWQxY2Y2YzUzIiwiY3R5IjoianNvbiIsInR5cCI6IkpXVCIsImVuYyI6IkEyNTZHQ00iLCJhbGciOiJSU0EtT0FFUC0yNTYifQ.v0f_8g-OW86e81KBGACnR6jiqr8VC9HnFo8X3tyRYeulTFfh1rxHwtpq7RTTtsNs_bjhoexOG4i_MFuk1eCR4ex0VpCGmUssbpnEkttQ83EZEfPYalQf1oMhqHyHDVNjQ3vdQma8B7ucG6ru71HfnPF5iWAefMRNm6GQXFwqhRbD9XOXitw7KS8KWjucsHyGmhb2Ye3q0nHc6zEgAN2AfiX8xsfsbx73ajU0bl0cuaRbZVsFfadnjggFngRfp2eTu0MPVf8YriiLXqpe4g6uQo0ERECZpzO6QePZXlxA2GB04yURZLMqZiRpgfMvifYc9W07Y-vjJ6s8hq1T5MKA2A.d6wRkpDHrANCUIVS.uM6N3gWAfefOSQXQKHOqIntCrV1HmsJ8QSy2fGm2Z542PqXiJYyWYV6MiGWdqOgmkTYBMf5VIId319b75q9hOXn1f-idSyiDYlvW9uIF3eb-Nd9ZQ6OrEG6vXG833mE0uJ4hzxnzjKPspUYD95gLG21cuBLl4yeM52Gi3bqB9Sc8RcSQpl8gLcNce-h9VZmE_J4pCnS3eIDNwZT_UBP7tjuQ6ILpourxpn_f3YmUzKvOfROuLFfCPi4_TqMXHemEJvnzUUahtLtx8G8TlmUDAU9vQk7KjDiLtgbJAf7lLn9hoU01YnfAMEgLkkdtpwRAk6h12tbA7pD3eapjdwDuQAjGOj2_a1eVfAp5wjimCD_VYQJXTj8VHtiZ5-qD_F2Dd5PmnytK5o1zx3ceTQyEPGehYFeqzijqE7HjKleT2fmK-fcBWRswtL9Y5w8IJSDI4TLE0TtuCGwmaiSWwex2s3NJmLUJ7M2NuIu6m1TNfeyN7-l63HCpG4PXCO2CizzMQp1Yyb09EVq1cQ_VPweEXq1Xl9su2dOfbcX-_l_qib4KevCXIsL_aSJsO-hn1iWDTX8aHzbvx0wuPrDhrqrUYrYdVmdklBQEgLbhsVjvo8HwF___3sg_d9Vivs2XsxNG77JQdOYRvs7aHo5Gkl338rdhyQMkptz77KH6K71fMi8zGLRqgvTsiE-oUsveGcN7AxzxnNYv6FjQeWCxqo9eLjlC6A5ClNpEFOe32aITVrk44nDWx2M7s0KO2ZdmWQVVK4HeDqoFA5MOCRGJVOx0PrCLGK3EdmLKEauWs_kC9V9pyAGn27ScrbadKzv4HsPUOfG8kvwcpizXdC_EgeVlsFxOGGpuOl9nTmCh7DrNxNLkdwl2V1MCZfkLY6dKP33Hb5w4xrUzV5UrgLgkt6rXDmfiHDE28HYz-KHOmb16UUK67CEUnmYAt38XSyjwLA7Jt-aHAz1e6iSbPG2PexE.fPOiZh0ZOgXgPdtzUmV_vQ
             */

            try
            {
                // Convert PEM private key to RSA object
                RSA rsaPrivateKey = LoadPrivateKeyFromPem(privateKeyPem);

                // Create RSA security key for decryption
                var rsaSecurityKey = new RsaSecurityKey(rsaPrivateKey);
                var validationParameters = new TokenValidationParameters
                {
                    TokenDecryptionKey = rsaSecurityKey
                };

                // Decrypt the JWE token
                var claimsPrincipal = handler.ValidateToken(jweToken, validationParameters, out var securityToken);

                // You can now access the decrypted claims
                Console.WriteLine("Decrypted claims:");
                foreach (var claim in claimsPrincipal.Claims)
                {
                    Console.WriteLine($"{claim.Type}: {claim.Value}");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error: {ex.Message}");
            }
        }


        //private.pem file (string decryptionKeyInput)

        /*
                -----BEGIN PRIVATE KEY-----
        MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQDKiKyfq8/SUQk0
        o6Tc5rReV9HWA28YGP1TwWi7MolB6G7Bf4OoPEds1PFdUXAbbfLHwRF4v9ZBTY3d
        cORNIfT8ZyY9RSxwoO6TVEXAUYsOafEp2mzmv93gpvh4ct9LZKkhSbSibkU11oEE
        9vWcroHMVelUsJ59j9P7UtdJfjlOvm4x3sntjy0f3Lg8Lf6eltO1qxFVofxsOX2r
        +/e1a7fJb6aZspBvK5WmoeJuiGR+F6OxvNp6LlvgQGz8aNK2F1E2yW6YUIwMkLhw
        X1qXuvHEMtTctAISdQUHnSusJ/9vjEK7oZmGzt47GAFVcngbJchCRzmbu8Vh7Smv
        in+xahR1AgMBAAECggEADVXzAd97A2btE3979USmlziymyQmPkC0+30Wc48IDSQs
        GMcX6O2xKUgbLXEVj+TNMdxzVU9SYQHlh7FtguuruSvkj2+81ZyvINnRbvCflp8g
        r0gP2CDFkAuGfE3aCJmT7lpvT6uxmHIrlCNbuEmgR89XWgl4Ih3kkB2cCd2LEfVn
        iLqVY+zAkvCW9nQ8ap8xLSdJ1JIWxCLK3VWeO0OU1U/EabwtcDyGdJvtpWp8UQfK
        VJuRNJedsFaplxWkM3fAhsIpEdKwQ1yHqc0+Buc5BtFdMj2dbq/ydo2VZ1BNvcO0
        b23fnkw6l5Gh50xoT5vz6tuIkGcDxk+SB28wtdvAUQKBgQDl1HRiQQe6J9MrASjJ
        zsNQAV/JPb5LeXutTYOnJsbgr9Wxjyt+kfJ8a2MHUdFt/nmeEtJoeDevhR2tR2ly
        8TCVGSaYxTSWmbmmwCAa9vrlV4Ei7Qgyr+9BALagVcCx4GH8fmHQ598d0q91Ctqb
        zAior/6jTeFyiW+f9lUQxnG7EQKBgQDhmIpUTdLsvGB3xG8ItmY0zApw31fX6Tsy
        O2kFFq+hq3lvHa8eTDioNdbM6cbc5ic/bHdlhnXoWcAcfZ6GVqJ7eyo1h+Ztm31a
        quYMrKUPX6JnQVt5dw5SYEUnkxwe6UwMPdqO9k0H80ndMwITGB6AREoiW7NOqKeF
        AcOvT8tbJQKBgCi9RTgZcOY1ov/vf6xuIz7uT21brXyxdxPcNqcNf5lacdW8nCge
        dM5LNs2YWjhWMHatvXBZRv2s6frKOs3uJP946tePtWewrjD5w3ckKos2vKRVQevC
        NfXey4CWUsb1EElymaIvR+SAcSudFe0h+LL2J3wJFRp5dDj1sFR96LERAoGAKaiH
        csXkOz8V+UfW0R8NhJZhHzK+/+nbuozp+byUth/6DqDGo6ujkrxObAyHYmdFvBqF
        ecP4pe1c4mX4DgqVeoPl6Xis/nSGE2YXkSOYX1xjmvmgsK9hf6izXHl36eVe26vY
        XinxU5SDgUtYCLqdd0YlAm84jz/pn1ASGJ99h9kCgYBbMjqWBJlowrpIn4ETFpDY
        VOhgIgvg8blAi0d0xi+0D48k8iMg1cBU6/0RZsNuXR7Vf7Qls+Gqf2kRop6fR+1n
        Qiysm/nzzpLKNRsU+7tZvJ3Ybp9Nw/DC8Hl/zMnQva9JEfnu+tH6iqcNOXrJRP4N
        5dI4kF52AUbUSDd61VP7sQ==
        -----END PRIVATE KEY-----
        */

        static RSA LoadPrivateKeyFromPem(string privateKeyPem)
        {

            // Load RSA private key from PEM format
            using var key = RSA.Create();
            **key.ImportFromPem(privateKeyPem);** // this throws no exception but doens't seem to create an RSA object either.

            return key;

        }


    }

}

Answer 1

Your use of using var key = RSA.Ceate() is causing the return of your function to call RSA.Dispose() before it can be used correctly by the calling code.

You could start by changing your code to:

static RSA LoadPrivateKeyFromPem(string privateKeyPem)
{
    var key = RSA.Create();
    key.ImportFromPem(privateKeyPem);
    return key;
}