pEYjR8pR

1var fileName = "sascontainer/sasblob.txt";
2var startTime = "2015-04-29T22%3A18%3A26Z";
3var expiracyTime = "2015-04-30T02%3A23%3A26Z";
4var permissions = "rw";
5 
6 
7var message = string.Format("{0},{1},{2},{3}", fileName, startTime, expiracyTime, permissions);
8var messageBytes = Encoding.UTF8.GetBytes(message);
9 
10// Chave: Só o servidor conhece
11byte[] secretkey = new Byte[64];
12using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
13{
14    rng.GetBytes(secretkey);
15}
16 
17 
18// Assinatura
19string signature;
20using (HMACSHA256 hmac = new HMACSHA256(secretkey))
21{
22    byte[] hashValue = hmac.ComputeHash(messageBytes);
23    signature = Convert.ToBase64String(hashValue);
24}
25 
26// Validação
27bool err = false;
28using (HMACSHA256 hmac = new HMACSHA256(secretkey))
29{
30    byte[] storedHash = Convert.FromBase64String(signature);
31    byte[] computedHash = hmac.ComputeHash(messageBytes);
32 
33    for (int i = 0; i < storedHash.Length; i++)
34    {
35        if (computedHash[i] != storedHash[i])
36        {
37            err = true;
38            break;
39        }
40    }
41    if (err)
42    {
43        Console.WriteLine("Hash values differ! Signed file has been tampered with!");
44    }
45    else
46    {
47        Console.WriteLine("Hash values agree -- no tampering occurred.");
48    }
49}