asp.net "Remember Me" cookie - asp.net

Question

I have implemented remember me option in my asp.net webform by using this,
protected void LBtnSubmit_Click(object sender, EventArgs e)
{
if (this.ChkRememberme != null && this.ChkRememberme.Checked == true)
{
HttpCookie cookie = new HttpCookie(TxtUserName.Text, TxtPassword.Text);
cookie.Expires.AddYears(1);
Response.Cookies.Add(cookie);
}
}
Am i doing it the right way? Any suggestion.. I am using windows authentication and i am not using asp.net membership..

Answer 1

Rather than directly storing the username and password in the cookie, store the username and a hash of the password and a salt in the cookie, then when you authenticate the cookie, retrieve the password for the given username, re-create the hash with the password and the same salt and compare them.
Creating the hash is as simple as storing the password and salt values together in a string, converting the string to a byte array, computing the hash of the byte array (using MD5 or whatever you prefer) and converting the resulting hash to a string (probably via base64 encoding).
Here's some example code:
// Create a hash of the given password and salt.
public string CreateHash(string password, string salt)
{
// Get a byte array containing the combined password + salt.
string authDetails = password + salt;
byte[] authBytes = System.Text.Encoding.ASCII.GetBytes(authDetails);
// Use MD5 to compute the hash of the byte array, and return the hash as
// a Base64-encoded string.
var md5 = new System.Security.Cryptography.MD5CryptoServiceProvider();
byte[] hashedBytes = md5.ComputeHash(authBytes);
string hash = Convert.ToBase64String(hashedBytes);
return hash;
}
// Check to see if the given password and salt hash to the same value
// as the given hash.
public bool IsMatchingHash(string password, string salt, string hash)
{
// Recompute the hash from the given auth details, and compare it to
// the hash provided by the cookie.
return CreateHash(password, salt) == hash;
}
// Create an authentication cookie that stores the username and a hash of
// the password and salt.
public HttpCookie CreateAuthCookie(string username, string password, string salt)
{
// Create the cookie and set its value to the username and a hash of the
// password and salt. Use a pipe character as a delimiter so we can
// separate these two elements later.
HttpCookie cookie = new HttpCookie("YourSiteCookieNameHere");
cookie.Value = username + "|" + CreateHash(password, salt);
return cookie;
}
// Determine whether the given authentication cookie is valid by
// extracting the username, retrieving the saved password, recomputing its
// hash, and comparing the hashes to see if they match. If they match,
// then this authentication cookie is valid.
public bool IsValidAuthCookie(HttpCookie cookie, string salt)
{
// Split the cookie value by the pipe delimiter.
string[] values = cookie.Value.Split('|');
if (values.Length != 2) return false;
// Retrieve the username and hash from the split values.
string username = values[0];
string hash = values[1];
// You'll have to provide your GetPasswordForUser function.
string password = GetPasswordForUser(username);
// Check the password and salt against the hash.
return IsMatchingHash(password, salt, hash);
}

Answer 2

I would not store the users password in a cookie... Rather store the user id and the ip address in the cookie.

Answer 3

I would not store the ip / user id in the cookie. Session highjacking would then be really easy, I mean I know the username / ip of my collegues, I could add that cookie to my message and then I can work on the session of my collegue.