Password Hashing in .NET Core - Full Implementation

PasswordHasher.cs

public sealed class PasswordHasher : IPasswordHasher
{
  private const int SaltSize = 16; // 128 bit 
  private const int KeySize = 32; // 256 bit

  public PasswordHasher(IOptions<HashingOptions> options)
  {
    Options = options.Value;
  }

  private HashingOptions Options { get; }

  public string Hash(string password)
  {
    using (var algorithm = new Rfc2898DeriveBytes(
      password,
      SaltSize,
      Options.Iterations,
      HashAlgorithmName.SHA512))
    {
      var key = Convert.ToBase64String(algorithm.GetBytes(KeySize));
      var salt = Convert.ToBase64String(algorithm.Salt);

      return $"{Options.Iterations}.{salt}.{key}";
    }
  }

  public (bool Verified, bool NeedsUpgrade) Check(string hash, string password)
  {
    var parts = hash.Split('.', 3);

    if (parts.Length != 3)
    {
      throw new FormatException("Unexpected hash format. " + 
        "Should be formatted as `{iterations}.{salt}.{hash}`");
    }

    var iterations = Convert.ToInt32(parts[0]);
    var salt = Convert.FromBase64String(parts[1]);
    var key = Convert.FromBase64String(parts[2]);

    var needsUpgrade = iterations != Options.Iterations;

    using (var algorithm = new Rfc2898DeriveBytes(
      password,
      salt,
      iterations,
      HashAlgorithmName.SHA512))
    {
      var keyToCheck = algorithm.GetBytes(KeySize);

      var verified = keyToCheck.SequenceEqual(key);

      return (verified, needsUpgrade);
    }
  }
}