     /// - throws: A `Generator.Error` if a valid counter cannot be calculated.
     /// - returns: The counter value needed to generate the password for the target time.
     @warn_unused_result
-    internal static func counterWithFactor(factor: Factor, atTimeIntervalSince1970 timeInterval: NSTimeInterval) throws -> UInt64 {
+    private static func counterWithFactor(factor: Factor, atTimeIntervalSince1970 timeInterval: NSTimeInterval) throws -> UInt64 {
         switch factor {
         case .Counter(let counter):
             return counter

    }

    @warn_unused_result
    internal static func validateFactor(factor: Generator.Factor) -> Bool {
        switch factor {
        case .Counter:
            return true

    /// - parameter algorithm:  A generator's algorithm.
    /// - returns: A tuple of a CommonCrypto hash algorithm and the corresponding hash length.
    @warn_unused_result
    private static func hashInfoForAlgorithm(algorithm: Algorithm) -> (algorithm: CCHmacAlgorithm, length: Int) {
        switch algorithm {
        case .SHA1:
            return (CCHmacAlgorithm(kCCHmacAlgSHA1), Int(CC_SHA1_DIGEST_LENGTH))
