C# 4 and .NET 4

558 ❘ ChaPTer 21 security
Comparing the symmetric keys created from Alice and Bob shows that the same key value gets created.
Using this symmetric key and the initialization vector, the message from Alice can be decrypted with the
AesCryptoServiceProvider class.
private static void BobReceivesData(byte[] encryptedData)
{
Console.WriteLine("Bob receives encrypted data");
byte[] rawData = null;
}
var aes = new AesCryptoServiceProvider();
int nBytes = aes.BlockSize 3;
byte[] iv = new byte[nBytes];
for (int i = 0; i < iv.Length; i++)
iv[i] = encryptedData[i];
using (var bobAlgorithm = new ECDiffieHellmanCng(bobKey))
using (CngKey alicePubKey = CngKey.Import(alicePubKeyBlob,
CngKeyBlobFormat.EccPublicBlob))
{
byte[] symmKey = bobAlgorithm.DeriveKeyMaterial(alicePubKey);
Console.WriteLine("Bob creates this symmetric key with " +
"Alices public key information: {0}",
Convert.ToBase64String(symmKey));
}
aes.Key = symmKey;
aes.IV = iv;
using (ICryptoTransform decryptor = aes.CreateDecryptor())
using (MemoryStream ms = new MemoryStream())
{
var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Write);
cs.Write(encryptedData, nBytes, encryptedData.Length - nBytes);
cs.Close();
rawData = ms.ToArray();
Console.WriteLine("Bob decrypts message to: {0}",
Encoding.UTF8.GetString(rawData));
}
aes.Clear();
When you run the application, you can see output similar to the following on the console. The message from
Alice is encrypted, and decrypted by Bob with the securely exchanged symmetric key.
Alice sends message: secret message
Alice creates this symmetric key with Bobs public key information:
5NWat8AemzFCYo1IIae9S3Vn4AXyai4aL8ATFo41vbw=
Alice: message is encrypted: 3C5U9CpYxnoFTk3Ew2V0T5Po0Jgryc5R7Te8ztau5N0=
Bob receives encrypted message
Bob creates this symmetric key with Alices public key information:
5NWat8AemzFCYo1IIae9S3Vn4AXyai4aL8ATFo41vbw=
Bob decrypts message to: secret message
aCCess ConTrol To resourCes
With the operating system, resources such as files and registry keys, as well as handles of a named pipe, are
secured by using an access control list. Figure 21-3 shows the structure of how this maps. The resource has a
security descriptor associated. The security descriptor contains information about the owner of the resource
www.it-ebooks.info