Question

Ok, I have a string of text, encoded in Base64.

I want to decode this from Base64 to a byte array, then decrypt this with my private key. My private key is a *.pem file. I am lost!

I think I need to declare a byte array, grab the text between the —BEGIN— and —END— part of my *.pem, and convert this from a base 64 string as the result of my byte array.

I then need to declare an X509Certificate2, and use the constructor that takes a byte array and a string of text, the byte array being my private key, the string of text being my passphrase like below:

byte[] myprivateKey = Convert.FromBase64String("BASE 64 ENCODED PRIVATE KEY GOES HERE");
X509Certificate2 myPem = new X509Certificate2(myprivateKey, "MY PASSPHRASE");

However, I am getting the following error at this point:

Cannot find the requested object.

Am I heading in the right direction at least or am I way off? What do I need to do here?

Answer 1

X509Certificate2 won’t read a private key from a PEM base64-encoded file. You’ll need to read the private key apart from the certificate and then assign it the the PrivateKey property.

See how to get private key from PEM file? for more details.