CN101630292B - File encryption-decryption method of USB removable storage device - Google Patents
File encryption-decryption method of USB removable storage device Download PDFInfo
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- CN101630292B CN101630292B CN2009101830691A CN200910183069A CN101630292B CN 101630292 B CN101630292 B CN 101630292B CN 2009101830691 A CN2009101830691 A CN 2009101830691A CN 200910183069 A CN200910183069 A CN 200910183069A CN 101630292 B CN101630292 B CN 101630292B
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Abstract
The invention relates to a file encryption-decryption method of a USB removable storage device, which is characterized in that two USB interfaces are respectively connected to a computer and a USB storage device, and a file data cluster of a FAT file system is identified by analyzing and filtering USB data stream of one of the USB interfaces; recentaly read and written data are stored temporarily in such a way that a buffer memory is set up and is mapped with an address of the USB storage device by a direct mapping method; then the identified file data are processed by encryption-decryption algorithm, replace data before, and finally are sent from another USB interface after returning to a physical layer; and a key can be obtained from a key generation module via a preset port.
Description
Technical field
The invention belongs to field of information security technology, particularly relate to a kind of method novel, that can carry out the file-level encryption and decryption to the data that deposit or read USB movable memory equipments such as USB flash disk in.
Background technology
Usually do not have under the network environment situation, under the isolated situation of physics between the network or under the big situation of transfer files, carry out easily data transmission and have to by means of the USB movable storage device.Seen in the market USB movable storage device scarcely has any security function, the file data of computing machine directly pass through USB port with expressly stored in form in the medium of USB movable storage device.In a lot of occasions, people do not recognize and are stored in safety of data in the USB movable storage device, and unique what can accomplish is exactly to guarantee that as far as possible USB flash disk can not lose.And generally speaking, the data of storing in the USB movable storage device after losing just cover all at one glance in his human eye.Simultaneously the USB movable storage device is borrowed mutually, is copied also and can bring the chance of stealing data to the assailant mutually, and along with improving constantly of the message transmission rate of USB, data moment of last G byte just can stealthily copy away by victim.
Existing safety approach has comprised and has improved security performance, data encryption equipment independently on safety practice on computers, the USB movable storage device.
Safety practice on first kind of computing machine is that the data that realize writing on the disk through the security control that in operating system nucleus, embeds USB interface unloading data are the ciphertext form, when needs are done corresponding decryption work during sense data from disk.This security mechanism is equivalent to add a ciphering and deciphering device at the disk leading portion, can guarantee the circulation of data within the specific limits, highly versatile.If use the mode of hardware circuit to realize that encryption and decryption is also less to the influence on the file reading speed.But this scheme need be made an amendment the kernel of operating system; Or the structure of mainboard made amendment, workload is big, standard can not get unified, in case arrived in the big scope; Just can't carry out sharing of file between the computing machine of various operating systems, produce meaningless trouble.And the maximum Windows operating system of present domestic use remains the operating system of a commercial operation; Domestic consumer can't make amendment to its kernel; Use this kind scheme can only be confined under the operating system of several kinds of openings of Linux, so be not widely used so far to the user of data protection.And big to make amendment expense height, difficulty of mainboard, be difficult to become the first-selection of domestic consumer and little company.
So in this case, the user who much thirsts for data security has thrown into sight on some encryption softwares, uses the way of compromising to satisfy the demand of oneself.Through authorizing the program on the PC, it is operated on the system layer, the data of the USB movable storage device of coming in and going out are carried out the security performance that encryption and decryption improves the USB movable storage device.This cipher mode has a lot of different forms, no matter be system self installed software or the application program that loads automatically through the autorun on the mobile device, has all used this mode.This cipher mode economic cost is low, need not to do change on the hardware.But the use of software is occupying system resources not only, but also receives the threat of wooden horse, virus easily.As a rule, this cipher mode needs manually input password, so the character of limited length, combination of numbers are easy to kidnapped by the wooden horse of running background.
Another kind of scheme from each big USB movable storage device manufacturing firm, their common ground is exactly that encrypting module is integrated on the movable storage device, makes himself to have function of keeping secret.But most of USB movable storage devices need the software support of extra operation on the computing machine.Because spreading unchecked of virus, this type software is not thought by mistake suspect object by the virus infringement by antivirus software and is isolated usually.Use and bring unnecessary trouble.These products change ciphering process by the hardware realization in addition, but the concrete encryption standard that uses is but openly fair, can't analyze its Expansion Theory, and security intensity is unknown.
Last a kind of encipherment scheme breaks away from computing machine and USB movable storage device fully, at first the data in the USB flash disk is all taken out during work, writes USB flash disk again after encrypting, then expressly deletion.There are several shortcomings in generally speaking such system, at first is not real-time encryption and decryption, uses the front and back of USB flash disk all must use this equipment to re-use after its encryption and decryption then at every turn; Secondly at every turn all totally data all come encryption and decryption one time, time-consuming and inconvenient.
Summary of the invention
Technical matters: the object of the invention is above-mentioned to the defective on the USB movable storage device data security protecting in order to overcome; A kind of file encryption-decryption method of USB movable storage device is proposed; Realize that disk file name and catalogue are visible and file content is invisible, more flexible in the use.The inventive method runs on the controller that is equipped with the USB principal and subordinate interface, powers on from opening, and respectively the USB principal and subordinate interface is realized the usb protocol stack of mass storage class, and is realized the exchange of data between principal and subordinate interface.
Technical scheme: the file encryption-decryption method of USB movable memory equipment of the present invention utilizes the characteristics of buffer memory fast access further to improve exchanges data speed between computing machine and the disk.The cipher mode of data can be decided according to the concrete configuration of hardware, and the cipher mode that can select hardware circuit to accomplish also can use software mode to realize.
The file encryption-decryption method of USB movable memory equipment of the present invention; Be connected to computing machine and USB memory device through master and slave USB interface; The usb data imported on any one USB interface stream is resolved, filtered, identify the file data bunch of FAT file system; Through opening up a block cache, adopt the method for directly mapping to shine upon mutually simultaneously, temporary reading recently and the data that write with the address of USB memory device; Then the file data that identifies is used enciphering and deciphering algorithm, and replace the data before the encryption and decryption, turn back to Physical layer at last again, send from another USB interface; Key obtains from key production module through the port of reserving.
Parsing, the filtration of described usb data stream are in same system, to be equipped with main a, driver from two USB interfaces and correspondence, and computing machine is disguised oneself as by common " USB memory device ", respond all computer requests; USB device to be encrypted disguises oneself as by " computing machine ", changes a little according to the computing machine sent request and is transmitted to the USB memory device once more; This process is divided into two stages, i.e. enumeration stage and data transfer phase; In enumeration stage; Microcontroller is through sending control request to the USB movable storage device; Device description, the configuration of obtaining this equipment described, interface is described, end points is described, character string is described and the largest logical unit number, the same request of using the foregoing description responsive computer that obtains from the USB movable storage device to initiate then; At data transfer phase; Microcontroller passes through the analysis to the data of transmitting with Bulk Only transmission mode; Utilize the cannonical format of CBW and SCSI, identify the order of main frame, the order beyond wherein Read10 and the Write10 is taked the means of complete transparent filtration memory device; Response to Read10: obtain the data that computing machine is asked from the USB movable memory equipment earlier, and then be transmitted to computing machine; Response to Write10: direct receiving computer data sent, and then store in the USB memory device.
The described file data that identifies the FAT file system bunch; It is characteristic according to write store or readout memory data; Judge that whether these data are file data bunch in the FAT file system; The possibility of getting rid of comprises: main record, DOS startup record, file allocation table 1, file allocation table 2, root directory data and the sub-directory data of starting, and preceding 5 can determine one's identity through the address of data; For the sub-directory data, because the regulation sub-directory must be with the file beginning of ". " and " .. " by name in the DOS file system, according to this characteristic and these two specific properties that the special directory item is had, its identity can be confirmed.
Be similar to the ICP/IP protocol layer, USB self also contains similar agreement, and lower floor is that the upper strata provides service, mutual communication between the logical layer, and real data stream all must be passed through physical channel.Fig. 4 describes is the relation between the usb protocol level of native system.The workflow of system is divided into two stages: enumeration stage and data transfer phase.In enumeration stage; Microcontroller is through sending control request to the USB movable storage device; Device description, the configuration of obtaining this equipment described, interface is described, end points is described, character string is described and the largest logical unit number, the same request of using the foregoing description responsive computer that obtains from the USB movable storage device to initiate then.At data transfer phase; Microcontroller passes through the analysis to the data of transmitting with Bulk Only transmission mode; Utilize the cannonical format of CBW and SCSI, identify the order of main frame, the order beyond wherein Read10 and the Write10 is taked the means of complete transparent filtration memory device.Response to Read10: obtain the data that computing machine is asked from the USB movable memory equipment earlier, and then be transmitted to computing machine; Response to Write10: direct receiving computer data sent, and then store in the USB memory device.The concrete instantiation procedure of Read10 is seen Fig. 3.
The described file data that identifies the FAT file system of transmitting in the data bunch; It is characteristic according to write store or readout memory data; Judge whether these data are file content in the FAT file system, and the possibility that get rid of comprises: main startup record, DOS start record, file allocation table 1, file allocation table 2, follow catalogue and sub-directory data.There is a common characteristic in DOS file spare system: sub-directory must begin with the file of ". " and " .. " by name.According to the address of aggregate of data and these characteristics just can with more than the data of non-file content foreclose.Indirect realization is to the identification of FAT file system file data.
The described block cache of opening up utilizes the principle of direct mapping address, in the less buffer memory of the capacity that the USB memory device can be mapped to open up.Use address mapping table storage address map information in addition.The data that buffer memory reads recently and writes, the probability of directly asking for to disk when reducing next visit data improves transmission speed.
Described enciphering and deciphering algorithm can be selected concrete encryption standard (must be symmetric cryptography) for use according to actual conditions, encrypts and adopts group mode, initialization vector can utilize the address of current data to generate.Concrete group mode also can be selected for use according to actual conditions.Implementation realizes according to the mode of selecting for use software mode, hardware mode or soft or hard to combine to the actual requirement of speed, cost.
Described key production module; Can select the generation method of key according to actual conditions for use; This module satisfies certain particular user, the use when using key that the inventive method uses and reading when disk writes ciphertext identical, and this key has only validated user to obtain.
Beneficial effect: the file encryption-decryption method of a kind of USB movable memory equipment of the present invention has good functional characteristics: through the analysis to USB physical layer data stream; Realized the encryption of the file-level of file system layer; Guaranteed that disk file name, catalogue exist with the plaintext form, whether file data is expressly to exist the operation of depending on the user; Adopt the mode of the nearest visit data of buffer memory to reduce controller directly obtains data from the USB disk probability, improve whole transfer rate; The AES of employing standard and encryption mode, security performance can be guaranteed.The present invention can be according to user's needs; Optionally use the generation method of key; The key that generates is transferred to the key use of this control module as AES through spare interface; The user that different keys is corresponding different can realize the enciphered data coexistence of a plurality of different users of same disk.In addition; System and cryptographic object, computing machine three's the separate high degree of flexibility that has guaranteed that the USB movable memory equipment uses; Except using as encrypting disk, also can be used as the generic USB memory device and use, borrow mutually to copy mutually to need not all to worry that enciphered data wherein can be cracked.
Description of drawings
Fig. 1 is the general structure synoptic diagram of the inventive method.
Fig. 2 is the block diagram of the inventive method.
Fig. 3 is the transparent transmission synoptic diagram of usb data in the inventive method.
Fig. 4 is the protocol stack synoptic diagram of the transmission of usb data in the inventive method.
Fig. 5 is the theory diagram of the practical implementation case of Fig. 2.
Embodiment
The file encryption-decryption method of USB movable memory equipment of the present invention is connected to computing machine and USB memory device through two USB interfaces, to parsing, the filtration of usb data stream on one of them USB interface, identifies the file data bunch of FAT file system; Through opening up a block cache, adopt the method for directly mapping to shine upon mutually simultaneously, temporary reading recently and the data that write with the address of USB memory device; Then the file data that identifies is used enciphering and deciphering algorithm, and replace the data before the encryption and decryption, turn back to Physical layer at last again, send from another USB interface.Key can obtain from key production module through the port of reserving.
The concrete steps that the present invention comprised are following:
1.USB the parsing of data stream:
The parsing of described usb data stream is divided into enumeration stage and data transfer phase.Enumeration stage with the device description of descending USB device, configuration describe, interface is described, end points is described and character string is described as the response to the various standard request of computing machine.At data transfer phase, the mass storage class standard must follow the appearance order of " order ", " data ", " executing state " of CBW, data, CSW at the form of input and output end points transmitting data, and CBW, CSW have certain criteria.And comprised the command format of SCSI in the CBW data block, only filter out Read10 and two of Write10 change in numerous orders of SCSI, other only do simple forwarding.To with Read10, whether the data of at first judging computer requests in buffer memory, if directly the data of computer requests are being returned; If do not exist, send identical CBW to the USB movable memory equipment, the data that obtain are placed in the buffer memory earlier and the updating memory mapping table, use the data decryption of decipherment algorithm to current request then, and the plaintext after the deciphering is returned to computing machine.For Write10, directly accept the data that computing machine transmits, place it in the buffer memory and the updating memory mapping table, use AES that it is encrypted then, and the ciphertext after will encrypting send in the USB movable storage device with same Writer10 order.
2. identify the file data bunch of FAT file system:
The file data of described FAT file system bunch; According to the FAT file system standard, the data on the storage medium of disk are divided into following several types: main record, DOS startup record, file allocation table 1, file allocation table 2, root directory data, sub-directory data and the file content data of starting.And bunch to be unit, one bunch size is the integral multiple of 512 bytes to file system when locator data.
The described file data that identifies FAT file system in the data transmission bunch; According to the FAT file system standard; The address of file content data must be positioned at after the catalogue, and the root directory root directory that comprises before has: main startup record, DOS start record, file allocation table 1, file allocation table 2 and follow catalogue.The position of these content all is can be according to the address of asking among the SCSI and definite.In addition, in the DOS file system, sub-directory before two filenames must be ". " and " .. ", add their special file attribute and can conclude that this bunch is catalogue data.After the possibility of getting rid of all non-file datas, can conclude that these data are file data.
3. open up buffer memory:
The described buffer memory of opening up utilizes the principle of direct mapping address, in the less buffer memory of the capacity that the USB memory device can be mapped to open up.Use address mapping table to deposit map information in addition.
4. enciphering and deciphering algorithm:
Described enciphering and deciphering algorithm can be selected concrete encryption standard for use according to actual conditions, encrypts and adopts group mode, initialization vector can utilize the address of current data to generate.Concrete group mode also can be selected for use according to actual conditions.Implementation realizes according to the mode of selecting for use software mode, hardware mode or soft or hard to combine to the actual requirement of speed, cost.
5. key production module:
Described key production module can be selected for use as the case may be.Make encrypting module obtain key through making up suitable communication mechanism from key production module.
The present invention has adopted and cryptographic object and the discrete equipment of computing machine; When the user operates disk through intercomputer ground connection, data are carried out real-time encryption and decryption; Obtain key through spare interface; For the common USB memory device provides data encryption feature, and guarantee the normal use of this disk when no encryption device.
The Hardware configuration that instance adopts: ARM chip AT91SAM9260, frequency of utilization 210MHz, processing power 230MIPs, 128M Nand Flash, 64M SDRAM, full speed USB master port, USB is from port for full speed, the SPI interface.The USB movable memory equipment adopts the FAT32 file system.
Below in conjunction with Fig. 5, the structure and the flow process of the inventive method each several part is elaborated.The inventive method is a kind of file encryption-decryption method of USB movable storage device.The practical implementation step is following:
1.USB the parsing of data stream.The host driven of the USB mass storage class of employing complete function and the device drives of USB mass storage class.At first use host driven that the USB movable memory equipment is enumerated, the description that saves as device drives is returned in the description of acquisition, rewrites the Read10 and the Write10 response function of device drives then.
2. identify the file content of the FAT32 file system in the data transmission.Judge according to Read10, the data of Write10 acquisition and the address of data in the step 1 whether these data are file content.
3. open up buffer memory.Utilize the 64M internal memory of system disposition, distribute the 32M internal memory as the data that buffer memory transmits on USB recently, the array of declaring a 128K in addition is as address mapping table.
4. enciphering and deciphering algorithm.Adopt the AES-128 encryption standard, the group mode of CBC.The least unit of encrypting is sector 512 bytes, and the address of adopting current sector is through the initialization vector of the ciphertext after the secret key encryption as CBC.
Actual application result shows, adopts above method can reach the design object of the inventive method fully, and the encryption device of completion has filename, catalogue is visible, the sightless effect of file content.Can be used for realizing the coexistence of ciphertext in same disk that plaintext, different key produce.The encipher-decipher method that adopts has also reached the security intensity of expection.
Should be understood that; Concerning those of ordinary skills; Can be according to the present invention technology preferred embodiment with and technical conceive make various possible changes or replacement, and all these changes or replacement all should belong to the protection domain of accompanying claims of the present invention.
Claims (2)
1. the file encryption-decryption method of a USB movable memory equipment; It is characterized in that; Be connected to computing machine and USB movable memory equipment through master and slave USB interface; Usb data stream to importing on any one USB interface is resolved, is filtered, and identifies the file data of FAT file system; Through opening up a block cache, adopt the method for directly mapping to shine upon mutually simultaneously, temporary reading recently and the data that write with the address of USB movable memory equipment; Then the file data that identifies is used enciphering and deciphering algorithm, and replace the data before the encryption and decryption, turn back to Physical layer at last again, send from another USB interface; Key obtains from key production module through the port of reserving;
Parsing, the filtration of described usb data stream are in same system, to be equipped with main a, driver from two USB interfaces and correspondence, and computing machine is disguised oneself as common " USB movable memory equipment ", respond all computer requests; USB movable memory equipment to be encrypted is disguised oneself as by " computing machine ", change a little according to the computing machine sent request and be transmitted to the USB movable memory equipment once more; This process is divided into two stages, i.e. enumeration stage and data transfer phase; Two USB interfaces of microprocessor controls, one is computer-oriented from interface, another is the main interface towards the USB movable memory equipment; In enumeration stage; Microcontroller is through sending control request to the USB movable memory equipment; Device description, the configuration of obtaining this equipment described, interface is described, end points is described, character string is described and the largest logical unit number, the corresponding requests of using the foregoing description responsive computer that obtains from the USB movable memory equipment to initiate then; At data transfer phase; Microcontroller passes through the analysis to the data of transmitting with Bulk Only transmission mode; Utilize the cannonical format of CBW and SCSI; Identify the order of computing machine, the order beyond wherein Read10 and the Write10 is taked the means of complete transparent filtration the USB movable memory equipment; Response to Read10: obtain the data that computing machine is asked from the USB movable memory equipment earlier, and then be transmitted to computing machine; Response to Write10: direct receiving computer data sent, and then store in the USB movable memory equipment.
2. the file encryption-decryption method of a kind of USB movable memory equipment according to claim 1; It is characterized in that; The described file data that identifies the FAT file system; It is characteristic according to write store or readout memory data; Judge whether these data are file data, and the possibility that get rid of comprises in the FAT file system: main record, DOS startup record, file allocation table 1, file allocation table 2, root directory data and the sub-directory data of starting, preceding 5 can determine one's identity through the address of data; For the sub-directory data, because the regulation sub-directory must be with the file beginning of ". " and " .. " by name in the DOS file system, according to the specific properties that this characteristic and this two sub-directories item are had, its identity can be confirmed.
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| Application Number | Priority Date | Filing Date | Title |
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| CN2009101830691A CN101630292B (en) | 2009-07-29 | 2009-07-29 | File encryption-decryption method of USB removable storage device |
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| CN2009101830691A CN101630292B (en) | 2009-07-29 | 2009-07-29 | File encryption-decryption method of USB removable storage device |
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| CN101630292B true CN101630292B (en) | 2012-02-29 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105656866A (en) * | 2014-12-02 | 2016-06-08 | 华为技术有限公司 | Data encryption method and system |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101799856A (en) * | 2010-03-17 | 2010-08-11 | 太仓市同维电子有限公司 | Method for encrypting application software private area of EVDO (evolution-data optimized) data card end |
| CN102436568B (en) * | 2010-09-29 | 2014-12-17 | 苏州慧尔科技发展有限公司 | Computer external encryption device with storage function and encryption and decryption method utilizing same |
| CN104573573B (en) * | 2014-11-14 | 2017-09-29 | 深圳市芯海科技有限公司 | The data protection system and method for a kind of mobile storage |
| US10049228B2 (en) | 2015-01-20 | 2018-08-14 | Microsoft Technology Licensing, Llc | File encryption support for FAT file systems |
| WO2017218622A1 (en) * | 2016-06-14 | 2017-12-21 | Google Llc | Power link usage indication |
| CN112434320B (en) * | 2020-11-27 | 2023-03-14 | 海光信息技术股份有限公司 | Mass storage device encryption method, main controller and access device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105656866A (en) * | 2014-12-02 | 2016-06-08 | 华为技术有限公司 | Data encryption method and system |
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