A method for spectral and temporal stealthy transmission of information over an optical communication channel, comprising: At the transmitting side: a) reducing the power spectral density PSD of a pulse sequence bearing said information by encrypting the temporal phase of said pulse sequence, thereby preventing the coherent addition of the frequency conversion of the temporal pulses of said pulse sequence in the frequency domain; b) spreading the power of the signal resulting from step a, in the frequency domain, to be below the noise level, by sampling the temporally phase-encrypted pulse sequence by means of a sampler; c) performing spectral phase encoding to temporally spread the pulse sequence resulting from step b and to prevent coherent addition of its spectral replicas in the frequency domain; d) transmitting the signal resulting from step c, encrypted both in time and frequency domains, such that the transmitted signal is below the noise level in both domains; at the receiving side: e) performing spectral phase decoding of a received signal corresponding to said transmitted signal; f) performing coherent detection of the signal resulting from step e; g) folding all the spectral replicas of the signal resulting from step f to the baseband by means of sampling, thereby coherently adding all its spectral replicas at the baseband and reinforcing its PSD; h) decrypting the temporal phase of the signal resulting from step g, thereby coherently adding its temporal pulses at the baseband and reconstructing its PSD and i) using a decision unit, recovering said information from the signal resulting from step h. At the transmitting side: a) reducing the power spectral density PSD of a pulse sequence bearing said information by encrypting the temporal phase of said pulse sequence, thereby preventing the coherent addition of the frequency conversion of the temporal pulses of said pulse sequence in the frequency domain; b) spreading the power of the signal resulting from step a, in the frequency domain, to be below the noise level, by sampling the temporally phase-encrypted pulse sequence by means of a sampler; c) performing spectral phase encoding to temporally spread the pulse sequence resulting from step b and to prevent coherent addition of its spectral replicas in the frequency domain; d) transmitting the signal resulting from step c, encrypted both in time and frequency domains, such that the transmitted signal is below the noise level in both domains; a) reducing the power spectral density PSD of a pulse sequence bearing said information by encrypting the temporal phase of said pulse sequence, thereby preventing the coherent addition of the frequency conversion of the temporal pulses of said pulse sequence in the frequency domain; b) spreading the power of the signal resulting from step a, in the frequency domain, to be below the noise level, by sampling the temporally phase-encrypted pulse sequence by means of a sampler; c) performing spectral phase encoding to temporally spread the pulse sequence resulting from step b and to prevent coherent addition of its spectral replicas in the frequency domain; d) transmitting the signal resulting from step c, encrypted both in time and frequency domains, such that the transmitted signal is below the noise level in both domains; at the receiving side: e) performing spectral phase decoding of a received signal corresponding to said transmitted signal; f) performing coherent detection of the signal resulting from step e; g) folding all the spectral replicas of the signal resulting from step f to the baseband by means of sampling, thereby coherently adding all its spectral replicas at the baseband and reinforcing its PSD; h) decrypting the temporal phase of the signal resulting from step g, thereby coherently adding its temporal pulses at the baseband and reconstructing its PSD and i) using a decision unit, recovering said information from the signal resulting from step h. e) performing spectral phase decoding of a received signal corresponding to said transmitted signal; f) performing coherent detection of the signal resulting from step e; g) folding all the spectral replicas of the signal resulting from step f to the baseband by means of sampling, thereby coherently adding all its spectral replicas at the baseband and reinforcing its PSD; h) decrypting the temporal phase of the signal resulting from step g, thereby coherently adding its temporal pulses at the baseband and reconstructing its PSD and i) using a decision unit, recovering said information from the signal resulting from step h.