ST22N256

4/8

The product has two execution modes. Java mode

is used when JavaCard™ 2.x byte codes are be-

ing executed. Native mode is used for long JavaC-

ard™ byte codes, Native methods and system

routines. The processor enters Java mode when a

dispatch (DISP) instruction is encountered. When

executing in Native mode, there are two privilege

levels, User and Supervisor. Some instructions

can only be executed in Supervisor mode.

Instructions are of variable length, from 1 to 4

bytes in Native mode.

Special instructions exist for single-cycle stack op-

erations, a frequent occurrence in Java code.

Short branches and conditional branches within a

1 KByte block or the entire 16-MByte instruction

space are supported. The product has four stages

of pipeline in Native mode: fetch, decode, execute

and write-back. In Java mode, there are five stag-

es of pipeline: byte code-fetch, byte code-decode,

decode, execute and write-back.

The CPU core has 16 32-bit general purpose reg-

isters, as well as special registers of variable

length.

The chip also features a very high performance

Asynchronous Serial Interface (ASI) to support

high speed serial communication protocols com-

patible with ISO 7816 standard.

It is manufactured using the highly reliable ST

CMOS EEPROM technology.

EMBEDDED SOFTWARE

The Hardware Software Interface (HSI) imple-

ments the Hardware abstraction layer. It consists

of C interfaces to the EEPROM memory and pe-

ripherals. The drivers are:

– Non Volatile Memory

– Asynchronous Serial Interface

– Central Interrupt Controller

– Timer

– Random Number Generator

– Clock Manager

– Memory Protection Unit

– Sensors

– Security

Note:

– The HSI driver software layer is a C-oriented

API allowing efficient and secureaccess to the

peripherals and Non Volatile Memory for

programming or erasing.

– Only the OS and JavaCard™ Virtual Machine

(JVM) domains can access the HSI software

layer (In the following the term OS will refer to

the software layer that is directly interfaced to

the HSI).

CRYPTOGRAPHIC LIBRARY

ST proposes a complete set of firmware subrou-

tines. This library is located in a specific ROM ar-

ea. It saves the operating system designer from

coding first layer functions and allows him to con-

centrate on algorithms, Public Key Cryptography

and Secret Key Cryptography protocols imple-

mentation.

The cryptographic library, located in a specific

ROM area, contains firmware functions for:

– basic mathematics including modular

squaring and multiplication for various

lengths;

– modular exponentionation;

– more elaborate functions such as RSA

signatures and verifications for modulo length

up to 2048 bits long;

– full internal key generation for signatures/

verifications. This guarantees that the secret

key will never be known outside the chip and

contributes to the overall system security.

– long random number generation

– SHA-1

– RSA key generation

– DES, Triple DES

– AES-128, AES-192, AES-256