A secure communication system utilizes multiple decoy data signals to hide one or more true data signals. The true data signal(s) are encrypted, and received at a scrambling unit according to an original set of channel assignments. The channel assignments are optically switched with multiple decoy data signals to form a multi-channel scrambled output signal that is thereafter transmitted across a communication system. The greater the number of decoy signals, the greater the security provided to the open-air system. Further security may be provided by encrypting the decoy signals prior to scrambling and/or by utilizing a spatially diverse set of transmitters and receivers. Without the knowledge of the channel assignment(s) for the true signal(s), an eavesdropper may be able to intercept (and, with time, perhaps descramble) the open-air transmitted signals, will not be able to distinguish the true data from the decoys without also knowing the channel assignment(s).

A method of securely transmitting data comprising (1) obtaining an unencrypted data stream comprising a first sequence of values, (2) segmenting a first portion of the first sequence of values into an original first word having a word-length equal to a first variable, (3) segmenting a second portion of the first sequence of values into an original second word having a word-length equal to a second variable different than the first variable, (4) inserting random values at predetermined locations in the original first and second words to generate modified first and second words, the modified first and second words having a word-length equal to a third variable different than the first and second variables, and (5) combining the modified first and second words into a second sequence of values defining an encrypted data stream.

A secure communication system utilizes multiple decoy data signals to hide one or more true data signals. The true data signal(s) are encrypted, and received at a scrambling unit according to an original set of channel assignments. The channel assignments are optically switched with multiple decoy data signals to form a multi-channel scrambled output signal that is thereafter transmitted across a communication system. The greater the number of decoy signals, the greater the security provided to the open-air system. Further security may be provided by encrypting the decoy signals prior to scrambling and/or by utilizing a spatially diverse set of transmitters and receivers. Without the knowledge of the channel assignment(s) for the true signal(s), an eavesdropper may be able to intercept (and, with time, perhaps descramble) the open-air transmitted signals, will not be able to distinguish the true data from the decoys without also knowing the channel assignment(s).

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a transmitter device may modify, based at least in part on a secrecy key, an input or an output of at least one of binary scrambling, modulation, or orthogonal frequency division multiplexing (OFDM) tone mapping for a physical control channel signal, resulting in a secured physical control channel signal. The transmitter device may transmit, to a receiver device, the secured physical control channel signal. Numerous other aspects are described.

An apparatus for preventing a relay attack that includes a microcontroller, a receiver, and a transmitter. The receiver is configured to receive a challenge message from a verifier. The challenge message has a challenge message frequency at a first challenge message frequency during a first time slot. The transmitter is configured to transmit a response message to the verifier. The response message has a response message frequency at a first response message frequency during the first time slot. The first response message frequency is different than the first challenge message frequency. The challenge message frequency is at a second challenge message frequency and the response message frequency is at a second response message frequency during a second time slit. The second challenge message frequency is different than the second response message frequency.

A method of transmitting a message using a slow hopping anti-jam waveform, includes generating a sequence with a cryptographic hash function; transmitting, for a predetermined dwell time, a first portion of the message on a first channel having a first baseline frequency; choosing a second channel having a second baseline frequency based on the generated sequence, the second baseline frequency being offset from the first baseline frequency; and transmitting, for the predetermined dwell time, a second portion of the message on the second channel having the second baseline frequency; wherein the two transmitting steps occur sequentially.

A method includes providing a plurality of variables and a variable. The variables differ from each other. The variables differ from the variable. The further method includes providing a lookup table indexing a plurality of characters via a plurality of values based on a first numeral system, converting a message into a first sequence of values based on the table, converting the first sequence into a second sequence of values based on a second numeral system different from the first system and according to a preset format, combining the second sequence into a single sequence via removing the format, generating a first plurality of subsequences from the single sequence based on segmentation of the sequence via alternating the variables, converting the first subsequences into a second plurality of subsequences such that each of the second subsequences is sized according to the variable, and transmitting the second subsequences.

A method for variable length decoding, the method including: receiving, in a default word length mode, at least one first data word having a default first word length; combining the received at least one first data word as a first portion of data; receiving, after the at least one first data word, a transition word indicative of transitioning to a variable word length mode; receiving, after the transition word, a first word length word indicative of a second word length; receiving, after the first word length word, at least one second data word having the second word length; and combining the received at least one second data word as a second portion of the data.

A method for variable length decoding, the method including: receiving, in a default word length mode, at least one first data word having a default first word length; combining the received at least one first data word as a first portion of data; receiving, after the at least one first data word, a transition word indicative of transitioning to a variable word length mode; receiving, after the transition word, a first word length word indicative of a second word length; receiving, after the first word length word, at least one second data word having the second word length; and combining the received at least one second data word as a second portion of the data.

In the area of Joint Random Subcarrier Selection and Channel-Based Artificial Signal Design Aided PLS, a method for providing physical layer security (PLS) depending on the randomness of wireless channel is proposed. Specifically, a channel-based joint random subcarrier selection and artificial signal design are introduced to protect the communication in the presence of a passive eavesdropper which can be even stronger than the legitimate receiver. Our analysis assumes a window-based subcarrier selection method in which the strongest subcarriers in each window are selected. Chosen subcarriers are considered for secret sequence extraction. The generated channel dependent secret sequence is used for both random subcarrier selection and artificial signal design. We evaluate the efficiency of the proposed method through some representative metrics, such as secret sequence disagreement rate (SSDR), throughput and bit error rate (BER), in both perfect and imperfect channel estimation cases. Simulation results are presented and insightful discussions are drawn.