/// <summary>
/// Compute the PBKDF2 function on the given inputs using the CNG implementation in the <c>BCryptKeyDerivation</c> API.
/// </summary>
/// <param name="hashName">The hash function to use, must be one of the strings in <seealso cref="PBKDF2HashAlgorithm"/>.</param>
/// <param name="password">The password, as a byte array (i.e., without a string termination character).</param>
/// <param name="salt">The salt, a cryptographically random value. Should be 16-bytes or longer.</param>
/// <param name="cIterations">The number of iterations of PBKDF2 to apply.</param>
/// <returns>The digest of the password (also sometimes called derived key). The length of the digest
/// will be equal to the length of the chosen hash function output.</returns>
/// <remarks>
/// See http://msdn.microsoft.com/en-us/library/windows/desktop/hh448506 for a description
/// of the wrapped function. Larger values of cIterations will cause the function to use more
/// CPU time, and will also increase the workfactor for an attacker in a brute-force attack.
/// </remarks>
public static byte[] ComputeHash(string hashName, byte[] password, byte[] salt, Int64 cIterations)
{
if (cIterations < 1)
{
throw new ArgumentException("Iteration count must be greater than zero.", "cIterations");
}
if (salt == null)
{
throw new ArgumentException("Salt must be non-null", "salt");
}
if (password == null)
{
throw new ArgumentException("Password must be non-null", "password");
}
if (!PBKDF2HashAlgorithm.ValidateHashName(hashName))
{
throw new ArgumentException("Invalid hash name for PBKDF2");
}
byte[] digest = null;
double vers = Environment.OSVersion.Version.Major + Environment.OSVersion.Version.Minor * 0.1;
if (vers > 6.1)
{
// The BCryptKeyDerivation API is only supported on Win8/Server 2012 and above
digest = BCryptNative.PBKDF2BCryptKeyDerivation(hashName, password, salt, (UInt64)cIterations);
}
else
{
// Fall back to BCryptDeriveKeyPBKDF2, which is roughly 2x slower on systems without the KeyDerivation API
digest = BCryptNative.PBKDF2BCryptDeriveKeyPBKDF2(hashName, password, salt, (UInt64)cIterations);
}
return(digest);
}
