C# 5.0 Programmer's Reference

Asymmetric Key Encryption ❘ 615
numbers are also enormous (64 bytes or longer) so finding numbers that work isn’t as simple as generating
random bytes.
You can create a new set of key parameters by making an instance of the RSACryptoServiceProvider
class. You can then publish the public parameters and save the private parameters so that you can later
decrypt messages.
Microsoft correctly points out that you should never store key values in plaintext on a computer, so
cyber-crooks can’t find them. You could write down the D, DP, DQ, InverseQ, P, and Q parameters
on a piece of paper, but that’s a lot of data.
To help solve this problem, Microsoft suggests that you store key information in a key container, an
object that stores key information encrypted, so it’s not easy to steal.
If this all seems complicated, you’re right, it is.
The following list summarizes the steps for creating RSA keys in a C# program.
1. Create a new RSACryptoServiceProvider object. (It is created with a usable set of key values.)
2. Use the object’s ExportParameters method to extract the key values.
3. Save the key values in a key container for later use.
4. Publish the public key values Exponent and Modulus.
The following list summarizes the steps for using RSA to encrypt data in a C# program.
1. Create a new RSAParameters structure.
2. Initialize the structure’s Exponent and Modulus parameters with the public values.
3. Create an RSACryptoServiceProvider object.
4. Call the object’s ImportParameters method to set its public key parameters.
5. Call the object’s Encrypt method, passing it the bytes to encrypt.
The following list summarizes the steps for using RSA to decrypt data in a C# program.
1. Create an RSACryptoServiceProvider object, initializing its parameters with the
values saved in the key container. (Alternatively, you can create the object and then use
ImportParameters to load the key parameters from an RSAParameters structure.)
2. Call the provider’s Decrypt method, passing it the encrypted bytes.
The following sections show code that performs these steps.
Creating, Saving, and Retrieving Keys
The following code shows how a program might create new RSA key data and save it into a
key container.
// Create the parameters object and set the container name.
CspParameters parameters = new CspParameters();
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