Digital Signatures and Message Authentication Code (MAC) overview Suppose Alice and Bob share a secret key k which determines hash function hk Alice sends (x, y) to Bob where y = hk

Definitions – Digital Signature - a data string which associates a message with some originating entity – Digital Signature Generation Algorithm – a method for producing a digital signature – Digital signature verification algorithm - a method for verifying that a digital signature is authentic (i.e., was indeed created by the specified entity)

Modular arithmetic – Used to define a finite field – a = b mod n means that if a and b are divided by n they produce the same remainder – a*b mod n can result in 0 even if a and b are not 0

Iterating Block ciphers Definition A product cipher combines two or more transformations in a manner intending that the resulting cipher is more secure than the individual components. Definition An iterated block cipher is a block cipher involving the sequential repetition of an internal function called a round function. Parameters include the number of rounds Nr, the block bitsize n, and the bitsize k of the input key K from which Nr subkeys Ki (round keys) are derived. For invertibility (allowing unique decryption), for each value Ki the round function is a bijection on the round input

Originally designed to be efficient in hardware . A LOT of money has been invested in hardware. although DES standard is public there was considerable controversy over design – in choice of 56-bit key (vs Lucifer 128-bit) – and because design criteria were classified

Additional key-sizes and block-sizes Ability to function efficiently and securely in a wide variety of platforms and applications low-end smartcards, wireless: small memory requirements IPSec, ATM – small key setup time in hardware B-ISDN, satellite communication – large encryption speed Flexibility

Cryptographic protocol – Distributed algorithm – Based on cryptographic building blocks – To achieve a security related goal Examples: – Entity Authentication – Key Establishment:Key Distribution(Key enveloping, Key transport), Key agreement – Electronic Payment

6.1 对象指针和对象引用 6.2 对象数组和对象指针数组 6.3 常对象和常成员 6.4 子对象和堆对象

5.1 类的定义 5.2 对象的定义 5.3 对象的初始化 5.4 成员函数的特征

4. 1 函数的定义和说明 4. 2 函数的调用 4.3 函数参数 4.4 内联函数