文档介绍：Miscellaneous Topics
Buy a rifle, encrypt your data, and wait for the
revolution
Smart Cards
Invented in the early 1970’s
Technology became viable in early 1980’s
Major use is prepaid telephone cards (hundreds of millions)
• Use a one-way (down) counter to store card balance
Other uses
• Student ID/library cards
• Patient data
• Micropayments (bus fares, photocopying, snack food)
Memory Cards
Usually based on I2C (serial memory) bus
Typical capacity: 256 bytes
EEPROM capabilities
• Nonvolatile storage
• 10,000 write/erase cycles
• 10ms to write a cell or group of cells
Cost: $5
Microprocessor Cards
ROM/RAM contains card operating system and working
storage
EEPROM used for data storage
Microprocessor Cards (ctd)
Typical specifications
• 8-bit CPU
• 16K ROM
• 256 bytes RAM
• 4K EEPROM
Size ratio of memory cells:
RAM = 4× EEPROM size
= 16× ROM size
Cost: $5-50 (with crypto accelerator)
Smart Card Technology
Based on ISO 7816 standard, which defines
• Card size, contact layout, electrical characteristics
• I/O protocols
– Byte-based
– Block-based
• File structures
File Structures
Files addressed by 16-bit file ID (FID)
• FID is often broken into DF:EF parts (MF is always 0x3F00)
Files are generally fixed-length and fixed-format
File Types
Transparent
• Binary blob
Linear fixed
• n × fixed-length records
Linear variable
• n records of fixed (but different) lengths
Cyclic
• Linear fixed, oldest record gets overwritten
Execute
• Special case of transparent file
File Attributes
EEPROM has special requirements (slow write, limited
number of write cycles) which are supported by card
attributes
• WORM, only written once
• Multiple write, uses redundant cells to recover when some cells
die
• Error detection/correction capabilities for high-value data
• Error recovery, ensures atomic file writes
– Power can be removed at any point
– plex buffering and state handling
mands
mand