Storage type passive covert channel method and system using multiple protocols

Abstract

The invention discloses a storage type passive covert channel method and system using multiple protocols, a covert transceiver synchronization mechanism and a reversible data hiding mechanism are designed based on an m sequence, and the appointed m sequence is searched for a network data packet load through a sequence matching method to determine a covert carrier data packet. Calculating an allowable maximum matching fault-tolerant bit r to improve the matching probability of the m sequence; in the fault-tolerant bit r, the hidden sender allows the load to be modified so as to embed hidden data; a hidden receiver searches a hidden carrier through an agreed m sequence, extracts hidden data and recovers a data packet to realize reversible data hiding; a kernel module based on an Openwrt system is designed to realize covert channel construction, and the system can be deployed in equipment such as an intelligent router carrying the Openwrt system. According to the invention, while the capacity and the transmission rate of the covert channel are ensured, relatively low calculation storage resources are consumed, and the method has the anti-flow analysis capability.

Description

Technical Field

[0001] The present invention relates to the field of covert communication for information security, and in particular to a storage-type passive covert channel method and system utilizing multiple protocols. Background Art

[0002] The concept of covert channels was originally proposed by Lampson. Simmons's most classic adversarial model is the prisoner model. Alice and Bob are two prisoners in a jail. They need to plan an escape plan through communication. However, all their communications are monitored by the head guard, Wendy, who will interrupt any suspicious information. Therefore, Alice and Bob need to hide their secret messages within normal communications to evade Wendy's surveillance. Handel et al. extended the prisoner model to network communications. Girling first proposed the concept of network covert channels in 1987. These channels are communications channels that violate security policies and illegally transmit information within legitimate network traffic. Llamas et al. categorize network covert channels based on their construction mechanisms into two categories: storage-type network covert channels and time-type network covert channels.

[0003] In addition to classifying covert channels based on their construction mechanisms, Lucena et al. categorized covert channels based on whether the sender and receiver of the covert channel are the same as those of the public channel. Depending on the position of the covert sender and receiver on the communication path, covert channels can be divided into active and passive covert channels. If the covert sender generates public traffic and embeds covert data, and the covert receiver is the destination of the public traffic, the covert channel is active. If the covert sender embeds covert data using public traffic and the covert receiver is not the destination of the public traffic, the covert channel is passive. In this case, the covert agent modifies the messages transmitted on the communication path to conceal the secret information. The receiving intermediary can choose to restore or discard the original network traffic, thereby deleting the covert data and eliminating traces of the covert channel.

[0004] Most current network covert channels are developed around the active covert channel model, meaning that the sender and receiver of the covert channel are also the sender and receiver of the public channel. This limits the sender and receiver of the covert channel to communication terminal devices, and the choice of covert carrier is often based on the network traffic of a single communication relationship. Because the covert carrier only contains the traffic of one communication relationship, there is no need to pay attention to the network traffic of other communication relationships. This makes it easy for the covert sender and receiver to reach a consensus on the covert carrier and the synchronization requirements are low, greatly reducing the workload for both parties to perceive the existence of covert data packets. In contrast, non-active covert channels use traffic differently from active covert channels because they introduce intermediate node devices with relay functions as the covert subject. In a passive covert channel, since the sender and receiver of the covert channel are located on the network communication path of the open channel, the passive covert channel can use any passing data packet to build a covert channel. This makes the network traffic relationship that can be used by the passive covert channel richer and more complex than that of the active covert channel, and has higher requirements for synchronization between covert entities, but can reduce sensitivity to traffic analysis attacks. By utilizing different protocols, the present invention can also achieve higher bit rates, as well as privacy, anonymity, etc. Summary of the Invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] The present invention proposes a storage-type passive covert channel method using multiple protocols, focuses on the transfer device as the covert subject, and provides a storage-type passive covert channel solution using multiple protocols, which has higher flexibility and concealment.

[0007] Another object of the present invention is to provide a storage-type passive covert channel system utilizing multiple protocols.

[0008] To achieve the above objectives, the present invention provides a storage-type passive covert channel method using multiple protocols, comprising:

[0009] Generate the initial m sequence based on the agreed key between the concealed sender and receiver, and calculate the maximum error-tolerant bit number;

[0010] Covert sender intercepts network data packets of specific protocols;

[0011] The covert sender performs sequence matching on the payload part of the network data packet, searches for the data packet containing the agreed m-sequence as the covert carrier data packet, and embeds the covert data;

[0012] The covert receiver intercepts packets of a specific protocol flowing through the network;

[0013] The covert receiver uses the currently agreed m-sequence to search the packet payload, find the covert carrier, extract the covert data and recover the packet.

[0014] The storage-type passive covert channel method using multiple protocols according to the embodiment of the present invention may also have the following additional technical features:

[0015] In one embodiment of the present invention, the concealed sender and receiver use a fifth-order primitive polynomial and a random number R as an agreed key and calculate the initial m sequence m init ; Use the autocorrelation of the m sequence to calculate the maximum error-tolerant bit number r.

[0016] In one embodiment of the present invention, the covert sender and receiver use the Netfilter framework in the Openwrt system to register the hook function to the POST_ROUTING point to intercept network data packets and directly operate the sk_buff structure of the network data packet to modify the data packet. The intercepted protocol types include DNS, TLS, HTTP, DTLS, QUIC and UDP without upper-layer application protocols.

[0017] In one embodiment of the present invention, the process of searching for the covert carrier is covert channel synchronization, and the covert sender and receiver determine the covert carrier by searching the agreed m-sequence in the network data packet payload.

[0018] In one embodiment of the present invention, the process of embedding and extracting covert data is reversible data hiding. All bits before the second error-tolerant bit r2 appearing in the byte are used as hidden space, and the number of error-tolerant bits allowed is r. covert =r max -r exist +1, embed the hidden data bit by bit until the hidden space or the number of error-tolerant bits r is allowed covert Exhaustion; the number of embedded bits of hidden data and the position of r1 are uncertain, so an extra 1 byte needs to be added to the end of the hidden carrier as an indicator byte to record the length of the hidden data and the position of r1

[0019] In one embodiment of the present invention, both covert channel synchronization and reversible data hiding are implemented in the kernel space during the operation of the sk_buff structure. After embedding or extracting the covert data, the protocol header field needs to be corrected before the data packet is sent normally.

[0020] In one embodiment of the present invention, the covert receiver uses the currently agreed m-sequence to search the data packet payload, find the covert carrier, extract the covert data and recover the data packet, including:

[0021] The hidden receiver extracts the indicator byte from the hidden carrier in the kernel space and obtains the hidden data length and the position of r1 by parsing the indicator byte.

[0022] The covert sender and receiver share the current m-sequence state, and the covert receiver replaces the covert data with the corresponding m-sequence and The bit at is reversed to complete the recovery of the hidden carrier;

[0023] The covert sender modifies the header fields of the packet and forwards it normally.

[0024] To achieve the above-mentioned object, the present invention further provides a storage-type passive covert channel system utilizing multiple protocols, comprising:

[0025] The error-tolerant bit calculation module is used to generate the initial m-sequence based on the agreed key between the concealed sender and receiver, and calculate the maximum error-tolerant bit number;

[0026] The sender data packet interception module is used to conceal the sender from intercepting network data packets of specific protocols;

[0027] The covert data embedding module is used to perform sequence matching on the payload part of the network data packet by the covert sender, find the data packet containing the agreed m sequence as the covert carrier data packet, and embed the covert data;

[0028] A receiver data packet interception module, used to covertly intercept data packets of a specific protocol flowing through the network by the receiver;

[0029] The data packet recovery module is used by the covert receiver to search the data packet payload using the currently agreed m-sequence, find the covert carrier, extract the covert data and recover the data packet.

[0030] The multi-protocol storage-type passive covert channel method and system of the embodiments of the present invention consumes relatively low computing and storage resources while ensuring the covert channel capacity and transmission rate, and has the ability to resist traffic analysis.

[0031] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0033] Figure 1 is a flow chart of a storage-type passive covert channel method using multiple protocols according to an embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of a covert channel synchronization mechanism according to an embodiment of the present invention;

[0035] Figure 3is a schematic diagram of a reversible data hiding mechanism according to an embodiment of the present invention;

[0036] Figure 4 4 is a structural diagram of a storage-type passive covert channel system using multiple protocols according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0039] The following describes a storage-type passive covert channel method and system using multiple protocols according to an embodiment of the present invention with reference to the accompanying drawings.

[0040] Figure 1 FIG. 1 is a flow chart of a storage-type passive covert channel method using multiple protocols according to an embodiment of the present invention. Figure 1 As shown, the method includes:

[0041] S1, generates the initial m sequence based on the agreed key between the hidden sender and receiver, and calculates the maximum error-tolerant bit number.

[0042] Specifically, the hidden sender and receiver agree on (fifth-order primitive polynomial, random number R) as the key to generate the initial m sequence, m init ={a 1+init ,a 2+init ,…,a l+init},0≤k≤31,init=R mod 2 5 ; Calculate the maximum number of error-tolerant bits r. This includes the following steps:

[0043] (1) The m-sequence generated by an n-order primitive polynomial whose initial states are all 1 is denoted as m0 = {a1, a2, a3, ..., a l},l=2 n -1. After the sequence is shifted k times, the m sequence is expressed as: m k ={a 1+k ,a 2+k ,a 3+k ,…,a l+k},0≤k≤l. According to the number of shifts, the m sequence has 2 n -1, the corresponding states in the covert channel synchronization are 2 n -1 search sequence. Here, the present invention adopts a fifth-order primitive polynomial.

[0044] (2) The sender and receiver generate the initial state m of the m sequence based on the key init ,init=random number mod2 n , the hidden sender modifies the network data packet by m init Sequence search matches to find cryptic vectors.

[0045] (3) In order to improve the matching probability, the present invention allows m to be searched for the data load to be matched. k There can be r bits of fault-tolerant space, denoted as The m sequence (01 sequence) has an autocorrelation characteristic, which measures the difference between an m sequence and its k-times shifted sequence m. k The function of the degree of correlation between is the autocorrelation function:

[0046]

[0047] When calculating the autocorrelation function, 1 is usually used to represent 0 and -1 is used to represent 1. Therefore, when a i = = a i+k When a is equal to 1, the product is -1. i When the value is 0,1, the formula can also be expressed as:

[0048]

[0049] in The number of The shift-add property of the m-sequence ensures that the sequence obtained by adding the m-sequence and its shifted sequence modulo 2 is still a shifted sequence of the m-sequence. The balance of the m-sequence ensures that the number of 1s is one more than the number of 0s. Therefore, in the above formula, EU = -1, and the calculation result of the autocorrelation function is:

[0050]

[0051] Now consider when m k The value of the autocorrelation function when r bits are randomly reversed in the sequence (1->0; 0->1).

[0052] Among them, when When randomly reversing 1 bit in the sequence:

[0053] If k = 0, then the corresponding elements after multiplication have l-1 1s and 1 -1 in the l position, so

[0054] If k≠0, then it is necessary to consider that when the number of the inverted result E is 1 more and the number of U is 1 less, EU=1; when the number of the inverted result E is 1 less and the number of U is 1 more, EU=-3:

[0055] Randomly flip 1 bit

[0056] Among them, when When r bits are randomly reversed in the sequence:

[0057] If k = 0, then the corresponding elements after multiplication have lr 1s and r -1s in the l position, so

[0058] If k≠0, when r zeros are added, EU=-1+2r; when r ones are added, EU=-1-2r:

[0059] Randomly flip r bits

[0060] when Right now When R r (0) is greater than R r (k≠0), that is, there is still a certain degree of autocorrelation when r bits are not considered in the m sequence. The present invention considers that the covert sender and receiver agree to use different m sequences when constructing a covert channel with multiple other covert entities at the same time. Therefore, once r exceeds the threshold, m0 and matches the situation, which makes 2 n -1 m-sequence is no longer unique, and conflicts may occur between various covert channels, leading to synchronization failure. The present invention uses a fifth-order primitive polynomial, so r=7.

[0061] S2, the covert sender intercepts network data packets of a specific protocol.

[0062] Specifically, the covert sender and receiver utilize the Netfilter framework in the Openwrt system, registering a hook function to the POST_ROUTING point to intercept network packets of specific protocols, and then directly manipulate the sk_buff structure of the network packet to modify the packet. The intercepted protocol types include DNS, TLS, HTTP, DTLS, QUIC, and UDP without upper-layer application protocols. In the present invention, the reversible data hiding algorithm modifies the payload of the transport layer protocol packet. Therefore, inappropriate modifications will destroy the syntax and semantics of the upper-layer protocol. In order to minimize the non-compliance of the syntax and semantics of the application layer protocol caused by the modification of the packet, the network protocols and covert embedding areas selected by the present invention are shown in Table 1.

[0063] Table 1

[0064]

[0065] S3, the covert sender performs sequence matching on the payload part of the network data packet, searches for the data packet containing the agreed m sequence as the covert carrier data packet, and embeds the covert data.

[0066] It can be understood that the process of searching for the covert carrier is covert channel synchronization, and the covert sender and receiver determine the covert carrier by searching the agreed m-sequence in the network data packet payload.

[0067] (1) See Figure 2 ,The hidden sender performs byte-by-byte sequence matching on the payload part of the data packet and searches for the m-sequence currently agreed by both parties within the r-bit tolerance range to find the hidden carrier;

[0068] (2) See Figure 3 After finding the hidden carrier, embed the hidden data. In step 1, the r-bit error-tolerant space is calculated using the autocorrelation of the m sequence to increase the probability of finding the hidden carrier. In each hidden carrier C, there is in r exist Often the limit value is not reached. All bits before the second error-tolerant bit r2 appearing in the byte array are used as the hidden space. For r2 The position in

[0069] When r2 does not exist, In the hidden space C covert The allowable number of error-tolerant bits is r covert =r max -r exist +1, at this time the present invention will hide the data Bitwise embedding until the latent space C covert or the number of available fault tolerance bits r covert Exhausted, so the number of hidden data bits that can be hidden by a covert carrier is C available_bit The calculation can be expressed as:

[0070]

[0071] (3) Since the number of embedded bits of the hidden data and the position of r1 are uncertain, an extra byte needs to be added to the end of the hidden carrier as an indicator byte to record the length of the hidden data and the position of r1. The length is 4 bits.

[0072] (4) Embed hidden data into the network data packet payload in kernel space and append indicator bytes, modify the data packet header and send the data packet.

[0073] S4, the covert receiver intercepts packets of a specific protocol flowing through the network.

[0074] Specifically, similar to step S2, the hidden receiver uses the Netfilter framework to intercept network data packets of a specific protocol.

[0075] S5, the covert receiver uses the currently agreed m-sequence to search the packet payload, finds the covert carrier, extracts the covert data and recovers the packet.

[0076] Specifically, the following steps may be included:

[0077] (1) The hidden receiver extracts the indicator byte in the hidden carrier in the kernel space and obtains the hidden data length and the position of r1 by parsing the indicator byte.

[0078] (2) The covert sender and receiver share the current m-sequence state, so the covert receiver replaces the covert data with the corresponding m-sequence and The bit at is reversed to complete the recovery of the hidden carrier.

[0079] (3) The hidden sender modifies the header field of the data packet and forwards it normally.

[0080] It is understandable that both covert channel synchronization and reversible data hiding mechanisms occur in the kernel space when operating on the sk_buff structure. After embedding or extracting covert data, the protocol header field needs to be corrected before the data packet is sent normally.

[0081] According to the embodiment of the present invention, the storage-type passive covert channel method using multiple protocols allows the construction of covert channels through intermediate node devices such as routers, and utilizes traffic with multiple protocols and multiple communication relationships, which greatly reduces the sensitivity of traffic analysis, avoids the aggregation of traffic characteristics of a single end-to-end path, and significantly improves the anti-correlation analysis capability; it has low consumption of computing and storage resources and is suitable for devices with low computing resources such as the Internet of Things; and provides more powerful and flexible covert services.

[0082] In order to implement the above embodiment, Figure 4 As shown, this embodiment also provides a storage-type passive covert channel system 10 using multiple protocols, including:

[0083] The error-tolerant bit calculation module 100 is used to generate an initial m-sequence based on the agreed key between the concealed sender and receiver, and calculate the maximum error-tolerant bit number;

[0084] The sender data packet interception module 200 is used to conceal the sender from intercepting network data packets of a specific protocol;

[0085] The covert data embedding module 300 is used to perform sequence matching on the payload part of the network data packet by the covert sender, search for the data packet containing the agreed m-sequence as the covert carrier data packet, and embed the covert data;

[0086] The receiving-side data packet interception module 400 is used to covertly intercept data packets of a specific protocol flowing through the network at the receiving-side;

[0087] The data packet recovery module 500 is used for the concealed receiver to search the data packet payload using the currently agreed m-sequence, find the concealed carrier, extract the concealed data and recover the data packet.

[0088] According to the embodiment of the present invention, the storage-type passive covert channel system using multiple protocols allows the construction of covert channels through intermediate node devices such as routers, and utilizes traffic with multiple protocols and multiple communication relationships, which greatly reduces the sensitivity of traffic analysis, avoids the aggregation of traffic characteristics of a single end-to-end path, and significantly improves the anti-correlation analysis capability; it consumes less computing and storage resources and is suitable for more types of devices, such as devices with low computing resources such as the Internet of Things; and provides more powerful and flexible covert services.

[0089] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0090] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

Claims

1. A storage-type passive covert channel method using multiple protocols, characterized in that: include: Generate the initial m sequence based on the agreed key between the concealed sender and receiver, and calculate the maximum error-tolerant bit number; Covert sender intercepts network data packets of specific protocols; The covert sender performs sequence matching on the payload part of the network data packet, searches for the data packet containing the agreed m-sequence as the covert carrier data packet, and embeds the covert data; The covert receiver intercepts packets of a specific protocol flowing through the network; The covert receiver uses the currently agreed m-sequence to search the packet payload, find the covert carrier, extract the covert data and recover the packet.

2. The method according to claim 1, characterized in that The concealed sender and receiver use the fifth-order primitive polynomial and the random number R as the agreed key and calculate the initial m sequence m init ; Use the autocorrelation of the m sequence to calculate the maximum error-tolerant bit number r.

3. The method according to claim 1, characterized in that The sender and receiver covertly use the Netfilter framework in the Openwrt system to register the hook function to the POST_ROUTING point to intercept network data packets and directly operate the sk_buff structure of the network data packet to modify the data packet. The intercepted protocol types include DNS, TLS, HTTP, DTLS, QUIC and UDP without upper-layer application protocols.

4. The method according to claim 1, wherein The process of finding the covert carrier is covert channel synchronization. The covert sender and receiver determine the covert carrier by searching the agreed m-sequence in the network data packet payload.

5. The method according to claim 1, wherein The process of embedding and extracting hidden data is called reversible data hiding. All bits before the second error-tolerant bit r2 appearing in the byte are used as hidden space, and the number of error-tolerant bits allowed is r. covert =r max -r exist +1, embed the hidden data bit by bit until the hidden space or the number of error-tolerant bits r is allowed covert Exhaustion; the number of embedded bits of hidden data and the position of r1 are uncertain, so an extra 1 byte needs to be added to the end of the hidden carrier as an indicator byte to record the length of the hidden data and the position of r1 6. The method according to claim 1, characterized in that Covert channel synchronization and reversible data hiding, both of these mechanisms occur in the kernel space when operating on the sk_buff structure. After embedding or extracting covert data, the protocol header fields need to be corrected before the data packet is sent normally.

7. The method according to claim 1, characterized in that The covert receiver uses the currently agreed m-sequence to search the packet payload, find the covert carrier, extract the covert data and recover the packet, including: The hidden receiver extracts the indicator byte from the hidden carrier in the kernel space and obtains the hidden data length and the position of r1 by parsing the indicator byte. The covert sender and receiver share the current m-sequence state, and the covert receiver replaces the covert data with the corresponding m-sequence and The bit at is reversed to complete the recovery of the hidden carrier; The covert sender modifies the header fields of the packet and forwards it normally.

8. A storage-type passive covert channel system utilizing multiple protocols, characterized in that: include: The error-tolerant bit calculation module is used to generate the initial m-sequence based on the agreed key between the concealed sender and receiver, and calculate the maximum error-tolerant bit number; The sender data packet interception module is used to conceal the sender from intercepting network data packets of specific protocols; The covert data embedding module is used to perform sequence matching on the payload part of the network data packet by the covert sender, find the data packet containing the agreed m sequence as the covert carrier data packet, and embed the covert data; A receiver data packet interception module, used to covertly intercept data packets of a specific protocol flowing through the network by the receiver; The data packet recovery module is used by the covert receiver to search the data packet payload using the currently agreed m-sequence, find the covert carrier, extract the covert data and recover the data packet.

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