摘要:本文专注于量子密钥分配和位承诺协议,特别讨论它们的安全性,首先回顾了经典密码学的相关内容,随后对量子密码学进行介绍,并说明其应用领域及存在的问题,最后得出结论并对前景进行展望。
. A decade later, building upon this work, Charles H. Bennett, of the IBM Thomas J. Watson Research Center, and Gilles Brassard, of the Universities de Montréal, proposed a method for secure communication based on Wiesner's “conjugate observables”. In 1990, independently and initially unaware of the earlier work, Artur Ekert, then a Ph.D. student at Wolfson College, University of Oxford, developed a different approach to quantum cryptography based on peculiar quantum correlations known as quantum entanglement.
3、经典密码学——3. CLASSICAL CRYPTOGRAPHY
We present just the basic definition of a cryptosystem and give one example of a classical encryption method, the one-time pad.
3.1 DEFINITION OF CRYPTOSYSTEM
A (deterministic, symmetric) cryptosystem is a five-tipple (P, C, K, E, D) satisfying the following conditions:
P is a finite set of possible plaintexts.
C is a finite set of possible cipher texts.
K is a finite set of possible keys.
For each k Ñ” K, there are an encryption rule ek Ñ” E and a corresponding decryption rule dk Ñ” D, where ek: Pa†’ C and dk: Ca†’ P are functions satisfying dk (ek (x)) = x for each plaintext element x Ñ” P.
In the basic scenario in cryptography, we have two parties who wish to communicate over an insecure channel, such as a phone line or a computer network. Usually, these parties are referred to as Alice and Bob. Since the communication channel is insecure, an eavesdropper, called Eve, may intercept the messages that are sent over this channel. By agreeing on a secret key k via a secure communication method, Alice and Bob can make use of a cryptosystem to keep their information secret, even when sent over the insecure channel. This situation is illustrated in Fig 1.1.
The method of encryption works as follows. For her secret message m, Alice uses the key k and the encryption rule ek to obtain the cipher text c = ek (m). She sends Bob the cipher text c over the insecure channel. Knowing the key k, Bob can easily decrypt the cipher text by the decryption rule dk: dk (c) = dk (ek (m)) = m. Knowing the cipher text c but missing the key k, there is no easy way for Eve to determine the original message m. There exist many cryptosystems in modern cryptography to transmit secret messages. An early well-known system is the one-time pad, which is also known as the Vernam cipher. The one-time pad is a substitution cipher. Despite its advantageous properties, which we will discuss later on, the one-time pad's drawback is the costly effort needed to transmit and store the secret keys.
A B C D E .X Y Z ! - .
0001020304.23242526272829
Fig.3.1 Letters and punctuation marks encoded by numbers from 0 to 29
3.2 ONE-TIME PAD
For plaintext elements in P, we use capital letters and some punctuation marks, which we encode as numbers ranging from 0 to 29, see Fig.3.2.
As is the case with most cryptosystems, the cipher text space equals the plaintext space. The key space K also equals P, and we have P =C= K= {0, 1 . . . 29}. Next, we describe how Alice and Bob use the one-time pad to transmit their messages. A concrete example is shown in Fig.3.2. Suppose Alice and Bob share a joint secret keykof length n= 12, where each key symbol kie {0, 1 . . . 29} is chosen uniformly at random. Le
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