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Fast secured speech transmission is certainly essential especially in real-time multimedia applications. This paper proposes an effective, low complexity, Selective On-Fly Scrambling Algorithm (SOFSA) that could be implemented on Code-Excited-Linear-Prediction (CELP) parameters while processing the speech frame in order to provide fast speech security. ITU G.723.1, which is one of the most widely used speech coders in Voice over Internet Protocol (VoIP) applications, is chosen as our test CELP coder. Subjective and objective measurements are used to prove SOFSA's utility in real-time voice applications. Results show that the implementation of SOFSA on selective CELP parameters, especially on high intelligibility density parameters, provides a form of data security without compromising neither the bandwidth of the output nor the speech quality. Thereby the proposed algorithm SOFSA could avoid the use of a separate complex data encryption algorithm with higher processing delay.