A secure USB flash drive and data security migration system based on DRAM

Abstract

The present invention discloses a DRAM-based secure USB flash drive and a secure data migration system, and belongs to the field of computer information security. The present invention uses DRAM as a USB flash drive storage medium, and its data power-off volatile characteristics can prevent violent disassembly and theft of data in the storage chip, thereby enhancing the data anti-theft capability; through hardware and software implementation methods, the data survival time limit is increased for the secure USB flash drive movement situation (disconnection from the host computer), while strengthening data security management, the risk of data leakage is reduced; through special circuit design, the data erasure function of the secure USB flash drive offline (disconnection from the host computer) is realized, which reduces the exposure of data to the host computer, thereby reducing the chance of data leakage; through the joint design of the secure USB flash drive and the interface of the confidential host computer, the illegal behavior of removing data from the confidential host computer is prevented from the hardware level, which conforms to the confidential environment data management specification and enhances data security.

Description

Technical Field

[0001] The present invention belongs to the field of computer information security, and more specifically, relates to a DRAM-based secure USB flash drive and a data security migration system. Background Art

[0002] In the application scenario of confidential data migration, the main problems are "transferring data from the outside to the confidential environment and preventing the illegal transfer of data from the confidential environment to the outside" and "reliably destroying data to prevent data from being recovered and stolen."

[0003] There are two solutions to the above problems in the prior art: the first solution is CD-ROM, and its main idea is as follows: outside the confidential environment, data is written once by relying on a special writing device, and then read out after entering the confidential environment to complete the data migration work. The feature of supporting only one write can prevent malicious users from writing data to the CD-ROM in the confidential environment and illegally taking it out: relying on a CD shredder, the CD-ROM carrying sensitive information can be destroyed. After being shredded, the data on the CD-ROM cannot be restored, and the data destruction method is reliable. The second solution is a special security USB flash drive for confidential information, and its main idea is as follows: the system uses two major components, software and hardware, to install an agent program on the controlled host and deploy a hardware controller to authorize and audit the USB mobile storage medium of the controlled host, block the possible information leakage channels of the controlled host, and perform physical layer unidirectional control on the transmission of information from the USB mobile storage device to the confidential computer, effectively preventing the confidential information from flowing back into the USB mobile storage device during the information transmission process, and at the same time realizing the necessary functions such as data management and reliable destruction. The advantage of the special security USB flash drive for confidential information is fast reading and writing.

[0004] However, the first solution has the following defects: data burning depends on a specific burning device, data storage is slow and may fail; when destroying data, a shredder must be used to shred the disc to ensure that the data is definitely erased. Operations such as manually scratching the disc surface cannot ensure that the data is completely deleted, and the data destruction efficiency is low; in the security specifications of confidential data migration scenarios, regardless of the size of the file, each data transfer consumes a disc, and it is destroyed after the transfer is successful, resulting in a waste of disc resources; in short, the characteristics of the CD-ROM solution are that security can be guaranteed, but it will reduce unit work efficiency and resource utilization efficiency. The second solution has the following disadvantages: because the device itself is not powered, the device's software system depends on the host computer to operate; if the internal data of the device is to be erased, it cannot be done offline, and the device must be connected to the host computer and then the data is erased byte by byte, but once the U disk device is connected to the host computer, the risk of data leakage is increased; the storage medium of the U disk is a Flash chip, which cannot resist brute force cracking. If the Flash chip is forcibly removed, the data is no longer protected by the software and hardware of the secure U disk, resulting in a huge risk of data leakage. In summary, the existing special security USB flash drives for confidential information are more efficient than CD-ROMs, but their security may not be guaranteed. Summary of the invention

[0005] In view of the defects and improvement needs of the prior art, the present invention provides a DRAM-based secure USB flash drive and a data security migration system, which aims to achieve offline reliable data erasure of the USB flash drive and resist violent demolition and cracking.

[0006] To achieve the above object, according to a first aspect of the present invention, a secure USB flash drive based on DRAM is provided, the secure USB flash drive comprising: a USB interface, a self-powered circuit, a main control chip and a DRAM chip;

[0007] The power line anode of the USB interface is connected to the self-powered circuit, the differential signal line of the USB interface is connected to the main control chip, and the USB interface is used to realize the connection between the secure U disk and the host computer;

[0008] The self-powered circuit is used to convert the voltage provided by the host computer through the USB interface into the working voltage of the main control chip and the DRAM chip when the secure USB flash drive is connected to the host computer, and to supply power to the main control chip and the DRAM chip; when the secure USB flash drive is not connected to the host computer, the self-powered circuit supplies power to the main control chip and the DRAM chip by itself;

[0009] The main control chip is connected to the DRAM chip, and is used for sending a write data request to the main control chip through the USB signal line when the host computer sends data to be written to the secure U disk, and then sending the data to be written to the main control chip. The main control chip encrypts the data to be written and sends it to the DRAM chip for storage; when the host computer reads data from the secure U disk, the host computer sends a read data request to the main control chip, the main control chip requests to read data from the DRAM chip, the DRAM chip sends the ciphertext of the requested data to the main control chip, the main control chip decrypts the received ciphertext of the requested data into plaintext, and sends the plaintext to the host computer through the USB signal line.

[0010] Beneficial effect: The present invention adopts DRAM instead of Flash chip as the U disk storage medium. Once the DRAM chip is taken out by violent cracking, all internal data will be lost in a very short time (100ms) due to the loss of power supply, thereby resisting violent cracking. In addition, the number of erasures and writes of DRAM storage medium is unlimited, and there is a natural huge advantage in the number of erasures and writes compared with traditional storage media, which can save resources to a great extent. During the period when the security U disk is not connected to the host computer, when the voltage provided by the self-powered circuit is the working voltage of the main control chip and the DRAM chip, the data inside the security U disk is valid; when the voltage provided is lower than the working voltage of the main control chip and the DRAM chip, the data inside the security U disk is lost. The present invention realizes the limitation of the survival time of internal data from the hardware level through the self-powered circuit. The stored electricity in the power supply circuit will be consumed during the power supply process, and the voltage will gradually decrease. When the output voltage is lower than the working voltage, the main control chip and the DRAM chip lose power, and the data of the U disk will also be lost, that is, the time limit is added for the use of data, which is conducive to reducing the risk of data leakage and strengthening data security management.

[0011] Preferably, the statistical time starts from 0 from the moment the secure U disk is disconnected from the host computer. If the statistical duration of the secure U disk disconnection exceeds the set threshold, the main control chip cuts off the clock supply and self-refresh command to the DRAM chip. After the DRAM loses the clock and stops self-refreshing, data is lost. During the period when the secure U disk is not connected to the host computer, the self-power supply circuit continues to provide the working voltage of the main control chip and the DRAM chip, and supplies power to the main control chip and the DRAM chip.

[0012] Beneficial effect: The present invention performs software control through the main control chip, so that the data in the DRAM is erased after a certain period of time (the user can set / change the time threshold through the host computer program) after the USB flash drive is disconnected, that is, a time limit is added to the use of the data, which is beneficial to reduce the risk of data leakage and strengthen data security management.

[0013] Preferably, the self-powered circuit comprises: a single-pole double-throw switch, a super capacitor and a linear voltage regulator chip;

[0014] The common end of the single-pole double-throw switch is connected to the anode of the supercapacitor, the first active end is connected to the USB interface, and the second active end is grounded; the anode of the supercapacitor is connected to the common end of the single-pole double-throw switch, and the cathode is grounded; when the secure U disk is connected to the host computer and the single-pole double-throw switch is closed at the first active end, the host computer charges the supercapacitor; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is closed at the first active end, the supercapacitor supplies power to the main control chip and the DRAM chip; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is closed at the second active end, the supercapacitor is short-circuited and discharged, the DRAM chip loses power supply, and the internal data is completely erased;

[0015] The input end of the linear voltage regulator chip is connected to the first active end of the single-pole double-throw switch, and the output end is connected to the main control chip and the DRAM chip. When the input voltage is greater than or equal to the minimum working voltage of the linear voltage regulator chip, the input voltage is stepped down and converted into the working voltage output of the main control chip and the DRAM chip; when the input voltage is less than the minimum working voltage of the linear voltage regulator chip, the working voltage supply of the main control chip and the DRAM chip is cut off.

[0016] Beneficial effect: The present invention realizes a self-powered circuit through a supercapacitor and a linear voltage regulator chip. The self-powered circuit cooperates with a DRAM storage medium. When the security U disk is not connected to a host computer and the single-pole double-throw switch is closed at the second active end, the supercapacitor is short-circuited and discharged. After the DRAM chip loses power, it can ensure that its internal data is completely erased and cannot be restored. This realizes offline and reliable destruction of internal data without relying on a host computer, thereby preventing data leakage.

[0017] Preferably, by adjusting the minimum effective supply voltage of the supercapacitor At least one of the nominal value C of the super capacitor and the system sleep current I in the mobile state is used to adjust the survival time T of the data inside the secure USB flash drive. The above parameters satisfy the following relationship in, It indicates the initial potential of the supercapacitor built into the mobile power supply module when it is removed.

[0018] Preferably, the self-powered circuit further comprises: a first voltage-dividing resistor, a second voltage-dividing resistor and a switching diode;

[0019] The first voltage-dividing resistor and the second voltage-dividing resistor are connected in series between the anode of the USB interface and the ground, and are used to convert the voltage level on the USB power line into a level compatible with the working voltage of the main control chip, wherein one end of the second voltage-dividing resistor is directly connected to the ground;

[0020] Assume that the resistance of the first voltage-dividing resistor is R1, the resistance of the second voltage-dividing resistor is R2, the operating voltage of the main control chip and the DRAM chip is V1, and the USB power supply voltage is V0, then R1, R2, V1 and V0 satisfy the following relationship: R2 / (R1+R2)=V1 / V0;

[0021] The switch diode is located between the anode of the USB interface power line and the first active end of the single-pole double-throw switch, and is used to prevent the super capacitor from discharging in the path of the two voltage-dividing resistors;

[0022] The connection end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the wake-up pin of the main control chip, and the connection end of the first voltage-dividing resistor and the USB interface is connected to the anode of the switching diode;

[0023] When the single-pole double-throw switch is closed at the first active end and the security USB flash drive is connected to the host, the voltage on the wake-up pin jumps to a high level, thereby waking up the main control chip; when the single-pole double-throw switch is closed at the first active end and the security USB flash drive is disconnected from the host, the voltage on the wake-up pin jumps to a low level, thereby putting the main control chip into sleep mode.

[0024] Beneficial effects: The present invention allows the main control chip to sleep in order to save power consumption; the switching diode is used to prevent the super capacitor from discharging in the path of the two voltage-dividing resistors, which is also to save power consumption. The reduction in power consumption indirectly increases the upper limit of the data survival time and improves the practicality of the system.

[0025] Preferably, the single-pole double-throw switch is connected to a shift block located on the surface of the USB flash drive housing, and is used to switch the single-pole double-throw switch to the first active end or the second active end by sliding the shift block.

[0026] Beneficial effect: The present invention connects the single-pole double-throw switch to the dial block on the surface of the shell, so that the user can directly realize offline data erasure through the mechanical structure.

[0027] Preferably, the interior of the secure USB flash drive also includes: an extension dial block parallel to the USB interface, one end of the extension dial block is connected to the dial block of the single-pole double-throw switch, and the other end extends a certain length from the interior of the secure USB flash drive when the single-pole double-throw switch is closed at the first active end, and is completely hidden inside the secure USB flash drive when the single-pole double-throw switch is closed at the second active end.

[0028] Beneficial effect: The present invention uses a secure USB flash drive with an extended dial block and a confidential host with a USB interface of a specific structure. When the secure USB flash drive is disconnected from the confidential host, the dial block is pushed in, causing the single-pole double-throw switch to close to the second active end, thereby erasing the data in the DRAM chip.

[0029] Preferably, when the operating voltages of the main control chip and the DRAM chip are inconsistent, two linear voltage regulator chips are used to provide corresponding power supplies for the main control chip and the DRAM chip respectively.

[0030] Preferably, the secure USB flash drive uses multiple DRAM chips of the same model to expand the capacity of the secure USB flash drive.

[0031] In order to achieve the above-mentioned object, according to a second aspect of the present invention, a data security migration system is provided, the security migration system comprising: a common host computer, a confidential host computer and a DRAM-based secure USB flash drive;

[0032] When the DRAM-based secure USB flash drive is a secure USB flash drive as described in the first six aspects of the first aspect, secure data migration is achieved in the following manner:

[0033] Define "data on a common host computer is migrated to another common host computer via a secure USB flash drive" as usage mode 1, define "data on a common host computer is migrated to a confidential host computer via a secure USB flash drive" as usage mode 2, define "data on a confidential host computer is migrated to another confidential host computer via a secure USB flash drive" as usage mode 3, and define "data on a confidential host computer is migrated to a common host computer via a secure USB flash drive" as usage mode 4;

[0034] If any of the following conditions are used:

[0035] When the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as the power supply, the source host computer will charge the super capacitor inside the secure USB flash drive;

[0036] When the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain data until it is connected to the destination host computer to complete data migration;

[0037] When the DRAM-based secure USB flash drive is a secure USB flash drive as described in the last three aspects of the first aspect, secure data migration is achieved in the following manner:

[0038] Under the condition of usage mode 1, when the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as the power supply, the source host computer will charge the super capacitor inside the secure USB flash drive; when the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain data until it is connected to the destination host computer to complete data migration;

[0039] Under the condition of usage mode 2, when the secure USB flash drive is inserted into the confidential host computer, the protrusion of the same length at the corresponding position of the USB female connector on the confidential host computer will switch the single-pole double-throw switch to the second active end through the extension block. When the secure USB flash drive is disconnected from the confidential host computer, the data in the DRAM chip will be automatically erased;

[0040] Under the conditions of usage mode 3 or usage mode 4, the data in the DRAM chip is automatically erased the moment the secure USB flash drive is disconnected from the source host computer.

[0041] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0042] (1) The present invention uses DRAM volatile storage medium as the U disk storage medium. Once the DRAM chip is taken out by violent cracking, all internal data will be lost in a short time due to the loss of power supply, which can prevent the chip data from being read by violent disassembly, thereby enhancing the data anti-theft capability. Compared with ordinary CD-ROM discs that can only be written once, common Flash storage systems have certain limitations on the number of erasures and writes. DRAM technology is designed for fast and repeated erasures, and the number of storage medium erasures and writes is unlimited. Therefore, compared with traditional storage media, it also has a natural huge advantage in the number of erasures and writes, which saves resources to a great extent.

[0043] (2) The present invention adds a time limit for data usage and provides two methods of software-controlled data erasure and hardware-level data erasure to implement data usage restrictions, which is beneficial to reducing the risk of data leakage and enhancing data management security.

[0044] (3) The present invention realizes a self-powered circuit through a supercapacitor and a linear voltage regulator chip. The self-powered circuit cooperates with a DRAM storage medium. When the secure USB flash drive is not connected to a host computer and the single-pole double-throw switch is closed at the second active end, the supercapacitor is short-circuited and discharged. After the DRAM chip loses power, its internal data is completely erased and cannot be restored. This realizes offline and reliable destruction of the internal data of the USB flash drive without relying on a host computer, thereby preventing data leakage. Compared with the software erasing method of non-volatile storage chips such as Flash, this method of erasing data is irreversible, thereby fundamentally ensuring the security of data erasure.

[0045] (4) The present invention proposes a data security migration system. Through the joint design of the secure U disk and the confidential host computer interface, an extension block is added to the single-pole double-throw switch block of the secure U disk, which cooperates with the extension protrusion at the USB female head of the confidential host computer. After the secure U disk is connected to the confidential host computer, the single-pole double-throw switch is forced to be pushed to the second active end, and the stored electricity in the internal power supply circuit is quickly released. Once the secure U disk and the confidential host computer are disconnected after completing data exchange, the DRAM chip loses power and the internal data is automatically erased. Compared with the existing solution, the hardware device can effectively prevent the illegal removal of data from the confidential host computer, which is in line with the data security management specifications of the confidential environment and reduces the risk of data leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of the structure of a secure USB flash drive based on DRAM provided by the present invention;

[0047] FIG2( a ) is a schematic diagram of the extended shift block provided by the present invention in an extended state;

[0048] FIG2( b ) is a schematic diagram of the extended dial block provided by the present invention in a hidden state;

[0049] Figure 3 A schematic diagram of a functional topology structure of a secure USB flash drive based on DRAM provided by the present invention;

[0050] Figure 4 A schematic diagram of a data transmission module provided by the present invention;

[0051] Figure 5 A schematic diagram of an encryption storage module provided by the present invention;

[0052] Figure 6 A schematic diagram of a mobile power supply module provided by the present invention;

[0053] Figure 7 A schematic diagram of a voltage adapter module provided by the present invention;

[0054] Figure 8 A schematic diagram of a device discharge module provided by the present invention;

[0055] Fig. 9 A schematic diagram of the interface of the confidential upper computer provided by the present invention;

[0056] Fig.10 Four working state transition diagrams of the DRAM-based secure USB flash drive provided by the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0058] like Figure 1 As shown, the present invention provides a secure USB flash drive based on DRAM, the secure USB flash drive comprising: a USB interface J1, a self-powered circuit, a main control chip IC1 and a DRAM chip IC2;

[0059] The power line anode of the USB interface is connected to the self-powered circuit, and the signal line is connected to the main control chip, so as to realize the connection between the secure U disk and the host computer;

[0060] The self-powered circuit is used to convert the voltage provided by the host computer into the working voltage of the main control chip and the DRAM chip when the secure USB flash drive is connected to the host computer, and supply power to the main control chip and the DRAM chip; when the secure USB flash drive is not connected to the host computer, the self-powered circuit supplies power to the main control chip and the DRAM chip by itself;

[0061] The main control chip is connected to the DRAM chip. When the host computer sends data to be written to the secure U disk, it first sends a write data request to the main control chip through the USB signal line, and then sends the data to be written to the main control chip. The main control chip encrypts the data to be written and sends it to the DRAM chip for storage; when the host computer reads data from the secure U disk, the host computer sends a read data request to the main control chip, and the main control chip forwards the request to the DRAM chip to read the data. The DRAM chip sends the ciphertext of the requested data to the main control chip. After receiving the requested data, the main chip decrypts it and sends the decrypted plaintext data to the host computer through the USB signal line.

[0062] The present invention uses DRAM instead of Flash chip as the U disk storage medium. Once the DRAM chip is disassembled and taken out, all internal data will be lost in a very short time due to power loss, thereby resisting brute force cracking. In addition, the DRAM storage medium has unlimited erasure times, which has a natural huge advantage over traditional storage media in terms of erasure times, and can save resources to a great extent. The "host computer" here can be an ordinary host computer or a confidential host computer.

[0063] Preferably, when the secure U disk is disconnected from the host computer, the self-powered circuit continuously outputs the operating voltage of the main control chip and the DRAM chip to supply power to the main control chip and the DRAM chip; the timing starts from 0 from the moment the secure U disk is disconnected from the host computer. If the statistical time of the secure U disk disconnection exceeds the set threshold, the main control chip cuts off the clock supply and self-refresh command to the DRAM chip. After the DRAM loses the clock and stops self-refreshing, the data will be lost.

[0064] The present invention introduces software timing means to limit the survival time of internal data in the USB flash drive when it is in a mobile state from the software level. When the USB flash drive is disconnected from the host computer, the data in the DRAM is erased after a certain time limit. This data usage restriction is conducive to reducing the risk of data leakage and strengthening data security management.

[0065] Preferably, the self-powered circuit comprises: a single-pole double-throw switch S1, a super capacitor C1 and a linear voltage regulator chip IC3;

[0066] The common end of the single-pole double-throw switch is connected to the anode of the supercapacitor, the first active end is connected to the USB interface, and the second active end is grounded; the anode of the supercapacitor is connected to the common end of the single-pole double-throw switch, and the cathode is grounded; when the secure U disk is connected to the host computer and the single-pole double-throw switch is switched to the first active end, the host computer charges the supercapacitor; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is switched to the first active end, the supercapacitor supplies power to the main control chip and the DRAM chip; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is switched to the second active end, the supercapacitor is short-circuited and discharged, the DRAM chip loses power supply, and the internal data is completely erased.

[0067] The input end of the linear voltage regulator chip is connected to the first active end of the single-pole double-throw switch, and the output end is connected to the main control chip and the DRAM chip. When the input voltage is greater than or equal to the minimum operating voltage of the linear voltage regulator chip, the input voltage is stepped down and converted into the operating voltage of the main control chip and the DRAM chip; when the input voltage is less than the minimum operating voltage of the linear voltage regulator chip, power supply is provided at a voltage lower than the operating voltage of the main control chip and the DRAM chip.

[0068] The present invention realizes a self-powered circuit through a supercapacitor and a linear voltage regulator chip. The self-powered circuit cooperates with a DRAM storage medium. When the host computer is not connected and the second active end is thrown, the supercapacitor is short-circuited and discharged. After the DRAM chip loses power, it can ensure that its internal data is completely erased and cannot be restored. Under the premise of not relying on the host computer, the internal data can be destroyed offline reliably to prevent data leakage. This data erasure solution is far superior to the data destruction solution of the optical disk shredder.

[0069] Preferably, when the U disk is not connected to the host computer, when the voltage provided by the self-powered circuit is the working voltage of the main control chip and the DRAM chip, the data inside the mobile secure U disk can be maintained; when the provided voltage is lower than the working voltage of the main control chip and the DRAM chip, the data inside the mobile secure U disk is lost.

[0070] The present invention introduces supercapacitors and linear voltage regulator chips to limit the survival time of internal data in the USB flash drive in a mobile state from a hardware level. When the output voltage is lower than the working voltage, the main control chip and the DRAM chip lose power, and the data in the USB flash drive will also be lost. Adding time limits to the use of data is conducive to strengthening data security management and reducing the risk of data leakage.

[0071] The hardware-level data survival time limit of the USB flash drive is determined by the circuit design and component parameters. When calculating the maximum power supply time of the USB flash drive using the supercapacitor power supply module when it is mobile, that is, when calculating the maximum data survival time, the data that needs to be involved in the calculation include: the initial potential of the supercapacitor built into the mobile power supply module when it is removed Supercapacitor minimum effective supply voltage (In this embodiment, it is the minimum input voltage for the normal operation of the voltage regulator chip), the nominal value of the super capacitor C and the system sleep current I in the mobile state. In this way, the present invention can easily obtain an upper limit of the data survival time Under ideal working conditions, the upper limit of this time is the maximum power supply time.

[0072] The USB protocol stipulates that it is 5V and cannot be changed by the user. Therefore, in order to adjust the maximum power supply time T of the system, there are the following options:

[0073] 1) Reduce I to increase T through selection adjustment or software optimization;

[0074] 2) Increase T by increasing the nominal value C of the supercapacitor;

[0075] 3) Reduce the minimum input voltage value of the voltage regulator chip by selecting To increase T.

[0076] In addition, the present invention can also improve the power supply mode by changing To increase T, this includes:

[0077] Fine-tuning circuit solution 1: Connect a boost circuit between the 5V power line and the capacitor anode to directly increase

[0078] Fine-tuning circuit solution 2: Connect a battery before the voltage input terminal of the voltage regulator chip, set the voltage to V0, connect the positive pole of the battery to the input terminal of the voltage regulator chip, and connect the negative pole to the part that should be connected to the power input terminal of the voltage regulator chip. Thus, the input voltage of the voltage regulator chip becomes the anode potential of the capacitor. The sum of V0 and V1. Then the calculation formula of data survival time T becomes: The increase in T value is CV0 / I.

[0079] Preferably, if Figure 1 As shown, the self-powered circuit further includes: a first voltage-dividing resistor R1, a second voltage-dividing resistor R2 and a switching diode D1;

[0080] The first voltage-dividing resistor and the second voltage-dividing resistor are connected in series between the USB interface and the ground, and are used to convert the voltage level on the USB power line into a voltage level compatible with the working voltage of the main control chip (in this embodiment, 5.0V is converted into 3.3V);

[0081] The switch diode is located between the USB interface and the first active end of the single-pole double-throw switch, and is used to prevent the super capacitor from discharging in the path of the two voltage-dividing resistors;

[0082] The connection end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the wake-up pin of the main control chip, and the connection end of the first voltage-dividing resistor and the USB interface is connected to the anode of the switching diode;

[0083] When the single-pole double-throw switch is switched to the first active end and the secure USB flash drive is connected to the host, the voltage on the wake-up pin jumps to a high level, thereby waking up the main control chip; when the single-pole double-throw switch is switched to the first active end and the secure USB flash drive is disconnected from the host, the voltage on the wake-up pin jumps to a low level, thereby putting the main control chip into sleep mode.

[0084] The present invention saves power consumption by waking up and sleeping the main control chip.

[0085] Preferably, the single-pole double-throw switch is connected to a shift block located on the surface of the USB flash drive housing, and is used to switch the connection between the first active end (end a) and the second active end (end b) of the single-pole double-throw switch by sliding the shift block.

[0086] The present invention connects a single-pole double-throw switch to a dial block on the surface of a housing, so that a user can realize a one-touch offline data erasing function through a mechanical structure.

[0087] Preferably, the secure USB flash drive also includes: an extension block parallel to the USB interface, one end of the extension block is connected to the block, as shown in Figure 2 (a), and the other end extends from the inside of the USB flash drive to a certain length when the single-pole double-throw switch is turned to the first active end, as shown in Figure 2 (b), and is completely hidden inside the USB flash drive when the single-pole double-throw switch is turned to the second active end. Its functional characteristics are described later in the Fig. 9 Introduction.

[0088] Preferably, the length of the extended dial block is greater than or equal to the length leaked after the USB interface is normally connected to the host computer.

[0089] Preferably, when the operating voltages of the main control chip and the DRAM chip are inconsistent, two voltage stabilizing chips are used to provide operating voltages for the main control chip and the DRAM chip respectively.

[0090] Preferably, the secure USB flash drive uses multiple identical DRAM chips to expand the capacity of the secure USB flash drive.

[0091] Overall, Figure 1 The specific connection method of the circuit described in is described as follows: the USB interface J1 leads out two pairs of lines, among which the differential signal line is connected to the high-performance main control chip IC1; the anode of the power line of J1 is connected to the anode of the diode, and is also connected to one end of the voltage-dividing resistor R1, and the cathode is grounded; the other end of the voltage-dividing resistor R1 is connected to the high-performance main control chip, providing a wake-up signal line B4, and is also connected to one end of the voltage-dividing resistor R2; the other end of the voltage-dividing resistor R2 is grounded; the cathode of the diode D1 is connected to the power input end of the linear voltage regulator chip IC3, and is also connected to an active end a of the single-pole double-throw switch; the fixed end of the single-pole double-throw switch S1 is connected to the anode of the supercapacitor, and its other active end b is grounded; the cathode of the supercapacitor C1 is grounded; the output end of the linear voltage regulator chip IC3 is connected to both the power port of the high-performance main control chip IC1 and the power port of the DRAM chip IC2; the high-performance main control chip IC1 leads out the address bus B1, the parallel data bus B2 and the control bus B3 respectively, and is connected to the corresponding ports of the instructing DRAM chip IC2 respectively.

[0092] The software part is inside the main control chip IC1, and consists of three parts: USB communication part, encryption storage part and sleep wake-up part. Among them, the USB module is responsible for controlling the data interaction between the main control chip IC1 and the USB interface J1 (this interface is used to connect to the host computer); the encryption storage part is responsible for encrypting the data written into the storage medium and decrypting the data read out of the storage medium, and is also responsible for driving the DRAM chip IC2 using the address bus B1, parallel data bus B2 and control bus B3; the sleep wake-up part regulates the sleep and wake-up of the system according to the level of the sleep wake-up signal line B4. When B4 is high, the system runs at normal power consumption, and when B4 is low, the system enters sleep.

[0093] like Figure 3 As shown, the DRAM-based secure USB flash drive proposed in the present invention is divided into the following functional aspects: a data transmission module consisting of a high-performance main control chip supporting encryption function and a USB data bus; an encryption storage module consisting of a DRAM chip (dynamic random read-write memory chip, a type of volatile storage) and a related bus; a mobile power supply module designed to limit the data survival time when the USB flash drive is mobile and consisting of a diode, a resistor, and a super capacitor in a specific circuit structure; a voltage adaptation module realized by a combination of a linear voltage regulator chip, a voltage divider resistor, and an auxiliary circuit; and a device discharge module consisting of a USB interface designed in a specific structure, a toggle switch, and a circuit for discharging the super capacitor inside the mobile power supply module.

[0094] The working principles of different modules are described below.

[0095] like Figure 4 As shown in the figure, the data transmission module is mainly composed of ①USB controller part of the high-performance main control chip, a pair of ②USB data differential buses and ③physical interface. After the secure USB flash drive is connected to the host computer, the USB flash drive device uses the USB controller inside the high-performance main control chip to communicate with the host computer through the USB data differential bus, perform USB enumeration response, media formatting, file system establishment, file reading and writing, and other operations, and establish a complete large-capacity storage communication process. From the beginning of the data entering the USB differential bus from the host computer interface to being parsed by the USB controller of the main control chip, it exists in plain text; it becomes an encrypted data stream only when the data enters the data encryption component.

[0096] like Figure 5As shown in the figure, the encrypted storage module consists of ① DRAM chip, ② DRAM driver component and ③ data encryption component on the main control chip, ④ address bus between DRAM chip and main control chip, ⑤ parallel data bus, and ⑥ control bus. The control bus and address bus signals jointly determine the commands executed by the DRAM chip, such as DRAM initialization or data reading and writing; the parallel data bus is responsible for transmitting data signals and carrying read and write data streams, which is the basic principle of the lowest-level DRAM driver. With the support of the DRAM driver component, the system establishes a file system in the DRAM storage chip to realize file storage and reading and writing. The main control chip uses the internal data encryption component to decrypt and encrypt data during the file data reading and writing operations of the DRAM chip, thereby ensuring that the file data inside the DRAM chip is always encrypted to protect data security.

[0097] like Figure 6 As shown in the figure, the mobile power supply module is specifically composed of ① USB power line, ② super capacitor, ③ diode, ④ system wake-up line and other wires. Among them, the positive pole of the USB power line is pulled down to the ground, and the negative pole is directly connected to the ground, so the positive pole of the USB power line is at a high level when the secure USB flash drive is connected to the host computer, and at a low level when it is removed. Therefore, the conversion of the access state of the secure USB flash drive can be converted into a level change of the positive pole of the USB power line, and a wake-up signal is provided to the main control chip through the system wake-up line to control the sleep and wake-up of the entire system. In addition, the positive pole of the USB power line is connected to the super capacitor and the voltage adapter module in the forward direction through the diode to power them respectively. Therefore, when the secure USB flash drive is connected to the host computer, the mobile power supply module uses the positive pole of the USB power line to power the voltage adapter module on the one hand, and charges the capacitor through the turned-on diode on the other hand, and outputs a high level on the system wake-up line; after the secure USB flash drive is disconnected from the host computer, due to the reverse cutoff characteristics of the diode, the supercapacitor and the positive pole of the USB power line are disconnected, and the mobile power supply module supplies power from the supercapacitor output to the voltage adapter module, while the USB power line and the system wake-up line are both at a low level.

[0098] like Figure 7 As shown, the voltage adapter module consists of ① a voltage regulator chip and ② a voltage divider resistor. The main interfaces of the voltage regulator chip are the input voltage terminal and the output voltage terminal, and the other interfaces include the ground terminal, the enable terminal and the voltage regulator capacitor terminal. The function of the voltage regulator chip is to step down a certain range of input voltage and convert it into a certain voltage to be output from the output voltage terminal. It can provide a large output current and is suitable for power supply. The voltage divider resistor can also realize voltage conversion, but its output is not suitable for power supply, and is only suitable for providing a level signal of a specified voltage. The input ends of the voltage regulator chip and the voltage divider resistor are connected to the supercapacitor output end of the mobile power supply module, and the output end is connected according to the needs of the other modules.

[0099] like Figure 8 As shown, the device discharge module is composed of ① a single-pole double-throw toggle switch and ② a capacitor discharge circuit. The role of the selected single-pole double-throw switch in the present invention is to switch the access state of the supercapacitor. Here, the supercapacitor refers to the supercapacitor inside the mobile power supply module, and the rest of this paragraph will not be repeated. The single-pole double-throw toggle switch has a fixed end and two active ends, and has two connection states. In both states, the switch connects the fixed end to one of the active ends and disconnects the connection to the other active end. In the design of the present invention, the cathode end of the supercapacitor is connected to the ground wire, and the anode end is connected to the fixed end of the toggle switch. The switch is placed at the second active end so that the fixed end of the switch is directly grounded, so that both ends of the supercapacitor are grounded at the same time and the charge is released; the switch is placed at the first active end so that the fixed end of the switch is connected to the cathode of the diode, so that the supercapacitor can be charged by the power supply of the USB interface. Thus, by adjusting the toggle switch under mobile conditions, the function of "manual offline data erasure" can be realized.

[0100] Preferably, in this embodiment, the USBA class interface female head of the host computer in the confidential environment and the USBA class interface male head of the present invention both adopt a special structural design (specific reference design schematic diagrams are shown in Figures 2(a), 2(b) and Fig. 9 ), in conjunction with a single-pole double-throw switch, to achieve the following purpose: the data is automatically erased when the secure USB flash drive is disconnected from the secure host computer.

[0101] As shown in Figure 2(a) and Figure 2(b), in this embodiment, an extended shift block is additionally connected to the shift block position of the single-pole double-throw switch. The shift block and the extended shift block are integrated and can slide left and right at the same time. The extended shift block extends an additional section at the USB interface to the deepest insertion position of the host computer female connector. When the shift block of the single-pole double-throw switch is on the left, it corresponds to being placed at the first active end, and the supercapacitor C1 inside the mobile power supply module M3 is in a power storage state; when the shift block is on the right, it corresponds to being placed at the second active end, and C1 is in a discharge state. Fig. 9 As shown, in this embodiment, in the female part of the USBA class interface on the confidential host computer side, a section corresponding to the position of the extended dial switch of the male head of the secure USB flash drive is also extended, and the extended length is the same as the active distance of the dial switch.

[0102] After adopting the above structure, the working process of the device's "automatically erase data after disconnecting from the confidential host computer" function is as follows:

[0103] The working scenario targeted by this part of the structure is that the secure U disk carries data and migrates it to the host computer in a confidential environment. Before the secure U disk carrying data is connected to the host computer in the confidential environment, the supercapacitor inside its mobile power supply module contains stored electricity. After the secure U disk device is connected, the extended part of the USB interface female head presses against the extended slider of the secure U disk device and pushes it from the first active end to the second active end, and during the entire process of data interaction with the host computer in the confidential environment, the single-pole double-throw switch slider is locked at the second active end. The effect is that from the moment the secure U disk is connected, the two ends of the capacitor of the internal mobile power supply module begin to short-circuit. Because the resistance is very small during short-circuiting, the supercapacitor quickly completes discharge and the mobile power supply module loses its power supply capacity.

[0104] When the secure USB flash drive completes data interaction with the host computer in the confidential environment and is unplugged, the entire secure USB flash drive loses all power, and the DRAM data is lost and cannot be recovered. This implements the "automatic data erasure upon unplugging" function to prevent malicious users from copying files out of the confidential environment.

[0105] When the secure USB flash drive is used in a common host computer, since the host computer does not have a special protruding structure, the present invention can be used as a normal USB flash drive as long as the toggle switch is placed at the first active end.

[0106] The present invention provides a data security migration system, the security migration system comprising: a common host computer, a confidential host computer and a DRAM-based security USB flash drive;

[0107] When the DRAM-based secure USB flash drive is one of the first six types, if the data on an ordinary host computer is migrated to another ordinary host computer through the secure USB flash drive, or, the data on an ordinary host computer is migrated to a confidential host computer through the secure USB flash drive, or, the data on a confidential host computer is migrated to another confidential host computer through the secure USB flash drive, or, the data on a confidential host computer is migrated to an ordinary host computer through the secure USB flash drive, when the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as a power supply, the source host computer will charge the super capacitor inside the secure USB flash drive; when the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain the data until it is connected to the destination host computer to complete the data migration. However, the last situation does not meet the specifications for confidential data management and usually does not occur.

[0108] When the DRAM-based secure USB flash drive is one of the following three types,

[0109] If the data on an ordinary host computer is migrated to another ordinary host computer via a secure USB flash drive, when the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as a power supply, the source host computer will charge the super capacitor inside the secure USB flash drive; when the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain the data until it is connected to the destination host computer to complete the data migration;

[0110] If the data on the ordinary host computer is migrated to Fig. 9 When the secure USB flash drive is inserted into the confidential host computer, the protrusion at the corresponding position of the USB female connector on the confidential host computer will switch the single-pole double-throw switch to the second active end through the extended dial block. When the secure USB flash drive is disconnected from the confidential host computer, the data in the DRAM chip will be automatically erased.

[0111] If the data on a confidential host computer is migrated to another confidential host computer or a common host computer via a secure USB flash drive, the data in the DRAM chip is automatically erased the moment the secure USB flash drive is disconnected from the source host computer. Therefore, the data cannot be migrated to the destination host computer. This migration is blocked by the device, thus preventing the data from being transferred out of the confidential host computer, and ensuring the security of data migration in a confidential environment.

[0112] In the application scenario of the present invention, usage mode 2 is the main application mode, and usage mode 4 is an application mode that does not comply with the confidential data management policy.

[0113] like Fig.10 As shown, the present invention abstracts four device working states: mobile no data state, wired no data state, mobile data retention state and wired data retention state. The transfer process between the four working states is as follows: in the mobile no data state, if the secure U disk is connected to the host computer, it will enter the wired no data state; in the wired no data state, if the secure U disk is disconnected from the host computer, it will enter the mobile no data state; if the secure U disk is authenticated and data is read and written, it will enter the wired data retention state; in the wired data retention state, if the secure U disk is disconnected from the host computer, it will enter the mobile data retention state; if the secure U disk is erased by software-controlled data, it will enter the wired no data state; in the mobile data retention state, if the secure U disk is connected to an unauthenticated host computer, it will enter the wired data retention state; if the secure U disk is connected to an unauthenticated host computer, it will enter the wired no data state; if the secure U disk experiences a data survival timeout, or the user switches to erase data with one key, or is violently disassembled, it will enter the mobile no data state.

[0114] Taking the module as the basic unit, the workflow of the secure USB flash drive in a normal confidential data migration scenario is as follows:

[0115] A working cycle of the device starts with the device being connected to the host computer. The host computer first supplies power to the voltage adapter module and the mobile power supply module through the USB interface. The mobile power supply module is in a charging state after being connected to the host computer, and will be fully charged in a very short time, while the voltage adapter module converts the power supply voltage provided by the USB interface into the working voltage required by other modules and outputs it accordingly. After obtaining power supply, the data transmission module and the encryption storage module are first initialized, and then the data transmission module establishes USB communication with the host computer through the USB interface, becoming a bridge between the host computer and the encryption storage module. The host computer then takes the lead in establishing, mounting and reading and writing files in the encryption storage module for the encrypted file system. After completing file reading and writing, the device of the present invention will be unplugged. At this time, the USB interface of the device is disconnected, the USB power line loses power supply, and the mobile power supply module can detect such a state transition. On the one hand, its internal super capacitor enters the discharge mode, replaces the USB power supply to continue to provide power to the voltage conversion module, and on the other hand, the state transition signal is conveyed to the data transmission module and the encryption storage module through the main control wake-up line. The data transmission module and the encryption storage module enter a dormant state, and the main energy consumption is used for data retention of the DRAM chip in the encryption storage module. In this process, the power of the mobile power supply module is gradually consumed and the voltage drops. If the secure USB flash drive cannot be connected to an effective host device in time, the output of the mobile power supply module will decay until it disappears, and the data in the encrypted storage module will be completely lost due to power failure. If the device is connected to an effective host device in time, the mobile power supply module will first detect the state transition, and the supercapacitor will enter the charging mode. At the same time, the module sends a wake-up signal to the main control chip, leading the wake-up of the entire system, and the system enters a new round of work cycle.

[0116] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A secure USB flash drive based on DRAM, characterized in that: The secure USB flash drive includes: a USB interface, a self-powered circuit, a main control chip and a DRAM chip; The power line anode of the USB interface is connected to the self-powered circuit, the differential signal line of the USB interface is connected to the main control chip, and the USB interface is used to realize the connection between the secure U disk and the host computer; The self-powered circuit is used to convert the voltage provided by the host computer through the USB interface into the working voltage of the main control chip and the DRAM chip when the secure USB flash drive is connected to the host computer, and to supply power to the main control chip and the DRAM chip; when the secure USB flash drive is not connected to the host computer, the self-powered circuit supplies power to the main control chip and the DRAM chip by itself; The main control chip is connected to the DRAM chip, and is used for sending a write data request to the main control chip through the USB signal line when the host computer sends data to be written to the secure U disk, and then sending the data to be written to the main control chip, and the main control chip encrypts the data to be written and sends it to the DRAM chip for storage; when the host computer reads data from the secure U disk, the host computer sends a read data request to the main control chip, the main control chip requests to read data from the DRAM chip, the DRAM chip sends the ciphertext of the requested data to the main control chip, the main control chip decrypts the received ciphertext of the requested data into plaintext, and sends the plaintext to the host computer through the USB signal line; From the moment the secure USB flash drive is disconnected from the host computer, the statistical time starts from 0. If the statistical duration of the secure USB flash drive disconnection exceeds the set threshold, the main control chip cuts off the clock supply and self-refresh command to the DRAM chip. After the DRAM loses the clock and stops self-refreshing, the data is lost. During the period when the secure USB flash drive is not connected to the host computer, the self-power supply circuit continues to provide the main control chip and the DRAM chip with working voltage and power. Among them, the self-powered circuit includes: a single-pole double-throw switch, a supercapacitor and a linear voltage regulator chip; the common end of the single-pole double-throw switch is connected to the anode of the supercapacitor, the first active end is connected to the USB interface, and the second active end is grounded; the anode of the supercapacitor is connected to the common end of the single-pole double-throw switch, and the cathode is grounded; when the secure U disk is connected to the host computer and the single-pole double-throw switch is closed at the first active end, the host computer charges the supercapacitor; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is closed at the first active end, the supercapacitor supplies power to the main control chip and the DRAM chip; when the secure U disk is not connected to the host computer and the single-pole double-throw switch is closed at the second active end, the supercapacitor is short-circuited and discharged, the DRAM chip loses power supply, and the internal data is completely erased.

2. The secure USB flash drive according to claim 1, wherein: The input end of the linear voltage regulator chip is connected to the first active end of the single-pole double-throw switch, and the output end is connected to the main control chip and the DRAM chip. When the input voltage is greater than or equal to the minimum working voltage of the linear voltage regulator chip, the input voltage is stepped down and converted into the working voltage output of the main control chip and the DRAM chip; when the input voltage is less than the minimum working voltage of the linear voltage regulator chip, the working voltage supply of the main control chip and the DRAM chip is cut off.

3. The secure USB flash drive according to claim 2, wherein: By adjusting the minimum effective supply voltage of the supercapacitor At least one of the nominal value C of the supercapacitor and the system sleep current I in the mobile state is used to adjust the lifetime T of the data inside the secure USB flash drive. The above parameters satisfy the following relationship in, Indicates the initial potential of the supercapacitor built into the mobile power supply module when it is unplugged.

4. The secure USB flash drive according to claim 2 or 3, wherein: The self-powered circuit further includes: a first voltage-dividing resistor, a second voltage-dividing resistor and a switching diode; The first voltage-dividing resistor and the second voltage-dividing resistor are connected in series between the anode of the USB interface and the ground, and are used to convert the voltage level on the USB power line into a level compatible with the working voltage of the main control chip, wherein one end of the second voltage-dividing resistor is directly connected to the ground; Assume that the resistance of the first voltage-dividing resistor is R1, the resistance of the second voltage-dividing resistor is R2, the operating voltage of the main control chip and the DRAM chip is V1, and the USB power supply voltage is V0, then R1, R2, V1 and V0 satisfy the following relationship: R2 / (R1+R2)=V1 / V0; The switch diode is located between the anode of the USB interface power line and the first active end of the single-pole double-throw switch, and is used to prevent the super capacitor from discharging in the path of the two voltage-dividing resistors; The connection end of the first voltage-dividing resistor and the second voltage-dividing resistor is connected to the wake-up pin of the main control chip, and the connection end of the first voltage-dividing resistor and the USB interface is connected to the anode of the switching diode; When the single-pole double-throw switch is closed at the first active end and the security USB flash drive is connected to the host, the voltage on the wake-up pin jumps to a high level, thereby waking up the main control chip; when the single-pole double-throw switch is closed at the first active end and the security USB flash drive is disconnected from the host, the voltage on the wake-up pin jumps to a low level, thereby putting the main control chip into sleep mode.

5. The secure USB flash drive according to claim 4, wherein: The single-pole double-throw switch is connected to a shift block located on the surface of the USB flash drive housing, and is used to switch the single-pole double-throw switch to the first active end or the second active end by sliding the shift block.

6. The secure USB flash drive according to claim 5, wherein: The interior of the secure USB flash drive also includes: an extension dial block parallel to the USB interface, one end of the extension dial block is connected to the dial block of the single-pole double-throw switch, and the other end extends a certain length from the interior of the secure USB flash drive when the single-pole double-throw switch is closed at the first active end, and is completely hidden inside the secure USB flash drive when the single-pole double-throw switch is closed at the second active end.

7. The secure USB flash drive according to claim 6, wherein: When the operating voltages of the main control chip and the DRAM chip are inconsistent, two linear voltage regulator chips are used to provide corresponding power supplies for the main control chip and the DRAM chip respectively.

8. The secure USB flash drive according to claim 7, wherein: The secure USB flash drive uses multiple DRAM chips of the same model to expand the capacity of the secure USB flash drive.

9. A data security migration system, characterized in that: The secure migration system includes: a common host computer, a confidential host computer and a secure USB disk based on DRAM; When the DRAM-based secure USB flash drive is a secure USB flash drive as described in any one of claims 1 to 5, secure data migration is achieved in the following manner: Define "data on a common host computer is migrated to another common host computer via a secure USB flash drive" as usage method 1, define "data on a common host computer is migrated to a confidential host computer via a secure USB flash drive" as usage method 2, define "data on a confidential host computer is migrated to another confidential host computer via a secure USB flash drive" as usage method 3, and define "data on a confidential host computer is migrated to a common host computer via a secure USB flash drive" as usage method 4; If any of the following conditions are used: When the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as the power supply, the source host computer will charge the super capacitor inside the secure USB flash drive; When the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain data until it is connected to the destination host computer to complete data migration; When the DRAM-based secure USB flash drive is a secure USB flash drive as described in any one of claims 6 to 8, secure data migration is achieved in the following manner: Under the condition of usage mode 1, when the secure USB flash drive is inserted into the source host, if the secure USB flash drive uses a super capacitor as the power supply, the source host computer will charge the super capacitor inside the secure USB flash drive; when the secure USB flash drive is disconnected from the source host computer, the secure USB flash drive uses a self-powered circuit to retain data until it is connected to the destination host computer to complete data migration; Under the condition of usage mode 2, when the secure USB flash drive is inserted into the confidential host computer, the protrusion of the same length at the corresponding position of the USB female connector on the confidential host computer will switch the single-pole double-throw switch to the second active end through the extension block. When the secure USB flash drive is disconnected from the confidential host computer, the data in the DRAM chip will be automatically erased; Under the conditions of usage mode 3 or usage mode 4, the data in the DRAM chip is automatically erased the moment the secure USB flash drive is disconnected from the source host computer.

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