羊皮传书 古希腊的斯巴达人将一条1厘米宽、20厘米 左右长的羊皮带,以螺旋状绕在一根特定 粗细的木棍上 6 復大软件学院 LiT
LiJT 6 羊皮传书 • 古希腊的斯巴达人将一条1厘米宽、20厘米 左右长的羊皮带，以螺旋状绕在一根特定 粗细的木棍上
藏头诗 明才子唐伯虎: 我爱兰江水悠悠,爱晚亭上枫叶稠。 ·秋月溶溶照佛寺,香烟袅袅绕经楼。 明朝解缙祝某宰相寿辰进诗: 真真宰相,老老元臣,乌纱戴顶龟鹤遐林. 粗看"密文”,浑然诗句颂扬兼祝愿,福禄寿全有; 细究则密语藏头挖苦带讽刺,诅咒"真老乌龟” 復大软件学院 问题讨论的环境 LiT
LiJT 7 藏头诗 明才子唐伯虎： • 我爱兰江水悠悠，爱晚亭上枫叶稠。 • 秋月溶溶照佛寺，香烟袅袅绕经楼。 明朝解缙祝某宰相寿辰进诗 ： • 真真宰相,老老元臣,乌纱戴顶,龟鹤遐林. – 粗看"密文”,浑然诗句,颂扬兼祝愿,福禄寿全有; 细究则密语藏头,挖苦带讽刺,诅咒"真老乌龟” 问题讨论的环境
Caesar Cipher earliest known substitution cipher by Julius caesar first attested use in military affairs example meet me after the toga party PHHW PH DIWHU WKH WRUD SdUWB 8 復大软件学院 LiT
LiJT 8 Caesar Cipher • earliest known substitution cipher by Julius Caesar • first attested use in military affairs • example: meet me after the toga party PHHW PH DIWHU WKH WRJD SDUWB
d Caesar Cipher Exercise we are students of fudan universit Encrypt? zh duh vwxghgwy r i ixgdq xq l yuv lwb 9 復大软件学院 LiT
LiJT 9 Caesar Cipher Exercise we are students of fudan university zh duh vwxghqwv ri ixgdq xqlyhuvlwb Encrypt?
Terminologies laintext the original message ciphertext -the coded message key-info used in cipher known only to sender/receiver encipher (encrypt)-converting plaintext to ciphertext decipher (decrypt)-recovering plaintext from ciphertext cipher -algorithm for transforming plaintext to ciphertext 復大软件学院 LiT
LiJT 10 Terminologies • plaintext - the original message • ciphertext - the coded message • key - info used in cipher known only to sender/receiver • encipher (encrypt) - converting plaintext to ciphertext • decipher (decrypt) - recovering plaintext from ciphertext • cipher - algorithm for transforming plaintext to ciphertext