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对称加密算法-DES以及DESede算法
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一、簡述
? 對稱加密算法就是能將數(shù)據(jù)加解密。加密的時候用密鑰對數(shù)據(jù)進行加密，解密的時候使用同樣的密鑰對數(shù)據(jù)進行解密。
? DES是美國國家標準研究所提出的算法。因為加解密的數(shù)據(jù)安全性和密鑰長度成正比。des的56位的密鑰已經(jīng)形成安全隱患，在1998年之后就很少被采用。但是一些老舊的系統(tǒng)還在使用。因為這個des算法并沒有被美國標準委員會公布全部算法，大家一致懷疑被留了后門。所以慢慢就被淘汰掉了。
? 后來針對des算法進行了改進，有了三重des算法（DESede）。針對des算法的密鑰長度較短以及迭代次數(shù)偏少問題做了相應改進，提高了安全強度。不過desede算法處理速度較慢，密鑰計算時間較長，加密效率不高問題使得對稱加密算法的發(fā)展不容樂觀。
二、交互模型
1、消息傳遞雙方約定密鑰，通常由消息發(fā)送方（甲方）構建密鑰通知消息接收方（乙方）
2、甲方使用密鑰對數(shù)據(jù)記性加密，然后將加密后的數(shù)據(jù)通過網(wǎng)絡傳送給乙方
3、乙方接收到數(shù)據(jù)，然后使用約定的密鑰對數(shù)據(jù)進行解密
?
整個模型很像hmac的數(shù)據(jù)交互過程，都是一個密鑰的概念，而且密鑰都是雙方知道的。但是hmac算法是信息摘要的獲取。這邊是對數(shù)據(jù)進行加解密
?
三、java6和bouncycastle針對des算法的數(shù)據(jù)加密支持還是不同的。體現(xiàn)在密鑰長度，工作模式以及填充方式上。這里bouncycastle的密鑰長度是64位。不過在DESede算法上bouncy castle也是密鑰長度比java6的密鑰長度要長。
??? 不過所有的對稱加密算法的實現(xiàn)還是類似的?？梢詤⒖慈缦碌拇a：
1、des算法
[java] view plaincopy
package?com.ca.test;??import?java.security.Key;??import?javax.crypto.Cipher;??import?javax.crypto.KeyGenerator;??import?javax.crypto.SecretKey;??import?javax.crypto.SecretKeyFactory;??import?javax.crypto.spec.DESKeySpec;??import?org.apache.commons.codec.binary.Base64;???????public?class?DESCoder?{???????????????public?static?final?String?KEY_ALGORITHM="DES";????????????????????public?static?final?String?CIPHER_ALGORITHM="DES/ECB/PKCS5Padding";??????????????????????public?static?byte[]?initkey()?throws?Exception{??????????????????????????????KeyGenerator?kg=KeyGenerator.getInstance(KEY_ALGORITHM);????????????????????kg.init(56);????????????????????SecretKey?secretKey=kg.generateKey();????????????????????return?secretKey.getEncoded();??????}????????????????public?static?Key?toKey(byte[]?key)?throws?Exception{????????????????????DESKeySpec?dks=new?DESKeySpec(key);????????????????????SecretKeyFactory?keyFactory=SecretKeyFactory.getInstance(KEY_ALGORITHM);????????????????????SecretKey?secretKey=keyFactory.generateSecret(dks);??????????return?secretKey;??????}???????????????????????public?static?byte[]?encrypt(byte[]?data,byte[]?key)?throws?Exception{????????????????????Key?k=toKey(key);????????????????????Cipher?cipher=Cipher.getInstance(CIPHER_ALGORITHM);????????????????????cipher.init(Cipher.ENCRYPT_MODE,?k);????????????????????return?cipher.doFinal(data);??????}?????????????????public?static?byte[]?decrypt(byte[]?data,byte[]?key)?throws?Exception{????????????????????Key?k?=toKey(key);????????????????????Cipher?cipher=Cipher.getInstance(CIPHER_ALGORITHM);????????????????????cipher.init(Cipher.DECRYPT_MODE,?k);????????????????????return?cipher.doFinal(data);??????}???????????????public?static?void?main(String[]?args)?throws?Exception?{??????????String?str="DES";??????????System.out.println("原文："+str);????????????????????byte[]?key=DESCoder.initkey();??????????System.out.println("密鑰："+Base64.encodeBase64String(key));????????????????????byte[]?data=DESCoder.encrypt(str.getBytes(),?key);??????????System.out.println("加密后："+Base64.encodeBase64String(data));????????????????????data=DESCoder.decrypt(data,?key);??????????System.out.println("解密后："+new?String(data));??????}??}??控制臺輸出結果：??原文：DES??密鑰：ocewbYVbtmE=??加密后：w6KsVSkLV3Q=??解密后：DES??
2、desede算法演示
[java] view plaincopy
package?com.ca.test;??import?java.security.Key;??import?javax.crypto.Cipher;??import?javax.crypto.KeyGenerator;??import?javax.crypto.SecretKey;??import?javax.crypto.SecretKeyFactory;??import?javax.crypto.spec.DESedeKeySpec;??import?org.apache.commons.codec.binary.Base64;???????public?class?DESedeCoder?{??????????????public?static?final?String?KEY_ALGORITHM="DESede";????????????????????public?static?final?String?CIPHER_ALGORITHM="DESede/ECB/PKCS5Padding";??????????????????????public?static?byte[]?initkey()?throws?Exception{??????????????????????????????KeyGenerator?kg=KeyGenerator.getInstance(KEY_ALGORITHM);????????????????????kg.init(168);????????????????????SecretKey?secretKey=kg.generateKey();????????????????????return?secretKey.getEncoded();??????}????????????????public?static?Key?toKey(byte[]?key)?throws?Exception{????????????????????DESedeKeySpec?dks=new?DESedeKeySpec(key);????????????????????SecretKeyFactory?keyFactory=SecretKeyFactory.getInstance(KEY_ALGORITHM);????????????????????SecretKey?secretKey=keyFactory.generateSecret(dks);??????????return?secretKey;??????}???????????????????????public?static?byte[]?encrypt(byte[]?data,byte[]?key)?throws?Exception{????????????????????Key?k=toKey(key);????????????????????Cipher?cipher=Cipher.getInstance(CIPHER_ALGORITHM);????????????????????cipher.init(Cipher.ENCRYPT_MODE,?k);????????????????????return?cipher.doFinal(data);??????}?????????????????public?static?byte[]?decrypt(byte[]?data,byte[]?key)?throws?Exception{????????????????????Key?k?=toKey(key);????????????????????Cipher?cipher=Cipher.getInstance(CIPHER_ALGORITHM);????????????????????cipher.init(Cipher.DECRYPT_MODE,?k);????????????????????return?cipher.doFinal(data);??????}???????????????public?static?void?main(String[]?args)?throws?Exception?{??????????String?str="DESede";??????????System.out.println("原文：/t"+str);????????????????????byte[]?key=DESedeCoder.initkey();??????????System.out.println("密鑰：/t"+Base64.encodeBase64String(key));????????????????????byte[]?data=DESedeCoder.encrypt(str.getBytes(),?key);??????????System.out.println("加密后：/t"+Base64.encodeBase64String(data));????????????????????data=DESedeCoder.decrypt(data,?key);??????????System.out.println("解密后：/t"+new?String(data));??????}??}??控制臺輸出結果：??原文：?DESede??密鑰：?BBDmwTjBsF7IwTIyGWt1bmFntRyUgMQL??加密后：????FM/DsEv3KgM=??解密后：????DESede??
四、總結
1、主要看設定密鑰的長度的變化。同時，bouncycastle支持更多的填充模式，在相同算法上比java6實現(xiàn)的版本的密鑰長度要長
2、java的api中僅僅提供了DES,DESede和PBE 3三種對稱加密算法密鑰材料實現(xiàn)類
總結
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