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1、 ＤＥＳ算法的安全性及其應用 摘要 ：對DES算法的加密進行分析，提出DES算法安全性問題，介紹了DES算法的應用，指出密鑰的長度、多重DES算法、算法的安全管理、弱密鑰等安全性問題必須給予重視。 關鍵詞 ： DES算法 ； 密鑰 ； 加密 ； 安全性 ； 應用. 數(shù)據(jù)加密標準（Data Encryption standard , DES）是美國國家標準局研究，除美國國防部以外其他部門的計算機系統(tǒng)的數(shù)據(jù)加密標準，屬于分組密碼的一種，在具體的應用中還無法將這種加密算法完全破解掉，因此也被美國政府作為限制出口的一種技術，它目前仍被廣泛使用，具有較高的安全性。 1.DES算法概

2、述 DES是一個對稱算法：加密和解密用的是同一算法（除密鑰編排不同以外），既可用于加密又可用于解密。它的核技術是：在相信復雜函數(shù)可以通過簡單函數(shù)迭代若干圈得到的原則下，利用F函數(shù)及對合等運算，充分利用非線性運算。DES以64位為分組對數(shù)據(jù)加密。每組64位，最后一組若不足64位以“0”補齊。密鑰通常表示為64位的數(shù)，但每個第8位都用作奇偶校驗，可以忽略，所以密鑰的長度為56位，密鑰可以是任意的56位的數(shù)，且可在任意的時候改變。其中極少量的數(shù)被認為是弱密鑰，但能容易地避開它們，所有的保密性依賴于密鑰。 2.DES算法的加密分析 2.1 DES算法的基本思想 DES對64位的明文分組進行操

3、作。通過一個初始置換，將明文分組分成左半部分（L0）和右半部分（R0），各32位長。R0與子密鑰K1進行F函數(shù)的運算，輸出32位的數(shù)，然后與L0執(zhí)行異或操作得到R1，L1則是上一輪的R0，如此經過16輪后，左、右半部分合在一起，經過一個末置換（初始置換的逆置換），這樣該算法就完成了。 2.2 初始置換 初始置換在第一輪運算前執(zhí)行，對輸入分組實施如表1所示的變換（此表應從左向右、從上向下讀）。例如，初始位置把明文的第58位換到第1位的位置，把第50位換到第2位的位置，把第42位換到第3位的位置等等。初始置換和對應的末置換并不影響DES的安全性。它的主要目的是為了更容易地將明文與密文數(shù)據(jù)以字節(jié)

4、大放入DES芯片中。 2.3 子密鑰的生成 子密鑰的產生如圖1所示[1]。將64位密鑰進行密鑰置換，不考慮每個字節(jié)的第8位，DES密鑰由64位減至56位，56位密鑰被分成兩部分，前28位為C0，后28位為D0。 C0＝Ｋ５７Ｋ４９Ｋ４１…Ｋ５２Ｋ４４Ｋ３６， D0＝Ｋ６３Ｋ５５Ｋ４７…Ｋ２０Ｋ１２Ｋ４。 接著，根據(jù)輪數(shù)，C0和D0分別經過LSi循環(huán)左移1位或2位。16次循環(huán)左移的位數(shù)依據(jù)下列規(guī)則進行： 循環(huán)左移位數(shù) １，１，２，２，２，２，２，２，１，２，２，２，２，２，２，１ 經過循環(huán)左移得到的Ci，Di經過壓縮置換即得到子密鑰Ki（ｉ＝１，２，…，16）。壓縮置換也稱

5、作置換選擇，就是從56位中選出48位，表2定義了壓縮置換。例如，處在第33位位置的那一位在輸出時移到了第35位的位置，而處在第 18位位置的那一位被略去。 2.4 16輪迭代過程 ＤＥＳ 算法有16次迭代，迭代如圖2所示[2]。從圖中可得到 ，ｉ＝１，２，３…１５，１６。 Ｆ 函數(shù)的實現(xiàn)原理是將進行擴展置換后其結果與進行異或，并把輸出內容執(zhí)行S盒替代與P盒轉換后得到，其原理如圖3所示[3]。 擴展置換也叫做E盒，它將數(shù)據(jù)右半部分從

6、32位擴展到48位，改變了位的次序，重復了某些位，比原輸入長了16位，數(shù)據(jù)位仍取決于原輸入。擴展置換的48位輸出按順序分成8組，每組6位，分別輸入8個S子盒，每個子盒輸出4 位，共32位。假設將S盒的6位的輸入標記為b1、b2、b3、b4、b5、b6，則b1和b6組合構成了一個2位的數(shù)，從0到3，它對應著S表中的一行。從b2 到 b5構成了一個4位的數(shù)，從0到15，對應著表中的一列，行列交匯處的數(shù)據(jù)就是該S盒的輸出。每個S盒被看作一個4位輸入的代替函數(shù)：b2到b5直接輸入，輸出結果為4位，b1和b6位來自臨近的分組，它們從特定的S盒的4個代替函數(shù)中選擇一個。這是該算法的關鍵步驟，所有其他的運算

7、都是線性的，易于分析，而S盒是非線性的，它比DES其他任何一步提供了更好的安全性。P盒轉換是把每個輸入位映射到輸出位，任意一位不能被映射兩次，也不能被略去。 2.5 末置換 末置換是初始置換的逆過程，DES在最后一輪后，左半部分和右半部分并未交換，而是將R16和L16并在一起形成一個分組作為末置換的輸入。 3 DES算法安全性問題 3.1 DES算法密鑰的長度 最初的羅斯福密碼中密鑰長度為128位，ＤＥＳ的加密單位僅有64位二進制，而且其中某些位還要用于奇偶校驗或其他通訊開銷，有效密鑰只有56位， 這對于數(shù)據(jù)傳輸來說太小，各次迭代中使用的密鑰KI是遞推產生的，這種相關性必然降低了密

8、碼體制的安全性。因此，人們會對56位密鑰的安全性產生質疑，那么56位密鑰是否足夠，已成為人們爭論的焦點之一。 至今，最有效的破解DES算法的方法是窮舉搜約是228，493，000年。但是，仍有學者認為在可預見的將來用窮舉法尋找正確密鑰已趨于可行，所以若要安全保護10年以上的數(shù)據(jù)最好不用DES算法。近年來有人提出用差分和線性攻擊方案來破解DES算法，雖然，從理論上來說破譯的性能高于窮舉搜索法，但要有超高速計算機提供支持，以致于美國國家保密局和計算機科學技術學會組織各界專家研究DES密碼體制的安全性問題后，得出樂觀的結論：沒有任何可以破譯DES密碼體制的系統(tǒng)分析法。若使用窮舉法，則在1990年以

9、前基本上不可能產生出每天能破譯一個DES密鑰的專用計算機。即使屆時能制造出這樣的專用機，它的破譯成功率也只會在0.1到0.2之間，而且造價可能高達幾千萬美元。根據(jù)目前的計算技術和DES的分析情況，16－圈DES（采用16輪迭代）仍然是安全的，但提醒使用者不要使用低于16－圈的DES，特別是10－圈以下的DES。盡管如此，我們仍然需要考慮對DES算法進行改進，使密鑰長度增加些，以實現(xiàn)更好的保密功能。 3.2 多重DES算法 針對DES算法上的缺陷，各國專家們都在研究如何增強DES算法的安全性，現(xiàn)在已發(fā)展出幾十種改進的DES，經過比較，筆者認為多重DES具有較高的可行性。 為了增加密鑰的長度

10、，采用多重DES加密技術，將分組密碼進行級聯(lián)，在不同的密鑰作用下，連續(xù)多次對一組明文進行加密。針對DES算法，專家們的共識是采用3重DES加密算法。3重DES方法需要執(zhí)行3次常規(guī)的DES加密步驟，但最常用的3重DES算法中僅僅用兩個56位DES密鑰。假設這兩個密鑰為K1與K2，其算法的步驟是： １）用密鑰K1進行DES加密； ２）用步驟1的結果使用密鑰K2進行DES解密； ３）用步驟2的結果使用密鑰K1進行DES加密。 這個過程稱為EDE（加密—解密—加密）。 三重DES可使加密密鑰長度擴展到128位，其中有效112位。三重DES的112位密鑰長度在可以預見的將來可認為是合適的、安全

11、的，據(jù)稱，目前尚無人找到針對此方案的攻擊方法。因為要破譯它可能需要嘗試256個不同的56位密鑰直到找到正確的密鑰。但是三重DES的時間是DES算法的3倍，時間開銷較大。 3.3 避開DES算法漏洞,實現(xiàn)安全管理 在DES密鑰KEY的使用、管理及密鑰更換的過程中，應絕對避開DES算法的應用誤區(qū)，即：絕對不能把KEY的第 ８、１６、２４…６４ 位作為有效數(shù)據(jù)位，來對KEY進行管理。從上述DES算法的描述中知道，每個字節(jié)的第8位作為奇偶校驗位以確保密鑰不發(fā)生錯誤，這8位不參與DES運算。因此，特別推薦給金融銀行界及非金融業(yè)界的領導及決策者們，尤其是負責管理密鑰的人，要對此點予以高度重視。有的銀

12、行金融交易網(wǎng)絡，利用定期更換DES密鑰KEY的辦法來進一步提高系統(tǒng)的安全性和可靠性，如果忽略了上述應用誤區(qū)，那么，更換新密鑰將是徒勞的，將威脅到金融交易網(wǎng)絡的安全運行，所以更換密鑰一定要保證新KEY與舊KEY真正的不同即除了第 ８、１６、２４…６４ 位以外其它位數(shù)據(jù)發(fā)生了變化，這樣才能保證DES算法安全可靠發(fā)揮作用，須務必對此保持高度重視。 現(xiàn)代密碼學的特征是算法可以公開。保密的關鍵是如何保護好自己的密鑰，而破密的關鍵則是如何能破解得到密鑰。統(tǒng)的安全主管者，要根據(jù)本系統(tǒng)實際所使用的密鑰長度與其所保護的信息的敏感程度、重要程度以及系統(tǒng)實際所處安全環(huán)境的惡劣程度，在留有足夠的安全系數(shù)的條件下來確

13、定其密鑰和證書更換周期的長短。同時，將已廢棄的密鑰和證書放入黑庫歸檔，以備后用。密鑰更換周期的正確安全策略是系統(tǒng)能夠安全運行的保障，是系統(tǒng)的安全管理者最重要、最核心的日常工作任務。 3.4 弱密鑰 在DES算法中存在12個半弱密鑰和4個弱密鑰。由于在子密鑰的產生過程中，密鑰被分成了2個部分，如果這2個部分分成了全0或全1，那么每輪產生的子密鑰都是相同的，當密鑰是全0或全1，或者一半是1或0時，就會產生弱密鑰或半弱密鑰，DES算法的安全性就會變差。在設定密鑰時應避免弱密鑰或半弱密鑰的出現(xiàn)。 4.DES算法的應用 自DES算法頒布之后，引起了學術界和企業(yè)界的廣泛重視。許多廠家很快生產出實現(xiàn)

14、DES算法的硬件產品，廣大用戶在市場上買到高速而又廉價的DES 硬件產品之后，開始用它加密自己的重要數(shù)據(jù)，從而大大推廣了密碼技術的使用。 DES算法的入口參數(shù)有3個：KEY、DATA、MODE。其中KEY為8個字節(jié)共64位，是DES算法的工作密鑰；DATA也為8個字節(jié)64位，是要被加密或被解密的數(shù)據(jù)；MODE為DES的工作方式，有兩種：加密和解密。 DES算法是這樣工作的：如MODE為加密，則用KEY去把數(shù)據(jù)DATA 進行加密，生成DATA的密碼形式（64位）作為DES的輸出結果；如MODE為解密，則用KEY去把密碼形式的數(shù)據(jù)DATA解密，還原為DATA的明碼形式（64 位）作為DES的輸

15、出結果。在通信網(wǎng)絡的兩端，雙方約定了一致的 KEY，在通信的源點用KEY對核心數(shù)據(jù)進行DES加密，然后以密碼形式在公共通信網(wǎng)（如電話網(wǎng)）中傳輸?shù)酵ㄐ啪W(wǎng)絡的終點，數(shù)據(jù)到達目的地后，用同樣的KEY對密碼數(shù)據(jù)進行解密，便再現(xiàn)了明碼形式的核心數(shù)據(jù)。這樣，便保證了核心數(shù)據(jù)在公共通信網(wǎng)中傳輸?shù)陌踩院涂煽啃訹3]。通過定期在通信網(wǎng)絡的源端和目的端同時改用新的KEY，便能更進一步提高數(shù)據(jù)的保密性，這正是現(xiàn)在金融交易網(wǎng)絡的流行做法。 在.NET開發(fā)系統(tǒng)中，微軟公司提供了DES公用密鑰的加密類，使用它，我們可以自己編制自己的標準DES加密算法。在任何一個單位，程序員只要設計此程序就能對零散離散文件進行加密傳輸

16、，而如果要和其他單位交換數(shù)據(jù)，由于使用的公用算法，只需要向對方提供密鑰及算法說明即可，使用非常方便。 參考文獻 ： ［１］盧開澄．計算機密碼學─計算機網(wǎng)絡中的數(shù)據(jù)保密與安全：第 ３ 版［Ｍ］．北京：清華大學出版社，２００３． ［２］馮登國，吳文玲．分組密碼的設計與分析［Ｍ］．北京：清華大學 出版社，２０００． 畢業(yè)設計(論文) 英文翻譯 題 目 : 基于混合密碼的數(shù)字簽名方案設計 院、系(部): 電子信息工程學院 專業(yè)及班級: 0 7 0 4 0 5 姓 名: 劉 軍 飛

17、 學 號: 070405114 指 導 教師: 張 艷 玲 日 期: 2011.05.02 DES algorithm safety and its application Abstract: the encryption algorithm for DES, the article analyzes the safety problems DES algorithm is introduced, and points out that the application

18、of the proposed algorithm is DES key lengths, multiple DES algorithm, algorithm of safety management, such as weak key safety problems must be addressed. Keywords: DES algorithms; Key; Encryption; Safety; application Data encryption standard (DES) is the U.S. national bureau of outside the U.S.

19、defense department, in addition to other departments of the computer system data encryption standard, belongs to a block cipher in the specific application, still unable to break the encryption algorithm, so completely off by the United States government as a technology export restrictions, it is st

20、ill widely used, has higher security. 1 DES algorithm overview DES is a symmetric algorithm: encryption and decryption is the same algorithm with (except the key organises different outside), can be used not only can be used to encrypt and decrypt. It is the core technology in believe complex func

21、tion can: through simple iterative several laps () function gets under the principle of DuiGe using F function and such operations, make full use of nonlinear operations. DES to 64-bit data encryption for grouping. Each group 64-bit, if one last set of less than 6 bits to "0" fill neat. Key usually

22、expressed as a 64-bit number, but each article 8 bits are used as parity and can be ignored, so dense length is 56, key can be arbitrary 56 number, and can in any time change. One of very few number is considered weak key, but can easily avoid them, all the secrecy dependent on the keys. 2 DES algo

23、rithm encryption analysis 2.1The basic idea of 210 DES algorithm DES 64-bit expressly grouping of operation. Through an initial displacement, will expressly group into left brain part (L0) and the right-side part (R0), each 32 bits long. R0 and son key K1 used, and on F function output 32-bit numb

24、er, then and L0 executive xor operator get R1, L1 is the last round R0, so after 16 rounds, left, right after partial together, after a late replacement (initial displacement inversereplacement), so this algorithm is completed. 2.2 initial displacement Initial displacement in the first round of in

25、put, former executive computing group implement such as table 1 shows transform (this form should, from left to right to read) for example, the initial position of the proclaimed to the 58th a change of position, one of the first 50 change to second place position, put the first 4 to third position,

26、 etc. Initial displacement and the corresponding end displacement does not affect the safety of DES. Its main purpose is to will be more easily with ciphertext data in bytes written in DES chip the size. 2.3The key to generate son The key to produce as shown in figure 1 son shown [1]. Will 64-bit

27、decryption key, dont consider key replacement each byte number eight, DS keys consists of a 64-bit to 56, 56 key is divided into two parts, the first 28 bits after C0, for 28 for D0. C0 = K57K49K41... K52K44K36, D0 = K63K55K47... K20K12K4. Then, according to round number, C0 and D0 LSi cycle respect

28、ively after moves left in 1 or 2 bits. 16 times cycle of digit moves left the following rules: cycle according 1,1,2,2,2,2,2,2,1,2,2,2,2,2,21 left shift several. After cycle of Ci, moves left get Di after compression replacement namely get son Ki (I = 1 key,..., 16). Compression replaceme

29、nt also called replacement choice, is selected from 56 48 bits, table 2 defines compression replacement. For example, in the positions is 33 output moved in a position of # 35 in 18th place, and that a position omitting . 2.4 16 iteration process DES algorithm has 16 iterations, the iterative as f

30、igure2shows [2]. From the graph can get Li = Ri - 1, Ri = Li - 1 ⊕ F (Ri - 1, Ki), I = 1, 2, 3... 15,16. F function realization principle is to expand Ri - 1 Ki after displacement and the results are different, and the output content or executive S box of alternative

31、 and P box after converting get F (Ri - 1, Ki), ts principle fig.03 shows [1]. Expand replacement also called E box, it will data from the right part 32-bit expanded to 48 bits, changed a sequence, repeat some bits, compared to the original input long 16, data bits, still depends on the original inp

32、ut. Extension of the replacement of 48 bits in sequence into eight groups output, each group of six, eight S respectively input son box, each child box output four, a total of 32. Assumptions will S box six input marked b1, b2, b3, b4,b5, b6, then b1 and b6 constitute a 2 bits number, from 0 to 3, i

33、t corresponds to S the line. Watch From b2 to b5 constituted a 4 digit number, from 0 to 15, corresponding to table a column in the ranks of the data interchange, is that the S box output. Each S box can be viewed as a four input to replace function: b2 to b5 direct input, output results for four, b

34、1 and b6 participants from neighboring grouping, them from specific S box 4 instead of function choose a. This is the key step in the algorithm, and all other operations are linear, easy to analysis, and S box is nonlinear, it any other step than DES provides better security. P boxes each input a tr

35、ansition is mapped to output a, any one cannot be mapped twice, also cannot be cut out. 2. 5 end displacement The replacement of the initial replacement is the inverse process,DES during the last round, right and left parts, but will not exchange part R16 and L16 and together to form a group as th

36、e input end displacement. 3 DES algorithm safety issues 3.1 DES algorithm key lengths Initial Roosevelt password for 128-bit key length, DES56 bits, this is too small for data transmission, the keys used in every iteration of the recursive Ki is produced, this correlation inevitable reduces the p

37、assword system security. Therefore, people will to 56 keys have cast doubt on the safety, then 56 key whether enough, has become one of the focuses of debate. So far, the most effective cracked DES algorithm method is exhaustively search method. 56 need 228,493,000 years is about. Still, some schol

38、ars think in the foreseeable future exhaustion method with finding the right key has already become more and more feasible, so if want security protection of 10 years of above data had better not use DES algorithm. In recent years some proposed with difference and linear attac

39、k scheme to crack, though, from DES algorithm theoretically decipher than the performance Exhaustively search method, but must have the super-fast computers provide support, that American state secrecy bureau and computer science and technology institute organizing. World experts research DES passw

40、ord system, it is concluded that the problem of safety in the conclusion of optimism after: without any can decipher DES password system system analysis. If use exhaustively method, is in before 1990 basically impossible to produce each day to decipher a DES key special computer. Even when can produ

41、ce such steels, it will only in deciphering success rate between 0.1 to 0.2, and cost could be as high as millions dollars. According to the present computing and DES analysis situation, 16 - circle DES (with 16 iteration) is still safe, but warn users dont use less than 16 - circle DES, especially

42、10 - circle the following DES. Nevertheless, we still need to consider to DES algorithm was improved, add some key length, in order to achieve better confidential function. 3. 2 multiple DES algorithm Aimed at the defects of algorithm, DES nations experts are studying how to enhance the security o

43、f DES algorithm, has now developed dozens of improved DES, after comparison, the author thinks that multiple DES has the high feasibility. In order to increase the key lengths, using multiple DES encryption technology group password, cascade, in a different key function, continuous Many times for a

44、 group of plaintext encrypted. According to the experts, DES algorithm adopts triple DES consensus is encryption algorithm. Triple DES method needs to perform three conventional DES encrypted steps, but the most commonly used three heavy DES algorithm using only two 56 DES keys. Suppose this two key

45、s with K2, its algorithm triassic-paleogene the steps are: 1) for DES encrypted with key K1; 2) the results in step 1 to use a key K2 to DES decryption; 3) the results in step 2 to use a key K1 for DES encrypted. This process is called EDE (encryption - decryption - encryption). Triple DES can

46、make the encryption key length expanded to 128-bit, including effective 112. The 112 triple DES key length in the foreseeable future can think is appropriate, safe, allegedly, at present there is no people find in this scheme method of assault. Because want Decipher it may need to try to 256 differe

47、nt 56 key until you find the right key. But triple DES time is three times the DES algorithm, time consuming is bigger. 3.3 avoid DES algorithm loophole, realize safe management In DES keys use and management of the Key specific and Key changes process, should absolutely avoid DES algorithm applic

48、ation pitfalls, namely: definitely not the Key specific section 8, 16, 24... 64 bit as valid data bits, to manage to Key specific. From the description of the above DES algorithm, each byte of the first that eight as parity to ensure the key not errors occur, the eight not participation DES operatio

49、ns. Therefore, particularly recommended for financial banking and non-financial industry leadership and decision makers, especially responsible for managing the people, which key point pay serious attention. Some Banks financial transaction network, use change regularly DES keys to Key specific to f

50、urther improve reliability and safety of the system, if you ignore the above application pitfalls, then, change the new Key will be in vain, and threaten financial transaction network safety running, so change Key must ensure new Key specific and old Key specific real different that, in addition to

51、the first 8, 16, 24... 64 bit beyond other bits of data changed, so that we can guarantee DES algorithm safe and reliable work, must make sure to keep high attention. Modern cryptography features is algorithm can open. The key is how to protect the confidentiality of their keys, and the key is brok

52、en secret key. How can get hacking The security of the system, this system according to the director of the actual use of key length and the sensitive degree of protection of information, important degree and the actual place security environment system of degree, in bad with sufficient safety coeff

53、icient conditions from determine its key and certificate change cycle length. Meanwhile, will have abandoned key and certificate in black library archive, away for future use. Key change cycle right security strategy is system can safe operation of the systems safety protection, is the most importan

54、t and the most managers of daily tasks. 3.4 weak keys In DES algorithm 12 and a half exists weak key and four weak keys. Because the key in the son produced process, the key is divided into 2 parts, if this 2 parts into full 0 or total 1, so each wheel produces daughter keys are the same, and when

55、 keys are all 0 or 1, or half full 1 or 0, can produce weak keys, or half a weak the safety of keys, DES algorithm will become poor. In setting key should avoid weak keys, or half a weak key to appear. 4 DES use of the algorithm After since DES algorithm, caused promulgated by academic and corpora

56、te attention. Many manufacturers soon produce realize DES algorithm Hardware products, users in the market to buy high speed and cheap DES hardware products, to start using it after the important data encryption himself, thus greatly promote the use of a password techniques. DES algorithm entry par

57、ameters have 3: Key specific, Data, Mode. One Key specific for 8 byte 64 bits, which is the Key; DES algorithm work Data also for 8 byte 64-bit, is to be encrypted or message decrypted Data; Mode for DES way of working, have two kinds: encryption and decryption. DES algorithm is how it works: such a

58、s Mode for encryption, then use the Data to Key specific Data encrypt Data and generate the password form (64 bits); the output as DES Such as Mode for decryption, from the password form to Key specific Data declassified, restore Data for the Data related forms (64 bits) as the output results. DES I

59、n communication network, the parties have agreed on the ends of the agreement in communication, Key specific source point of core data with Key specific, and then taking DES encrypted password form in public communication network (such as network) in the end of transmission to communication network,

60、 data arrived at their destination, with the same Key specific data of password decryption, he portrays plain code forms of core data. So, then guaranteed the core data (such as PIN, MAC, etc) in public communication network security and reliability of the transmission of [3]. Through regularly in t

61、he communication network in the source end and purpose in the switch to the new Key specific, can further improve the data privacy, this is now the financial trading network vogue. In development system, Microsoft provides DES public key encryption class, use it, and we can prepare yourself Standa

62、rd DES encryption algorithm. In any one unit, the programmer as long as this program can design of scattered discrete files for encryption loses. If you want to exchange the data and other units, due to the use of public algorithm, only need to provide each other key and algorithm specification can,

63、 use very convenient. References: [1] Wilkinson j h.algebraic eigenvalue problem. Computer data in a computer network ─ cryptography secrecy and security: the first 3 edition [M]. Beijing: tsinghua university press, 2003. [2]. WuWenLing block cipher FengDengGuo, the design and analysis [M]. Beijing: tsinghua university Press, 2000. [3] DuanWei YangMao phosphorus, ge yong, postgraduate for PhD. The password algorithms and its application in military communication [J].journal of fire Force command and control, 2006 (3) : 68-71.