System for encoding encryption/decryption information into IFF challenges

An encryption system for producing a binary waveform with a predetermined number of bits, the system including:

• A. means for appending n information remaining bits to an m-bit message to form an (m+n)-bit code word;
• B. means for encrypting the code word to produce an (m+n)-bit encrypted code word;
• C. means for selecting m bits of the encrypted code word and inserting between adjacent bits of the m selected bits an anti-interference pulse that is a one if the adjacent bits are two zero-valued bits and an anti-interference pulse that is a zero if the adjacent bits are other than two zero-valued bits;
• and
• D. means for replacing n selected anti-interference pulses with n information pulses, which n information pulses include the n remaining bits of the encrypted code word that are not the m selected bits.

An identification friend or foe system for producing as a binary waveform a challenge with a predetermined number of bits, the system including:

• A. means for formulating and encrypting an m-bit message to produce an m-bit encrypted message;
• B. means for inserting between adjacent bits of the m-bit encrypted message an anti-interference pulse that represents a one if the adjacent bits are two zero-valued bits and represents a zero if the adjacent bits are other than two zero-valued bits;
• and
• C. means for replacing one or more selected anti-interference pulses with a corresponding number of information pulses, the information pulses including information that is used to decipher the encrypted message.

A method of producing a challenge with a predetermined number of bits, the method including the steps of:

• A. encrypting an m-bit message in accordance with a selected cryptographic key to produce an m-bit encrypted message;
• B. inserting between adjacent bits of the m-bit encrypted message an anti-interference pulse that represents a one if the adjacent bits are two zero-valued bits and represents a zero if the adjacent bits are other than two zero-valued bits;
• and
• C. replacing one or more selected anti-interference pulses with a corresponding number of information pulses, the information pulses including information that relates to the decrypting the message.

A method of producing a challenge with a predetermined number of bits, the method including the steps of:

• A. appending n information bits to an m-bit message to form an (m+n)-bit code word;
• B. encrypting the code word to produce an (m+n)-bit encrypted code word;
• C. selecting m bits of the encrypted code word and inserting between adjacent bits an anti-interference pulse that is a one if the adjacent bits are two zero-valued bits and an anti-interference pulse that is a zero if the adjacent bits are other than two zero-valued bits;
• and
• D. replacing n selected anti-interference pulses with n information pulses, which n information pulses include the n remaining bits of the encrypted code word that are not the m selected bits.