Method for transmitting digital information safely in GSM voice channel

The invention discloses a method for transmitting digital information safely and reliably in a GSM voice channel. According to the method, the problems that the transmission rate is low, antijamming capability is poor and security is low when digital information is transmitted in the GSM voice channel. The method includes the implementation steps that (1) digital information to be transmitted safely is encrypted through a sending terminal A by the adoption of an SM2 encryption algorithm, and (255,179) BCH channel coding is carried out; (2) OFDM modulation is conducted on the coded result, and FFT interpolation upsampling is carried out; (3) data extraction downsampling and OFDM modulation are conducted on signals received by a receiving terminal B; (4) (255.179) BCH channel decoding is carried out on the modulated result, decryption is conducted by the adoption of the SM2 encryption algorithm, and accordingly a secret key plaintext is obtained. The method can improve the transmission rate of the digital information in the GSM voice channel, reduces transmission error codes, can prevent the information from being leaked and can be used for transmitting the digital information in the GSM voice channel.