计算机问题求解一论题4-4密码算法2017年04月05日
计算机问题求解 – 论题4-4 - 密码算法 2017年04月05日
问题1：Cryptosystem是什么意思？它要解决的基本问题是什么？
最古典：Caesar'sCipherPlainha6a9i3KCKDEFLMGHOPCipherTPlaintuUwn0psayNqRSTWXYZBCQUVACipher6d于hikcei1gIm567823910411120ts0<wanpqy216182213151719202123242514Cipher=Plain+3mod26你试试：WKHGLHLVFDVWThedieiscast!
最古典: Caesar’s Cipher Cipher = Plain + 3mod 26 你试试: WKH GLH LV FDVW The die is cast!
问题2：你能不能用数学概念来描述加密和解密？
TransformationsAn enciphering transformation (also called an enciphering function) is abijective functionE: M- c.where the key e E K uniquely determines Ee acting upon plaintert message unitsmEMto getcipherteatmessageunitsE(m)=cec.A deciphering transformation (or deciphering function) is a bijectiue functionDa: C-M.which is uniguely determined by a given key d E K, acting upon ciphertertmessageunits cEC to getplainteatmessageunitsDa(c) =m.The application of Ee to m, namely the operation Ee(m), is called encipheringencoding, or encrypting m e M, whereas the application of Da to c is calleddeciphering,decoding,ordecrypting cEC
Transformations