Cryptosystem A cryptosystem is composed of a set (Ee:eEX} consisting of enciphering transformations and the corresponding set (Ee:eeX)={Da:deX) of deciphering transformations.In other words,for eacheK,there erists a unique dK such that Da=E,so that Da(Ee(m))=m for all mM. The keys (e,d)are called a key pair where possibly e=d.A cryptosystem is also called a cipher
Cryptosystem
间题3： 你能香说说一个“好”的 cryptosystem应该是什么 样的？
Kerckhoffs'Rules for Field Ciphers 1.The cryptosystem should be practically unbreakable (breakable in theory, perhaps,but not in practice). 2.A compromised cryptosystem should not inconvenience the correspondents. (This is the one from which his principle,displayed on page 96,seems to be derived since it says that the enemy may know the cryptosystem,but one should still be able to send messages since the enemy cannot cryptanalyze with this knowledge and without the key.) 3.The key should be easy to both remember and change at will. 4.Cryptosystems must be amenable to being sent by telegraph. 5.The mechanisms of the cryptosystem must be easily portable and entirely operable by a single entity. 6.The cryptosystem must be easy to use without reference to any manuals or the need for deep mental effort