Apparatus and method for computer-based or mobile-device-based electronic generation and verification of dynamic password, or one-time-password (OTP), that does not require initial synchronization, nor re-synchronization, between a client OTP generator and the corresponding OTP server, is provided. It employs the general OTP principles and methods to ensure the single-use of the password credential and the security strength of the OTP, and it utilizes instant dynamic parameter(s) communications for equivalent instant synchronization (EQ-sync). It can also be used to ensure integrity and authenticity of an online transaction request.