RSA通俗理解：
你只要去想：既然是加密，那肯定是不希望别人知道我的消息，所以只有我才能解密，所以可得出公钥负责加密，私钥负责解密；同理，既然是签名，那肯定是不希望有人冒充我发消息，只有我才能发布这个签名，所以可得出私钥负责签名，公钥负责验证。
实现代码：
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package com.sahadev;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import javax.crypto.Cipher;
import org.apache.commons.codec.binary.Base64;
public class RSA {
public static void main(String[] args) {
JDKRSA();
}
public static void JDKRSA() {
try {
// 构建密钥对儿
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(512);
KeyPair keyPair = keyPairGenerator.generateKeyPair();
RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();
RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();
System.out.println("Public Key : " + org.apache.commons.codec.binary.Base64.encodeBase64String(rsaPublicKey.getEncoded()));
System.out.println("Private Key : " + org.apache.commons.codec.binary.Base64.encodeBase64String(rsaPrivateKey.getEncoded()));
// 2.私钥加密，公钥解密---加密
PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
byte[] result = cipher.doFinal(DH.src.getBytes());
System.out.println("私钥加密，公钥解密------加密 : " + Base64.encodeBase64String(result));
// 3.私钥加密，公钥解密---解密
X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(rsaPublicKey.getEncoded());
keyFactory = KeyFactory.getInstance("RSA");
PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, publicKey);
result = cipher.doFinal(result);
System.out.println("私钥加密，公钥解密------解密 : " + new String(result));
// 4.公钥加密，私钥解密---加密
x509EncodedKeySpec = new X509EncodedKeySpec(rsaPublicKey.getEncoded());
keyFactory = KeyFactory.getInstance("RSA");
publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
result = cipher.doFinal(DH.src.getBytes());
System.out.println("公钥加密，私钥解密------加密 : " + Base64.encodeBase64String(result));
// 5.公钥加密，私钥解密---解密
pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());
keyFactory = KeyFactory.getInstance("RSA");
privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
result = cipher.doFinal(result);
System.out.println("公钥加密，私钥解密------解密 : " + new String(result));
} catch (Exception e) {
e.printStackTrace();
}
}
}
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附上输出结果：
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Public Key : MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAJcFshoP5xm94r2aTbe++aMZMzJtXHxDpqmMQ9aL1cEthr2Xtac+Eckv32Kzb4R8C/6vObNBfd8sWx9FU5N2y6cCAwEAAQ==
Private Key : MIIBVAIBADANBgkqhkiG9w0BAQEFAASCAT4wggE6AgEAAkEAlwWyGg/nGb3ivZpNt775oxkzMm1cfEOmqYxD1ovVwS2GvZe1pz4RyS/fYrNvhHwL/q85s0F93yxbH0VTk3bLpwIDAQABAkBdAA7rabug6IRGykztyFcmjxAuD5aSl358jnoAFuCtMo4skfxh1vR4ENFUE0Lt0zJ3CKVH0o9UQDNG0r4jeOGRAiEA3KuXps9OG0AXuxLggg0e7B1Os5C3gNrH2fMqAPjtpY0CIQCvM4EPfdrjjNQiM0ATVBT5jZnw3PRu33pdyISWuoMHAwIgDOLMSUZjxj2Y5Si2CYIgoyMW/G9f99tOvlBvzHy8y+UCIF94MVu/uQdGNlJsmv3tU4CpKLmXrZq9LHDuU1HPUJcBAiEAy/0OS2Q9EBfmPwhsGXF4WMxj4wG0xzNFWxSeZB0qxzk=
私钥加密，公钥解密------加密 : NXF87irBEmK3x/fW7IWY4GuA8AP4Rvj4DJSp2Cjjsoo5X/ScHHKdvYtlM+9TOUAvMeuKWk5WH70g53q7+E73zg==
私钥加密，公钥解密------解密 : Hello,sahadev!
公钥加密，私钥解密------加密 : hjL8928jCbNtVCRhKaYAxQNJmiIAktBskhff2I01pbaHtfGH6GJTcP1i345/3I9OzwoVFxvi/oXgVJsIsg7MOQ==
公钥加密，私钥解密------解密 : Hello,sahadev!
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原文链接：http://blog.csdn.net/sahadev_/article/details/48796057