本文完成的是公钥加密，私钥解密（私钥加密公钥解密是一样的）。
注意点：
秘钥生成的格式不同，使用算法也不同，公钥是X509EncodedKeySpec，私钥是PKCS8EncodedKeySpec。报错java.security.spec.InvalidKeySpecException就是因为密钥格式问题。报错Data must not be longer than *** bytes是因为没有分段解密，密文太长。分段加密解密时钥注意偏移量，256位或者128位钥看自己密钥的生成。本文把公私密钥做了编码获取处理是为了方便传输，如果不需要传输，可以不做，代码稍改即可。
代码如下
package RSA;import javax.crypto.BadPaddingException;import javax.crypto.Cipher;import javax.crypto.IllegalBlockSizeException;import javax.crypto.NoSuchPaddingException;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.UnsupportedEncodingException;import java.security.*;import java.security.spec.InvalidKeySpecException;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.X509EncodedKeySpec;import java.util.Base64;/*** @version v1.0* @ProjectName: Cryptography* @ClassName: RSA* @Description: TODO(RSA加密解密算法类)* @Author: 你还年轻* @Date: /9/27 21:04*/public class RSA {/*** @Description: TODO(获取密钥对)* @param * @return {@link KeyPair}* @author 你还年轻* @throws* @date /9/27 21:48*/public static KeyPair generateKeyPairs() throws NoSuchAlgorithmException, UnsupportedEncodingException {//标明算法类型String algorithm = "RSA";//创建秘钥对生成对象(密钥生成器)KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(algorithm);SecureRandom secureRandom = new SecureRandom(String.valueOf(System.currentTimeMillis()).getBytes("utf-8")); // 说的一个安全的随机数keyPairGenerator.initialize(2048, secureRandom); // 这里可以是1024、2048 初始化一个密钥对//生成密钥对，此时公钥好私钥已经在keyPair对象中KeyPair keyPair = keyPairGenerator.generateKeyPair();return keyPair;}/*** @Description: TODO(获取密钥对中的公钥，并对其进行Base64编码处理)* @param keyPair* @return {@link String}* @author 你还年轻* @throws* @date /9/27 21:49*/public static String getPublicKeyBase64(KeyPair keyPair){//获取传进来的密钥对中的公钥PublicKey publicKey = keyPair.getPublic();//对公钥进行Base64编码String publicKeyBase64 = Base64.getEncoder().encodeToString(publicKey.getEncoded());return publicKeyBase64;}/*** @Description: TODO(获取密钥对中的私钥，并对其进行Base64编码处理)* @param keyPair* @return {@link String}* @author 你还年轻* @throws* @date /9/27 22:43*/public static String getPrivateKeyBase64(KeyPair keyPair){//获取传进来的密钥对中的私钥PrivateKey privateKey = keyPair.getPrivate();//对私钥进行Base64编码处理String privateKeyBase64 = Base64.getEncoder().encodeToString(privateKey.getEncoded());return privateKeyBase64;}/*** @Description: TODO(使用公钥加密)* @param publicKeyStr 经过Base64编码过的公钥字符串* @param content* @return {@link String}* @author 你还年轻* @throws* @date /9/27 23:12*/public static String publicKeyEncrypt(String content,String publicKeyStr)throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, NoSuchProviderException, IOException {// 传递进来的公钥是经过Base64编码过的字符串，要返回成字节数组形式，需要解码byte[] decodePublicKeyByte = Base64.getDecoder().decode(publicKeyStr);//调用X509EncodedKeySpec对象,转换格式X509EncodedKeySpec keySpec = new X509EncodedKeySpec(decodePublicKeyByte);//调用密钥工厂KeyFactory keyFactory = KeyFactory.getInstance("RSA");PublicKey publicKey = keyFactory.generatePublic(keySpec);//调用Java加密的Cipher对象，Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.ENCRYPT_MODE,publicKey);//第一个参数表示这是加密模式，第二个参数表示密钥//分段加密byte[] bytesContent = content.getBytes();int inputLen = bytesContent.length;int offLen = 0;//偏移量int i = 0;ByteArrayOutputStream bops = new ByteArrayOutputStream();while(inputLen - offLen > 0){byte [] cache;if(inputLen - offLen > 256){cache = cipher.doFinal(bytesContent, offLen,256);}else{cache = cipher.doFinal(bytesContent, offLen,inputLen - offLen);}bops.write(cache);i++;offLen = 256 * i;}bops.close();byte[] encryptedData = bops.toByteArray();//使用Base64对加密结果进行编码String encode = Base64.getEncoder().encodeToString(encryptedData);return new String(encode);}/*** @Description: TODO(私钥解密)* @param content 秘文，base64编码过的字符串* @param privateKeyStr 私钥，base64编码过的字符串* @return {@link String}* @author 你还年轻* @throws* @date /9/27 23:15*/public static String privateKeyDecrypt(String content,String privateKeyStr)throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, BadPaddingException, IllegalBlockSizeException, InvalidKeyException, IOException {//传递进来的私钥是经过Base64编码过的字符串，要返回成字节数组形式，需要解码byte[] decodePrivateKeyByte = Base64.getDecoder().decode(privateKeyStr);//调用PKCS8EncodedKeySpec对象PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(decodePrivateKeyByte);//调用密钥工厂KeyFactory keyFactory = KeyFactory.getInstance("RSA");PrivateKey privateKey = keyFactory.generatePrivate(keySpec);//调用Java加密的Cipher对象，Cipher cipher = Cipher.getInstance("RSA");cipher.init(Cipher.DECRYPT_MODE,privateKey);//第一个参数表示这是加密模式，第二个参数表示密钥byte[] bytesContent = Base64.getDecoder().decode(content.getBytes());int inputLen = bytesContent.length;int offLen = 0;int i = 0;ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();while(inputLen - offLen > 0){byte[] cache;if(inputLen - offLen > 256){cache = cipher.doFinal(bytesContent,offLen,256);}else{cache = cipher.doFinal(bytesContent,offLen,inputLen - offLen);}byteArrayOutputStream.write(cache);i++;offLen = 256 * i;}byteArrayOutputStream.close();byte[] byteArray = byteArrayOutputStream.toByteArray();//使用Base64对加密结果进行编码return new String(byteArray);}public static void main(String[] args) throwsNoSuchAlgorithmException, IllegalBlockSizeException, InvalidKeyException, BadPaddingException, InvalidKeySpecException, NoSuchPaddingException, IOException, NoSuchProviderException {String input = "123321";KeyPair keyPair = generateKeyPairs();String en = publicKeyEncrypt(input,getPublicKeyBase64(keyPair));String de = privateKeyDecrypt(en, getPrivateKeyBase64(keyPair));System.out.println("原文："+input);System.out.println("密文："+ en);System.out.println("解密："+de);}}
测试
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