Simple example to generate A Shared Access Signature that can be used to share URL for file storage

gistfile1.cs

var fileName = "sascontainer/sasblob.txt";
var startTime = "2015-04-29T22%3A18%3A26Z";
var expiracyTime = "2015-04-30T02%3A23%3A26Z";
var permissions = "rw";
 
 
var message = string.Format("{0},{1},{2},{3}", fileName, startTime, expiracyTime, permissions);
var messageBytes = Encoding.UTF8.GetBytes(message);
 
// Chave: Só o servidor conhece
byte[] secretkey = new Byte[64];
using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
{
    rng.GetBytes(secretkey);
}
 
 
// Assinatura
string signature;
using (HMACSHA256 hmac = new HMACSHA256(secretkey))
{
    byte[] hashValue = hmac.ComputeHash(messageBytes);
    signature = Convert.ToBase64String(hashValue);
}
 
// Validação
bool err = false;
using (HMACSHA256 hmac = new HMACSHA256(secretkey))
{
    byte[] storedHash = Convert.FromBase64String(signature);
    byte[] computedHash = hmac.ComputeHash(messageBytes);
 
    for (int i = 0; i < storedHash.Length; i++)
    {
        if (computedHash[i] != storedHash[i])
        {
            err = true;
            break;
        }
    }
    if (err)
    {
        Console.WriteLine("Hash values differ! Signed file has been tampered with!");
    }
    else
    {
        Console.WriteLine("Hash values agree -- no tampering occurred.");
    }
}