[计算机]密码学简介.pptVIP

* * 可加： 前景与展望：新应用（电子投票、电子现金）和量子密码 后续阅读的书 * * 18世纪使用 * 18世纪使用 * 18世纪使用 * * * * * 变长密钥、分组和轮数 * * * * * * * * * * * * 加密所涉及的典型通信环境 * * * * ECB/CBC/OFB/CFB/CTR等 * * * * (gb mod p)a mod p = k (ga mod p)b mod p = k * 如果个人丢失了密钥，或者公司由于粗心/离职/不满员工的问题丢失了密钥 * 秘密共享类似于分割的藏宝图 * 1. the Certificate format version – currently there are 3 versions of X.509 (version 3 is the latest). 2. a Certificate serial number which is a unique number assigned by the CA to insure that duplicate certificates are issued. 3. the signature algorithm field which identifies both the hash method and the public key encryption algorithm used by the CA. 4. the Certificate issuer name. This is given by another international standard, X.500 and specifies the country code and the CA organization code. 5. the validity period which contains the date the certificate first became valid and the date it expires. 6. the subject X.500 name. 7. the subject’s public key and the algorithm used by the subject. 8 and 9. optional they consist of an Issuer Unique Identifier followed by a Subject Unique Identifier. These are used in the case of duplicate X.500 names for either party. 10. the CA’s signature. 挑战 请看如下所示的单码关键词替代密码（已知明文是标准英语） GJXXN GGOTZ NUCOT WMOHY JTKTA MTXOB YNFGO GINUG JFNZV QHYNG NEAJF HYOTW GOTHY NAFZN FTUIN ZANFG NLNFU TXNXU FNEJC INHYA ZGAEU TUCQG OGOTH JOHOA TCJXK HYNUV OCOHQ UHCNU GHHAF NUZHY NCUTW JUWNA EHYNA FOWOT UCHNP HOGLN FQZNG OFUVC NZJHT AHNGG NTHOU CGJXY OGHTN ABNTO TWGNT HNTXN AEBUF KNFYO HHGIU TJUCE AFHYN GACJH OATAE IOCOH UFOXO BYNFG 破译（1） 根据我们的猜测，密钥如下： plain: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z cipher: 证据: 频数表明 N 是 E 连接数据表明 O 是 I 连接数据表明 Y 是 H 连接数据也表明 A 是 O 因而剩下的元音标明U 是 A 常用组合 TH 对表明 H 是 T 元音组合表明 T 是 N 注意: 这只是我们根据 观察得到的猜测 ，可能对也可能 是错的。 U N Y O T A H 破译（2） 在文本和密钥两方面下功夫，可以逐步得到: plain: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z cipher: U N Y O T A H G J X X N G G O T Z N U C O T W M O H Y J T K T A M T X