Digital voice-band spectrum inversion apparatus

Apparatus for encrypting a plain-text input analog voice-band signal or for decrypting an input analog voice-band signal encrypted by said apparatus, said apparatus comprising:

• means for converting an input analog signal to a digital signal including means for periodically sampling the voltage level of said input analog signal, and means for converting said sampled voltage levels to digital representations thereof;
• means for modifying said digital signal in accordance with an algorithm which computes the two's complement inversion of the digital representations of alternate samples of said input analog signal;
• and
• means for converting said modified digital signal to an output analog signal, said output analog signal being modified in frequency spectrum from said input analog signal.

Apparatus for use in a voice communications system for encrypting a local voice signal or for decrypting a received analog voice-band signal encrypted by said apparatus, said apparatus comprising:

• means for converting an input analog signal to a digital signal including means for periodically sampling the voltage level of said input analog signal, and means for converting said sampled voltage levels to digital representations thereof;
• means for modifying said digital signal in accordance with an algorithm which computes the two's complement inversion of the digital representations of alternate samples of said input analog signal;
• and
• means for converting said modified digital signal to an output analog signal, said output analog signal being modified in frequency spectrum from said input analog signal.

Apparatus for decrypting an input analog voice-band signal which has been encrypted from a plain-text analog signal by frequency spectrum inversion, said apparatus comprising:

• means for converting said input analog signal to a digital signal including means for periodically sampling the voltage level of said input analog signal, and means for converting said sampled voltage levels to digital representations thereof;
• means for modifying said digital signal in accordance with an algorithm which computes the two's complement inversion of the digital representations of alternate samples of said input analog signal;
• and
• means for converting said modified digital signal to an output analog signal.

A method for modifying the frequency spectrum of an input analog voice-band signal comprising the steps of:

• converting said input analog signal to a digital signal by periodically sampling the voltage level of said input analog signal, and converting said sampled voltage levels to digital representations thereof;
• modifying said digital signal by computing the two's complement inversion of the digital representations of alternate samples of said input analog signal;
• and
• converting said modified digital signal to an output analog signal, said output analog signal being modified in frequency spectrum from said input analog signal.