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import javax.crypto.Cipher;import java.security.*;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.X509EncodedKeySpec;import java.util.Base64;
public class RSAKeyPair { // 私钥: PrivateKey sk; // 公钥: PublicKey pk;
 // 生成公钥/私钥对: public RSAKeyPair() throws GeneralSecurityException { KeyPairGenerator kpGen = KeyPairGenerator.getInstance("RSA"); kpGen.initialize(1024); KeyPair kp = kpGen.generateKeyPair(); this.sk = kp.getPrivate(); this.pk = kp.getPublic(); }
 // 从已保存的字节中（例如：读取文件）恢复公钥/私钥: public RSAKeyPair(byte[] pk, byte[] sk) throws GeneralSecurityException{ KeyFactory kf = KeyFactory.getInstance("RSA"); X509EncodedKeySpec pkSpec = new X509EncodedKeySpec(pk); this.pk = kf.generatePublic(pkSpec); PKCS8EncodedKeySpec skSpec = new PKCS8EncodedKeySpec(sk); this.sk = kf.generatePrivate(skSpec); }
 // 把私钥导出为字节 public byte[] getPrivateKey(){ return this.sk.getEncoded(); }
 // 把公钥导出为字节 public byte[] getPublicKey(){ return this.pk.getEncoded(); }
 // 用公钥加密: public byte[] encrypt(byte[] message) throws GeneralSecurityException{ Cipher cipher = Cipher.getInstance("RSA"); cipher.init(Cipher.ENCRYPT_MODE, this.pk); return cipher.doFinal(message); }
 // 用私钥解密: public byte[] decrypt(byte[] input) throws GeneralSecurityException{ Cipher cipher = Cipher.getInstance("RSA"); cipher.init(Cipher.DECRYPT_MODE, this.sk); return cipher.doFinal(input); }
 public static void main(String[] args) throws Exception{ // 明文： byte[] plain = "Hello，使用RSA非对称加密算法对数据进行加密！".getBytes(); // 创建公钥/私钥对： RSAKeyPair rsa = new RSAKeyPair(); // 加密： byte[] encrypted = rsa.encrypt(plain); System.out.println("encrypted: " + Base64.getEncoder().encodeToString(encrypted)); // 解密： byte[] decrypted = rsa.decrypt(encrypted); System.out.println("decrypted: " + new String(decrypted, "UTF-8")); // 保存公钥/私钥： byte[] pk = rsa.getPublicKey(); byte[] sk = rsa.getPrivateKey(); System.out.println("pk: " + Base64.getEncoder().encodeToString(pk)); System.out.println("sk: " + Base64.getEncoder().encodeToString(sk)); // 重新恢复公钥/私钥： RSAKeyPair rsa2 = new RSAKeyPair(pk, sk); // 加密： byte[] encrypted2 = rsa2.encrypt(plain); System.out.println("encrypted: " + Base64.getEncoder().encodeToString(encrypted2)); // 解密： byte[] decrypted2 = rsa2.decrypt(encrypted2); System.out.println("decrypted: " + new String(decrypted2, "UTF-8")); }}