CN101771530B - Covert communication method for concealing weighted signal by using common signal sequence - Google Patents

Abstract

The invention discloses a covert communication method for concealing weighted signal by using common signal sequence, relating to the technical field of communication and solving the problems in the prior art that additional noise conceals covert communication during secret information loading in signal wave form domain when adopting four-item weighted score Fourier transform to perform covert communication, and that secret information is easy to discover by an unobjective host. The communication method in the invention comprises: taking a signal of a common sequence after modulation by a base band as a cover signal, modulating covert secrete information by the base band, encrypting by adopting four-item weighted score Fourier transform, implanting the encrypted cover signal into the cover signal to finish information covert communication, when the receiver and the transmitter are synchronous, demodulating the received signal and then subtracting the cover signal to obtain a covert information sequence, and performing four-item weighted score Fourier inversion to obtain corresponding covert information. The invention is extensively applicable in the technical field of covert communication.

Description

A kind of concealed communication method that utilizes general burst to hide weighted signal

Technical field

The present invention relates in general burst, embed weighted signal, belong to communication technical field to reach the implementation method of covert communications.

Background technology

Information Hiding Techniques be the mid-90 in 20th century from external rise, it is the emerging technology that integrates multidisciplinary theory and technology, and has caused professional person's research interest rapidly.It is to utilize the mankind sensory insensitive; And the redundancy of multimedia digital signal existence itself; Secret information is hidden in the host signal, is not discovered or be not noted, and do not influence the sensory effect and the practical value of host signal by people's sensory perceptual system.The Information hiding most important character is that it has not only hidden the content of information, and has hidden the existence of information, thereby demonstrates more excellent characteristic at information security field.

Information hiding is a kind of means of information protection, and it is different from traditional cryptological technique.Cryptographic technique mainly is to study how confidential information to be carried out special coding, to form unrecognizable password form (ciphertext); And Information hiding mainly studies and how a certain confidential information secret is hidden in another disclosed information, and the transmission through public information comes the transfer machine confidential information then

The covert communications technology is an important branch of Information Hiding Techniques, and it is conceived to hide once the existence of communication, that is to say, is to make the uncertain secret that where exists of assailant, and what it was hidden is the form that information exists.As far as coded communication because ciphertext recognized easily, possibly more can evoke the desire that the interceptor decodes, make they intercept and capture ciphertext just all one's effort decode, or redispatch after ciphertext destroyed, thereby influence the safety of confidential information; But as far as the covert communications technology; Seem few owing to hidden the signal of secret information with general signal difference; The interceptor is difficult to judge in the face of numerous information which contains secret information, and which does not have secret information, thereby flees from interceptor's attack relatively easily; Thereby can guarantee the safety of confidential information, reach the purpose of covert communications.

(Fractional Fourier Transform is a kind of important time frequency analyzing tool FRFT) to fractional Fourier transform, has obtained comparatively extensive studies in the last few years, and is able to use in some field of engineering technology.FRFT is the popularization to traditional F ourier conversion, and its essential characteristics is appreciated that and is the fractionation to Fourier transform characteristics value.The continuity of parameter value, rotation additivity and be the fundamental property of FRFT to the uniformity of signal time-frequency form.Owing to, and, make FRFT have various definition form to the wide in range property that FRFT character retrains to the difference of characteristic value fractionation mode.According to these definition starting point and essential characteristic separately, can roughly it be divided into two types, that is: classical type FRFT and weighting class FRFT.

Classical type FRFT is a kind of FRFT form that proposes relatively early, and it directly from Fourier transform integrals nuclear and characteristic value, is promoted with complete.Because the orthogonal basis of classical FRFT with chirp form, thereby the classical type FRFT chirp class FRFT that is otherwise known as.Research and application about FRFT at present concentrates on classical type mostly, because morning, research appear extensively, thereby also it directly is called FRFT sometimes.Classical FRFT has application more widely in finding the solution scientific researches such as the differential equation, quantum mechanics, signal analysis and processing; The engineering aspect is to utilize classical FRFT the earliest like optical correlation fields such as optical communication system, light image processing, also is that application is the most successful at present.But be subject to the discrete logarithm problem of classical FRFT, its application in the communications field has received bigger restriction.

Weighting class fractional Fourier transform (Weighted FRFT is a kind of new mathematical tool that is different from classical fractional Fourier transformation WFRFT), propose first in nineteen ninety-five by C.C.Shih, classical type evening many.Propose beginning, it only defines in order to satisfy the FRFT fundamental property, and conversion itself is not endowed the actual physical meaning.Along with the progress of optical research, the mathematical property of WFRFT has obtained good embodiment in optical system, and can realize through simple optics, thereby in Information Optics, is able to use widely.

After C.C.Shih, to go deep into along with what FRFT was studied, the definition of WFRFT is constantly promoted, and unified with classical FRFT to a certain extent.The WFRFT definition form that C.C.Shih proposed goes for any periodic conversion that has.Utilize this character, can continuous WFRFT definition be generalized to the WFRFT of discrete series.

Four-item weight score Fourier conversion (4-WFRFT) that tradition is continuous is defined as:

F ^α[f](t)＝w ₀(α)f(t)+w ₁(α)F(t)+w ₂(α)f(-t)+w ₃(α)F(-t)

W wherein ₀～w ₃Be the weight coefficient by the control of dynamic encryption parameter alpha, the form of embodying is:

$w_l\left(\mathrm{\α}\right)=\cos \left(\frac{(\mathrm{\α}-l)\mathrm{\π}}{4}\right)\cos \left(\frac{2(\mathrm{\α}-l)\mathrm{\π}}{4}\right)\exp (\±\frac{3(\mathrm{\α}-l)\mathrm{\πi}}{4}),(l=\mathrm{0,1,2,3})$

The value cycle of dynamic encryption parameter alpha is 4, and the span of setting α here is any real number between [0,4] or [2,2], for the real number outside the span, and weight coefficient α _l(l=0,1,2,3)

Will be along with α presents cyclic variation.The result of four-item weight score Fourier conversion is f (t) when α=0, and the result of four-item weight score Fourier conversion is F (t) when α=1.Wherein f (t) is by the function of conversion, and f (is the counter-rotating function at center with the initial point for f (t) t); F (t) becomes the right function of Fourier transform with f (t), and F (is the counter-rotating function at center with the initial point for F (t) t).Definition below Fourier transform adopts:

$X\left(\mathrm{\&omega;}\right)=\frac{1}{\sqrt{2\mathrm{\&pi;}}}\underset{-\&infin;}{\overset{\&infin;}{\&Integral;}}x\left(t\right)e^{-\mathrm{j\&omega;t}}\mathrm{dt},-\&infin;<\mathrm{\&omega;}<\&infin;$

The definition of the four-item weight score Fourier conversion (4-WFRFT) of discrete series is as follows after promoting:

F ^α，V[x(n)]＝w ₀(α，V)x(n)+w ₁(α，V)X(n)+w ₂(α，V)x(-n)+w ₃(α，V)X(-n)

Wherein

$w_l(\mathrm{\&alpha;},m_k,n_k)=\frac{1}{4}\underset{k=0}{\overset{3}{\mathrm{\&Sigma;}}}\exp \{\&PlusMinus;\frac{2\mathrm{\&pi;i}}{4}[(4m_k+1\left(\mathrm{\&alpha;}\right)k+{4n}_k)-\mathrm{lk}\left]\right\}l=\mathrm{0,1,2,3}.$

Be by curtain V=[m ₀, m ₁, m ₂, m ₃] and NV=[n ₀, n ₁, n ₂, n ₃] wait the common weight coefficient form of controlling of 9 parameters, wherein MV and NV are real vector, make V=[MV, NV].X (n) and x (n) be DFT (DFT) to (through substitution of variable n=k), DFT adopts following formal definition:

$\left\{\begin{array}{c}X\left(k\right)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}x\left(n\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H201010300718420100126E000021.png,H201010300718420100126E000031.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\mathrm{kn}}\\ x\left(n\right)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="H201010300718420100126E000021.png,H201010300718420100126E000031.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\end{array}\right.$

Four-item weight score Fourier conversion after promoting has been inherited all character of former conversion, can come the rotation of the periodicity and the characteristic vector of control change in addition through the adjustment to real vector M V and NV.In a word, the four-item weight score Fourier conversion after promoting is complicated more, but more complete in theory, and is more flexible and changeable during practical application.

It all is the loading of carrying out secret information in the source encoding territory that conventional information is hidden transmission method, and other secret information embedding grammars of describing the territory almost do not relate at signal.The benefit of carrying out the secret information loading in the source encoding territory is can secret information sent and receive with identical load mode with blindage information, and secret information has with blindage information and has equal protection in channel.Problem is that secret information and blindage information are not easily separated, if blindage information is kept by information acquisition person for a long time, then has the found risk of secret information; In addition, owing to secret information and blindage information cutting apart physically not make the cost of detection secret information to exchange for through the time.

The secret information in signal waveform territory loads and extraction needs special-purpose transmission and receiving equipment, can realize the physical segmentation of secret information and blindage information.Do not having under the situation of equipment, secret information will be disposed with the form of noise by general receiver, can't be kept for a long time by information acquisition person.The deficiency that the waveform territory loads is to require higher sensitivity and interference free performance for the purpose receiver, because the common energy of secret information at this moment is less than blindage information, receives the influence of channel more easily.Present employed signal waveform domain information loading technique, a main deficiency need to be the outer noise of plus just can cover the planisphere of covert communications, under the situation of additional noise deficiency, also can improve the risk that covert communications exposes on the other hand.

Summary of the invention

The objective of the invention is for solving existing when adopting four-item weight score Fourier conversion to carry out covert communications; Carry out in the signal waveform territory existing the plus external noise to reach the purpose of covering covert communications when secret information loads; And the problem that exists secret information to be found by non-destination host easily provides a kind of concealed communication method that utilizes general burst to hide weighted signal.The concrete steps of this method are:

Transmitter terminal:

Step 1: with general burst through after the baseband modulation as the blindage signal;

Step 2: the secret information of hiding is hidden signal through acquisition after the baseband modulation;

Step 3: the hiding signal that step 2 is obtained adopts the four-item weight score Fourier transform to encrypt, and obtains weighted signal, and weighted signal is carried out the blindage signal plus that obtains with step 1 behind the amplitude fading, obtains the hiding signal of encrypting;

Step 4: the hiding signal of the encryption that step 3 is obtained through the digital carrier modulation after, after D/A conversion and up-conversion, send into channel again and transmit;

Receiver end:

Step 5: when receiver and transmitter fully synchronously the time, receive signal, and after the signal that receives sampled with A/D through down-conversion, again through the digital carrier demodulation; Obtain restituted signal;

Step 6: after in the restituted signal that step 5 obtains, deducting the blindage signal, adopt the four-item weight score Fourier inversion to decipher, obtain to hide signal, realize covert communications.

The present invention proposes to utilize the covert communications technology to come hiding necessary being of communicating by letter with the protection important information, in order to reduce the probability that important information is intercepted and captured; Utilize general sequence through the signal after the baseband modulation as blindage signal (being also referred to as host signal); Consider confidentiality through the signal after the four-item weight Fourier transform; The important information of desire protection is carried out the four-item weight score Fourier transform earlier, be embedded into then in the blindage signal.When Receiver And Transmitter fully synchronously the time, as long as deduct the blindage signal, just can obtain to pass through accordingly the information sequence after the weighting, process four-item weight score Fourier inversion just can obtain to hide Info accordingly again.Wherein, the key of telescopiny is the conversion exponent number, and the key of leaching process is corresponding inverse transformation exponent number, and the encryption measures that hides Info is the four-item weight score Fourier transform.

Beneficial effect of the present invention: when the inventive method is carried out the information loading of covert communications on the signal waveform territory, can realization information transmit when purpose receiver and transmitter are synchronous, do not need the outer noise signal of plus.Secret information to be passed is embedded in the blindage signal through after the weighted transformation, has strengthened the non-correlation between the signal, protected secret information effectively.Even the blindage signal is intercepted and captured by the enemy, do not carry out coded communication owing to do not understand which kind of mode of employing, therefore also be difficult to deciphering.Secret information through behind the weighted transformation again with the blindage signal plus, more reduced the probability that information comes to light and is decrypted.

Description of drawings

Fig. 1 utilizes general burst to hide the signal processing flow sketch map of the covert communications of weighted signal; Fig. 2 is the planisphere of blindage signal of the present invention; Fig. 3 is through the hiding signal constellation which after the 0.5 rank four-item weight score Fourier transform, and Fig. 4 is the planisphere of blindage signal behind the hiding secret information of employing the inventive method embedding.

Embodiment

Embodiment one: combine Fig. 1 that this execution mode is described, the described a kind of concealed communication method that utilizes general burst to hide weighted signal of this execution mode.

Its concrete steps are:

Transmitter terminal:

Step 1: with general burst through after the baseband modulation as the blindage signal;

Step 2: the secret information of hiding is hidden signal through acquisition after the baseband modulation;

Step 3: the hiding signal that step 2 is obtained adopts the four-item weight score Fourier transform to encrypt, and obtains weighted signal, and weighted signal is carried out the blindage signal plus that obtains with step 1 behind the amplitude fading, obtains the hiding signal of encrypting;

Step 4: the hiding signal of the encryption that step 3 is obtained through the digital carrier modulation after, after D/A conversion and up-conversion, send into channel again and transmit;

Receiver end:

Step 5: when receiver and transmitter fully synchronously the time, receive signal, and after the signal that receives sampled with A/D through down-conversion, again through the digital carrier demodulation; Obtain restituted signal;

Step 6: after in the restituted signal that step 5 obtains, deducting the blindage signal, adopt the four-item weight score Fourier inversion to decipher, obtain to hide signal, realize covert communications.

Referring to Fig. 2, Fig. 3 and Fig. 4; Adopt analogue system that the signal in the described communication means of this execution mode is carried out emulation; The blindage signal that said emulation is adopted is the signal that general burst obtains through QPSK base band mapping back; The hiding signal signal that to be secret information obtain through QPSK base band mapping back, hiding signal carry out the weighted signal that obtains behind the 0.5 rank four-item weight score Fourier conversion, and the amplitude fading of said weighted signal is 3dB; From Fig. 3 and Fig. 4, can find out; Weighted signal presents a kind Gauss distribution situation on complex plane; This blindage signal that make to embed behind secret information distributes at complex plane, and said blindage signal is similar to the general signal complex plane distribution situation after the Gaussian noise that superposeed very much, is difficult for causing interceptor's interest like this; The attack of non-destination host can be effectively hidden, good covert communications can be realized.

The described employing four-item weight score of this execution mode step 3 Fourier transform carry out the direct transform exponent number that encrypted secret key is four-item weight score Fourier the definition of said direct transform is following for α, V}:

S ₀＝F ^α，V[X ₀(n)]＝w ₀(α，V)X ₀(n)+w ₁(α，V)X ₁(n)+w ₂(α，V)X ₂(n)+w ₃(α，V)X ₃(n)

The key that the described employing four-item weight score of this execution mode step 6 Fourier inversion is deciphered be four-item weight score Fourier the inverse transformation exponent number definition of said inverse transformation is following for α, V}:

X ₀(n)＝F ^-α，V[S ₀](n)＝w ₀(-α，V)S ₀(n)+w ₁(-α，V)S ₁(n)+w ₂(-α，V)S ₂(n)+w ₃(-α，V)S ₃(n)。

The signal processing flow of this execution mode all can be realized by DSP, FPGA or FPGA and DSP combination.

The present invention utilizes the entrained information of general baseband modulation signal as blindage information, and secret information to be passed as hiding Info, is embedded in the blindage information.Transmitting and receiving under the situation that end is synchronous, embedding is suitable, can cover the fact of secret information transmission, reaching the purpose of covert communications.In order to strengthen the privacy degrees of secret information, secret information has been passed through the four-item weight score Fourier transform, reach planisphere counter-rotating and randomized purpose.Wherein, the key of telescopiny is the exponent number of weighted transformation, and the key of leaching process is corresponding inverse transformation exponent number.

When the present invention adopted four-item weight score Fourier conversion to carry out signal encryption at the unknown transmitter of non-purpose receiver, this method can well be hidden actual signal.And when non-purpose receiver known transmitter adopts four-item weight score Fourier conversion to carry out signal encryption,, having obtained the position of ideal constellation even through up to a hundred detections, it is to carry out wrong demodulation that very big probability is also arranged.Said one-parameter four-item weight score Fourier conversion signal all has the characteristic of multiple Gaussian distribution on time-frequency domain, this statistical property and noise are similar; Multi-parameter four-item weight score Fourier conversion signal has the advantages that constellation separates, and this signal with the process multipath channel has similitude.These two characteristics make the four-item weight score Fourier conversion signal have very strong camouflage property.

Claims (1)

1. concealed communication method that utilizes general burst to hide weighted signal is characterized in that concrete steps are:

Transmitter terminal:

Step 1: with general burst through after the baseband modulation as the blindage signal;

Step 2: the secret information of hiding is hidden signal through acquisition after the baseband modulation;

Step 3: the hiding signal that step 2 is obtained adopts the four-item weight score Fourier transform to encrypt, and obtains weighted signal, and weighted signal is carried out the blindage signal plus that obtains with step 1 behind the amplitude fading, obtains the hiding signal of encrypting;

Step 4: the hiding signal of the encryption that step 3 is obtained through the digital carrier modulation after, after D/A conversion and up-conversion, send into channel again and transmit;

Receiver end:

Step 5: when receiver and transmitter fully synchronously the time, receive signal, and after the signal that receives sampled with A/D through down-conversion, again through the digital carrier demodulation; Obtain restituted signal;

Step 6: after in the restituted signal that step 5 obtains, deducting the blindage signal, adopt the four-item weight score Fourier inversion to decipher, obtain to hide signal, realize covert communications;

The described employing four-item weight score of step 3 Fourier transform carry out the direct transform exponent number that encrypted secret key is four-item weight score Fourier α, V}, being defined as of said direct transform:

S ₀＝F ^α，V[X ₀(n)]＝w ₀(α，V)X ₀(n)+w ₁(α，V)X ₁(n)+w ₂(α，V)X ₂(n)+w ₃(α，V)X ₃(n)；

The key that the said employing four-item weight score of step 6 Fourier inversion is deciphered be four-item weight score Fourier the inverse transformation exponent number α, V}, being defined as of said inverse transformation:

X ₀(n)＝F ^-α，V[S ₀](n)＝w ₀(-α，V)S ₀(n)+w ₁(-α，V)S ₁(n)+w ₂(-α，V)S ₂(n)+w ₃(-α，V)S ₃(n)。

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