Design And Implementation Of SD Memory Disk With Partition Encryption

SD card is a a flash memory storage device based on semi-conductor,which has a lot of advantages,such as small size,large storage capacity,fast speed,so it has been widely used in various types of electronic products.However,the SD memory disk stores data in the form of plain text,which has the risk of information disclosure and being tampered with.Based on above,this thesis realizes access control and hardware encryption of the SD memory disk,and achieves the purpose of data protection.Firstly,this thesis analyzes SD interface protocol,studies the encryption principle of Triple Data Encryption Algorithm(3DES)and Advanced Encryption Standard(AES),and makes a comparison of these two algorithms.Then,according to the current market demand,one kind of new partition encryption SD memory disk design scheme is proposed,which integrates external authentication and partition switching.The S281 is adopted as main controller and 4GB MLC type NAND Flash as data storage in this system and it realizes partition encryption SD memory disk's hardware design.This thesis also introduces the design and implementation of partition encryption SD memory disk's software in detail,which includes the design of firmware and application.The firmware design includes implementation of SD protocol,operation of Flash chip,external authentication,partition switching and full data encryption.In this thesis,using of the address mapping table to solve the problem of dynamic management of bad blocks and realize wear-leveling of Flash,which extends the life of Flash and improves the data transfer rate meanwhile.The application is developed based on Android operating system,users can enter the correct password via the application to access the confidential data which is stored in the SD memory disk.In order to satisfy the various needs of users,this thesis divides the disk-stored space of SD memory disk into public partition and security partition.It defaults display the public partition when power-on,after the successful external authentication,the partition encryption SD memory disk can switch into security partition,one partition at one time.The external authentication is implemented by 3DES,and data in the SD memory disk is encrypted by AES256.To achieve double protection of data security,the passwords after encryption are stored in the Flash randomly.Moreover,the SD memory disk also has the function of modifying passwords,promoting data storage security and flexibility of password use.Ultimately,make the test of the entire system.The experimental results show that the SD memory disk meet the design requirement on data transfer rate,stability and functionality which has practical applications to some extent.