public static string VerifyCookie(string input, out long signTime, IPAddress remoteIp = null, uint validTime = uint.MaxValue)
{
if (hmacKey == null)
{
throw new InvalidOperationException();
}
signTime = long.MinValue;
if (input == null)
{
return(null);
}
if (input.Length < 80) //Minimum length (60 byte sig+metadata)
{
return(null);
}
if ((input.Length & 3) != 0) //Length of a base64 string must be of multiples of 4
{
return(null);
}
try {
var data = Convert.FromBase64String(input.Replace('.', '+').Replace('_', '/').Replace('-', '=')); //throws FormatException
var computed = hmac.Value.ComputeHash(data, SigLength, data.Length - SigLength); //Compute signature
int trash = 0;
for (int i = 0; i < SigLength; i++) //Compare the sig. (Avoiding timing attack)
{
trash |= data[i] ^ computed[i];
}
if (trash != 0) //sig mismatch, reject.
{
return(null);
}
signTime = data.GetInt64(TsOffset);
var currentTs = UnixTimestamp.CurrentMillisecondTimestamp;
if (signTime > currentTs) //Reject anything with a timestamp from the future
{
return(null);
}
//Compute the validity period for this verification.
//Subtract 1 to treat value 0 (defined as infinite) as greatest.
validTime = Math.Min(data.GetUInt32(ValidityOffset) - 1, validTime - 1);
if (validTime != uint.MaxValue)
{
if ((signTime + validTime) < currentTs) //Should be <=, but we've subtracted 1 from the original value.
{
return(null);
}
}
//all zeroes denotes don't care.
if (!data.TrueForRange(IpAddrOffset, IpAddrLength, x => x == 0))
{
if (remoteIp == null) //No remote ip provided while a verification is required, reject.
{
return(null);
}
if (remoteIp.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
{
remoteIp = remoteIp.MapToIPv6();
}
var ip = remoteIp.GetAddressBytes();
if (!ArrayEx.RangeEquals(data, IpAddrOffset, ip, 0, IpAddrLength))
{
return(null);
}
}
return(cookieEncoding.GetString(data, DataOffset, data.Length - DataOffset)); //throws ArgumentException
} catch (FormatException) {
return(null);
} catch (ArgumentException) {
return(null);
}
}