Microsoft® Visual Basic® .NET Programmer's Cookbook

Combine Asymmetric and Symmetric Encryption

Problem

You want to use symmetric encryption (perhaps because you need to encrypt a large amount of data, or performance is very important), but there is no shared secret that you can use.

Solution

Create a random symmetric key, and use this key to encrypt your data symmetrically. Then encrypt the random key asymmetrically.

Discussion

Asymmetric encryption is typically 1000 times slower than symmetric encryption, and the encrypted data it creates is several times larger. You can avoid these limitations by generating a random symmetric key, and using it to encrypt the bulk of your data. The trick is to encrypt the random key using asymmetric encryption with the recipient’s public key, and then add it to the ...