RSA Decrypt returns different byte[] results for same we

Question

As illustrated in http://msdn.microsoft.com/en-us/library/vstudio/system.security.cryptography.rsacryptoserviceprovider.encrypt(v=vs.90).aspx I am trying to use an RSA key that is stored in a User Container to encrypt and decrypt a RijndaelManaged Key and IV that is stored in an app.config file (in an NT service).

To create the encrypted keys I did the following and then added the strings to the config file

CspParameters cp = new CspParameters();
cp.KeyContainerName = "ContainerName";

// Get the existing or create a new RSA Key

RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(cp);

//Create a new instance of the RijndaelManaged class.

RijndaelManaged RM = new RijndaelManaged();

//Encrypt the symmetric key and IV.

byte[]  EncryptedSymmetricKey = rsa.Encrypt(RM.Key, false);

byte[]  EncryptedSymmetricIV = rsa.Encrypt(RM.IV, false);

string configKey = Convert.ToBase64String(EncryptedSymmetricKey));

string configIV = Convert.ToBase64String(EncryptedSymmetricIV));

When I go to use the Key and IV from the config file, I perform the following:

//Get the existing RSA Key from the USER Container identified by Provider in the appsettings

CspParameters cp = new CspParameters();

cp.KeyContainerName = "ContainerName";

using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider(cp))
{

    //Decrypt the RijndaelManaged KEY and IV from the config file using the RSA Key

    byte[] Encrypted_RM_Key = Convert.FromBase64String(AppSettings["configKey"]);
    byte[] Encrypted_RM_IV = Convert.FromBase64String(AppSettings["configIV"]);

    byte[] Decrypted_RM_Key = rsa.Decrypt(Encrypted_RM_Key, false);
    byte[] Decrypted_RM_IV = rsa.Decrypt(Encrypted_RM_IV, false);


    //Encrypt the file using RijndaelManaged
    RijndaelManaged RM = new RijndaelManaged();
    RM.Key = Decrypted_RM_Key;
    RM.IV = Decrypted_RM_IV;
    ....

}

While the service is running RM.Key and RM.IV stay the same. If the service is restarted, the resulting byte arrays in RM.IV and RM.Key are different which causes any decryption attempt on data that was encrypted before the service was restarted to fail with a Padding Invalid error.

Question: If I am using the same RSA key on the same encrypted data from the config file, why are the resulting Key and IV values different when the service is restarted?

Note: This also happens if I decrypt the values in my OnStart() service method and then try to decrpyt the same values in a dll that has been added to the project.

score 0 · Answer 1 · answered Jan 26 '13 at 00:48

0

Wild guess: is your service running as the user for which you stored the keys in the container? You can add some traces along the way (or debug) and see whether you get the same RSA key every time.

answered Jan 26 '13 at 00:48

On Freund

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Thank you for your response. Yes I did check that the service is running under the same user that created the Key Container. I did check to see if the RSA Modulus and Exponent are being set correctly, and they appear to be correct. – tspade Jan 28 '13 at 12:02
What about the encrypted key and IV? Are you always getting the same value from the configuration file? – On Freund Jan 28 '13 at 12:33

RSA Decrypt returns different byte[] results for same we

1 Answers1