RSA
这种算法1978年就出现了，它是第一个既能用于数据加密也能用于数字签名的算法。它易于理解和操作，也很流行。算法的名字以发明者的名字命名：Ron Rivest, AdiShamir 和Leonard Adleman。
这种加密算法的特点主要是密钥的变化，上文我们看到DES只有一个密钥。相当于只有一把钥匙，如果这把钥匙丢了，数据也就不安全了。RSA同时有两把钥匙，公钥与私钥。同时支持数字签名。数字签名的意义在于，对传输过来的数据进行校验。确保数据在传输工程中不被修改。
流程分析：
甲方构建密钥对儿，将公钥公布给乙方，将私钥保留。 甲方使用私钥加密数据，然后用私钥对加密后的数据签名，发送给乙方签名以及加密后的数据；乙方使用公钥、签名来验证待解密数据是否有效，如果有效使用公钥对数据解密。 乙方使用公钥加密数据，向甲方发送经过加密后的数据；甲方获得加密数据，通过私钥解密。
按如上步骤给出序列图，如下：
通过java代码实现如下：Coder类见 Java加密技术（一）
Java代码 importjava.security.Key;importjava.security.KeyFactory;importjava.security.KeyPair;importjava.security.KeyPairGenerator;importjava.security.PrivateKey;importjava.security.PublicKey;importjava.security.Signature;importjava.security.interfaces.RSAPrivateKey;importjava.security.interfaces.RSAPublicKey;importjava.security.spec.PKCS8EncodedKeySpec;importjava.security.spec.X509EncodedKeySpec;importjava.util.HashMap;importjava.util.Map;importjavax.crypto.Cipher;/***RSA安全编码组件**@author梁栋*@version1.0*@since1.0*/publicabstractclassRSACoderextendsCoder{publicstaticfinalStringKEY_ALGORITHM="RSA";publicstaticfinalStringSIGNATURE_ALGORITHM="MD5withRSA";privatestaticfinalStringPUBLIC_KEY="RSAPublicKey";privatestaticfinalStringPRIVATE_KEY="RSAPrivateKey";/***用私钥对信息生成数字签名**@paramdata*加密数据*@paramprivateKey*私钥**@return*@throwsException*/publicstaticStringsign(byte[]data,StringprivateKey)throwsException{//解密由base64编码的私钥byte[]keyBytes=decryptBASE64(privateKey);//构造PKCS8EncodedKeySpec对象PKCS8EncodedKeySpecpkcs8KeySpec=newPKCS8EncodedKeySpec(keyBytes);//KEY_ALGORITHM指定的加密算法KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);//取私钥匙对象PrivateKeypriKey=keyFactory.generatePrivate(pkcs8KeySpec);//用私钥对信息生成数字签名Signaturesignature=Signature.getInstance(SIGNATURE_ALGORITHM);signature.initSign(priKey);signature.update(data);returnencryptBASE64(signature.sign());}/***校验数字签名**@paramdata*加密数据*@parampublicKey*公钥*@paramsign*数字签名**@return校验成功返回true失败返回false*@throwsException**/publicstaticbooleanverify(byte[]data,StringpublicKey,Stringsign)throwsException{//解密由base64编码的公钥byte[]keyBytes=decryptBASE64(publicKey);//构造X509EncodedKeySpec对象X509EncodedKeySpeckeySpec=newX509EncodedKeySpec(keyBytes);//KEY_ALGORITHM指定的加密算法KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);//取公钥匙对象PublicKeypubKey=keyFactory.generatePublic(keySpec);Signaturesignature=Signature.getInstance(SIGNATURE_ALGORITHM);signature.initVerify(pubKey);signature.update(data);//验证签名是否正常returnsignature.verify(decryptBASE64(sign));}/***解密<br>*用私钥解密**@paramdata*@paramkey*@return*@throwsException*/publicstaticbyte[]decryptByPrivateKey(byte[]data,Stringkey)throwsException{//对密钥解密byte[]keyBytes=decryptBASE64(key);//取得私钥PKCS8EncodedKeySpecpkcs8KeySpec=newPKCS8EncodedKeySpec(keyBytes);KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);KeyprivateKey=keyFactory.generatePrivate(pkcs8KeySpec);//对数据解密Ciphercipher=Cipher.getInstance(keyFactory.getAlgorithm());cipher.init(Cipher.DECRYPT_MODE,privateKey);returncipher.doFinal(data);}/***解密<br>*用公钥解密**@paramdata*@paramkey*@return*@throwsException*/publicstaticbyte[]decryptByPublicKey(byte[]data,Stringkey)throwsException{//对密钥解密byte[]keyBytes=decryptBASE64(key);//取得公钥X509EncodedKeySpecx509KeySpec=newX509EncodedKeySpec(keyBytes);KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);KeypublicKey=keyFactory.generatePublic(x509KeySpec);//对数据解密Ciphercipher=Cipher.getInstance(keyFactory.getAlgorithm());cipher.init(Cipher.DECRYPT_MODE,publicKey);returncipher.doFinal(data);}/***加密<br>*用公钥加密**@paramdata*@paramkey*@return*@throwsException*/publicstaticbyte[]encryptByPublicKey(byte[]data,Stringkey)throwsException{//对公钥解密byte[]keyBytes=decryptBASE64(key);//取得公钥X509EncodedKeySpecx509KeySpec=newX509EncodedKeySpec(keyBytes);KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);KeypublicKey=keyFactory.generatePublic(x509KeySpec);//对数据加密Ciphercipher=Cipher.getInstance(keyFactory.getAlgorithm());cipher.init(Cipher.ENCRYPT_MODE,publicKey);returncipher.doFinal(data);}/***加密<br>*用私钥加密**@paramdata*@paramkey*@return*@throwsException*/publicstaticbyte[]encryptByPrivateKey(byte[]data,Stringkey)throwsException{//对密钥解密byte[]keyBytes=decryptBASE64(key);//取得私钥PKCS8EncodedKeySpecpkcs8KeySpec=newPKCS8EncodedKeySpec(keyBytes);KeyFactorykeyFactory=KeyFactory.getInstance(KEY_ALGORITHM);KeyprivateKey=keyFactory.generatePrivate(pkcs8KeySpec);//对数据加密Ciphercipher=Cipher.getInstance(keyFactory.getAlgorithm());cipher.init(Cipher.ENCRYPT_MODE,privateKey);returncipher.doFinal(data);}/***取得私钥**@paramkeyMap*@return*@throwsException*/publicstaticStringgetPrivateKey(Map<String,Object>keyMap)throwsException{Keykey=(Key)keyMap.get(PRIVATE_KEY);returnencryptBASE64(key.getEncoded());}/***取得公钥**@paramkeyMap*@return*@throwsException*/publicstaticStringgetPublicKey(Map<String,Object>keyMap)throwsException{Keykey=(Key)keyMap.get(PUBLIC_KEY);returnencryptBASE64(key.getEncoded());}/***初始化密钥**@return*@throwsException*/publicstaticMap<String,Object>initKey()throwsException{KeyPairGeneratorkeyPairGen=KeyPairGenerator.getInstance(KEY_ALGORITHM);keyPairGen.initialize(1024);KeyPairkeyPair=keyPairGen.generateKeyPair();//公钥RSAPublicKeypublicKey=(RSAPublicKey)keyPair.getPublic();//私钥RSAPrivateKeyprivateKey=(RSAPrivateKey)keyPair.getPrivate();Map<String,Object>keyMap=newHashMap<String,Object>(2);keyMap.put(PUBLIC_KEY,publicKey);keyMap.put(PRIVATE_KEY,privateKey);returnkeyMap;}}
再给出一个测试类：
Java代码 importstaticorg.junit.Assert.*;importorg.junit.Before;importorg.junit.Test;importjava.util.Map;/****@author梁栋*@version1.0*@since1.0*/publicclassRSACoderTest{privateStringpublicKey;privateStringprivateKey;@BeforepublicvoidsetUp()throwsException{Map<String,Object>keyMap=RSACoder.initKey();publicKey=RSACoder.getPublicKey(keyMap);privateKey=RSACoder.getPrivateKey(keyMap);System.err.println("公钥:\n\r"+publicKey);System.err.println("私钥：\n\r"+privateKey);}@Testpublicvoidtest()throwsException{System.err.println("公钥加密——私钥解密");StringinputStr="abc";byte[]data=inputStr.getBytes();byte[]encodedData=RSACoder.encryptByPublicKey(data,publicKey);byte[]decodedData=RSACoder.decryptByPrivateKey(encodedData,privateKey);StringoutputStr=newString(decodedData);System.err.println("加密前:"+inputStr+"\n\r"+"解密后:"+outputStr);assertEquals(inputStr,outputStr);}@TestpublicvoidtestSign()throwsException{System.err.println("私钥加密——公钥解密");StringinputStr="sign";byte[]data=inputStr.getBytes();byte[]encodedData=RSACoder.encryptByPrivateKey(data,privateKey);byte[]decodedData=RSACoder.decryptByPublicKey(encodedData,publicKey);StringoutputStr=newString(decodedData);System.err.println("加密前:"+inputStr+"\n\r"+"解密后:"+outputStr);assertEquals(inputStr,outputStr);System.err.println("私钥签名——公钥验证签名");//产生签名Stringsign=RSACoder.sign(encodedData,privateKey);System.err.println("签名:\r"+sign);//验证签名booleanstatus=RSACoder.verify(encodedData,publicKey,sign);System.err.println("状态:\r"+status);assertTrue(status);}}
控制台输出：
Console代码 公钥:MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCYU/+I0+z1aBl5X6DUUOHQ7FZpmBSDbKTtx89JEcB64jFCkunELT8qiKly7fzEqD03g8ALlu5XvX+bBqHFy7YPJJP0ekE2X3wjUnh2NxlqpH3/B/xm1ZdSlCwDIkbijhBVDjA/bu5BObhZqQmDwIxlQInL9oVz+o6FbAZCyHBd7wIDAQAB私钥：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公钥加密——私钥解密加密前:abc解密后:abc公钥:MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDdOj40yEB48XqWxmPILmJAc7UecIN7F32etSHF9rwbuEh3+iTPOGSxhoSQpOED0vOb0ZIMkBXZSgsxLaBSin2RZ09YKWRjtpCA0kDkiD11gj4tzTiMl9qq1kwSK7ZkGAgodEn3yIILVmQDuEImHOXFtulvJ71ka07u3LuwUNdB/wIDAQAB私钥：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私钥加密——公钥解密加密前:sign解密后:sign私钥签名——公钥验证签名签名:ud1RsIwmSC1pN22I4IXteg1VD2FbiehKUfNxgVSHzvQNIK+d20FCkHCqh9djP3h94iWnIUY0ifU+mbJkhAl/i5krExOE0hknOnPMcEP+lZV1RbJI2zG2YooSp2XDleqrQk5e/QF2Mx0Zxt8Xsg7ucVpni3wwbYWs9wSzIf0UjlM=状态:true
简要总结一下，使用公钥加密、私钥解密，完成了乙方到甲方的一次数据传递，通过私钥加密、公钥解密，同时通过私钥签名、公钥验证签名，完成了一次甲方到乙方的数据传递与验证，两次数据传递完成一整套的数据交互！
类似数字签名，数字信封是这样描述的：
数字信封
数字信封用加密技术来保证只有特定的收信人才能阅读信的内容。
流程：
信息发送方采用对称密钥来加密信息，然后再用接收方的公钥来加密此对称密钥（这部分称为数字信封），再将它和信息一起发送给接收方；接收方先用相应的私钥打开数字信封，得到对称密钥，然后使用对称密钥再解开信息。
