Public-Key Cryptography probably most significant advance in the 3000 year history of cryptography uses two keys -a public a private key asymmetric since parties are not equal uses clever application of number theoretic concepts to function complements rather than replaces private key crypto 復大软件学院 LiT
LiJT 11 Public-Key Cryptography • probably most significant advance in the 3000 year history of cryptography • uses two keys – a public & a private key • asymmetric since parties are not equal • uses clever application of number theoretic concepts to function • complements rather than replaces private key crypto
Histo public invention due to Whitfield Diffie& Martin hellman at stanford uni in 1976 known earlier in classified community note: now know that Williamson(UK CESG) secretly proposed the concept in 1970 Diffie-Hellman Key EXchange 12 復大软件学院 LiT
LiJT 12 History • public invention due to Whitfield Diffie & Martin Hellman at Stanford Uni in 1976 – known earlier in classified community. – note: now know that Williamson (UK CESG) secretly proposed the concept in 1970 • Diffie-Hellman Key Exchange
公开密钥加密系统 一个公开密钥系统由六要素组成: 明文 公开和私有密钥 加密算法 密文 ◎解密算法 復大软件学院 LiT
LiJT 一个公开密钥系统由六要素组成： 明文 公开和私有密钥 加密算法 密文 解密算法 公开密钥加密系统
开密钥加密 o参与方B容易通过计算产生出一对密钥(公开密 钥KUb,私有密钥KRb) 发送方A很容易计算产生密文C=Ek(M 接收方B通过计算解密密文M=D(O)=Dk[Ekb(M 敌对方即使知道公开密钥KUb,要确定私有密钥 KRb在计算上是不可行的 敌对方即使知道公开密钥KUb和密文C,要确定 明文M在计算上是不可行的 密码对互相之间可以交换使用M= DKRhLEKU(MO=DkEK(QM 復大软件学院 LiST
LiJT 参与方B容易通过计算产生出一对密钥（公开密 钥KUb ，私有密钥KRb ） 发送方A很容易计算产生密文 接收方B通过计算解密密文 敌对方即使知道公开密钥KUb ，要确定私有密钥 KRb 在计算上是不可行的 敌对方即使知道公开密钥KUb 和密文C，要确定 明文M在计算上是不可行的 密码对互相之间可以交换使用 C E (M) KUb 公开密钥加密 M D (C) D [E (M)] KRb KRb KUb M D [E (M)] D [E (M)] KRb KUb KUb KRb