Merge "Update challenge size check"

        return "Challenge must be a Bstr.";

    }

    if (challenge.size() < 32 || challenge.size() > 64) {

        return "Challenge size must be between 32 and 64 bytes inclusive. "

    if (challenge.size() < 16 || challenge.size() > 64) {

        return "Challenge size must be between 16 and 64 bytes inclusive. "

               "However, challenge is " +

               std::to_string(challenge.size()) + " bytes long.";

    }