Java 实现RSA非对称加密算法

公钥与私钥是成对的，一般的，我们认为的是公钥加密、私钥解密、私钥签名、公钥验证，有人说成私钥加密，公钥解密时不对的。

公钥与私钥的生成有多种方式，可以通过程序生成（下文具体实现），可以通过openssl工具：

# 生成一个私钥，推荐使用1024位的秘钥，秘钥以pem格式保存到-out参数指定的文件中，采用PKCS1格式 openssl genrsa -out rsa.pem 1024 # 生成与私钥对应的公钥，生成的是Subject Public Key，一般配合PKCS8格式私钥使用 openssl rsa -in rsa.pem -pubout -out rsa.pub

RSA生成公钥与私钥一般有两种格式：PKCS1和PKCS8，上面的命令生成的秘钥是PKCS1格式的，而公钥是Subject Public Key，一般配合PKCS8格式私钥使用，所以就可能会涉及到PKCS1和PKCS8之间的转换：

# PKCS1格式私钥转换为PKCS8格式私钥，私钥直接输出到-out参数指定的文件中 openssl pkcs8 -topk8 -inform PEM -in rsa.pem -outform pem -nocrypt -out rsa_pkcs8.pem # PKCS8格式私钥转换为PKCS1格式私钥，私钥直接输出到-out参数指定的文件中 openssl rsa -in rsa_pkcs8.pem -out rsa_pkcs1.pem # PKCS1格式公钥转换为PKCS8格式公钥，转换后的内容直接输出 openssl rsa -pubin -in rsa.pub -RSAPublicKey_out # PKCS8格式公钥转换为PKCS1格式公钥，转换后的内容直接输出 openssl rsa -RSAPublicKey_in -pubout -in rsa.pub

现实中，我们往往从pem、crt、pfx文件获取公私和私钥，crt、pfx的制作可以参考：简单的制作ssl证书，并在nginx和IIS中使用，或者使用现成的：https://pan.baidu.com/s/1MJ5YmuZiLBnf-DfNR_6D7A (提取码：c6tj)，密码都是：123456

为简化说明介绍，这里我直接封装了一个工具类，因为要从pem、crt、pfx文件获取公私和私钥，因此引用了一个第三方包：BouncyCastle，可以直接在pom.xml中添加依赖：

<dependency><groupId>org.bouncycastle</groupId><artifactId>bcprov-jdk15on</artifactId><version>1.68</version> </dependency>

或者去mvn上下载：跳转

简单封装的RsaUtil.java:

import java.io.FileInputStream;import java.io.FileReader;import java.io.FileWriter;import java.math.BigInteger;import java.security.KeyFactory;import java.security.KeyPair;import java.security.KeyPairGenerator;import java.security.KeyStore;import java.security.PrivateKey;import java.security.PublicKey;import java.security.SecureRandom;import java.security.Security;import java.security.Signature;import java.security.cert.Certificate;import java.security.cert.CertificateFactory;import java.security.cert.X509Certificate;import java.security.interfaces.RSAPrivateKey;import java.security.interfaces.RSAPublicKey;import java.security.spec.KeySpec;import java.security.spec.PKCS8EncodedKeySpec;import java.security.spec.RSAPrivateCrtKeySpec;import java.security.spec.RSAPublicKeySpec;import java.security.spec.X509EncodedKeySpec;import java.util.Enumeration;import javax.crypto.Cipher;import org.bouncycastle.asn1.ASN1Integer;import org.bouncycastle.asn1.ASN1Primitive;import org.bouncycastle.asn1.DLSequence;import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;import org.bouncycastle.asn1.x509.AlgorithmIdentifier;import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;import org.bouncycastle.jce.provider.BouncyCastleProvider;import org.bouncycastle.util.io.pem.PemObject;import org.bouncycastle.util.io.pem.PemReader;import org.bouncycastle.util.io.pem.PemWriter;public class RsaUtil { static {Security.addProvider(new BouncyCastleProvider()); } /** * 随机生成密钥对 * * @param usePKCS8 * 是否采用PKCS8填充模式 */ public static Object[] generateRsaKey(boolean usePKCS8) throws Exception {KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance('RSA', BouncyCastleProvider.PROVIDER_NAME);// 初始化keyPairGen.initialize(1024, new SecureRandom());// 生成一个密钥对，保存在keyPair中KeyPair keyPair = keyPairGen.generateKeyPair();RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate(); // 得到私钥RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic(); // 得到公钥// 这两个公私钥是PKCS8格式的byte[] publicKeyBytes = publicKey.getEncoded();byte[] privateKeyBytes = privateKey.getEncoded();if (!usePKCS8) { // 将PSCK8格式公私钥转换为PKCS1格式 publicKeyBytes = pkcs8ToPkcs1(false, publicKeyBytes); privateKeyBytes = pkcs8ToPkcs1(true, privateKeyBytes);}return new Object[] { publicKeyBytes, privateKeyBytes }; } /** * 从Pem文件读取密钥对 * * @param reader * 输入流 * @param pemFileName * pem文件 */ public static byte[] readFromPem(String pemFileName) throws Exception {PemReader pemReader = new PemReader(new FileReader(pemFileName));PemObject pemObject = pemReader.readPemObject();byte[] publicKey = pemObject.getContent();pemReader.close();return publicKey; } /** * 从Pem文件读取密钥 * * @param isPrivateKey * 是否是私钥 * @param buffer * 字节 * @param pemFileName * pem文件 */ public static void writeToPem(byte[] buffer, boolean isPrivateKey, String pemFileName) throws Exception {PemObject pemObject = new PemObject(isPrivateKey ? 'RSA PRIVATE KEY' : 'RSA PUBLIC KEY', buffer);FileWriter fileWriter = new FileWriter(pemFileName);PemWriter pemWriter = new PemWriter(fileWriter);pemWriter.writeObject(pemObject);pemWriter.close(); } /** * 从crt文件读取公钥(pkcs8) * * @param crtFileName * crt文件 * @return 公钥 */ public static byte[] readPublicKeyFromCrt(String crtFileName) throws Exception {CertificateFactory cf = CertificateFactory.getInstance('X.509');X509Certificate cert = (X509Certificate) cf.generateCertificate(new FileInputStream(crtFileName));PublicKey publicKey = cert.getPublicKey();return publicKey.getEncoded(); } /** * 从pfx文件读取秘钥对(pkcs8) * * @param pfxFileName * pfx文件 * @return 秘钥对 */ public static Object[] readFromPfx(String pfxFileName, String password) throws Exception {KeyStore keystore = KeyStore.getInstance('PKCS12');char[] passwordChars = null;if (password == null || password.equals('')) { passwordChars = null;} else { passwordChars = password.toCharArray();}keystore.load(new FileInputStream(pfxFileName), passwordChars);Enumeration<String> enums = keystore.aliases();PrivateKey privateKey = null;Certificate certificate = null;while (enums.hasMoreElements()) { String alias = enums.nextElement(); System.out.println(alias); if (keystore.isKeyEntry(alias)) {privateKey = (PrivateKey) keystore.getKey(alias, passwordChars);certificate = keystore.getCertificate(alias); } if (privateKey != null && certificate != null)break;}if (privateKey == null || certificate == null) { throw new Exception('fail to read key from pfx');}PublicKey publicKey = certificate.getPublicKey();return new Object[] { publicKey.getEncoded(), privateKey.getEncoded() }; } /** * Pkcs8转Pkcs1 * * @param isPrivateKey * 是否是私钥转换 * @param buffer * Pkcs1秘钥 * @return Pkcs8秘钥 * @throws Exception * 加密过程中的异常信息 */ public static byte[] pkcs8ToPkcs1(boolean isPrivateKey, byte[] buffer) throws Exception {if (isPrivateKey) { PrivateKeyInfo privateKeyInfo = PrivateKeyInfo.getInstance(buffer); return privateKeyInfo.parsePrivateKey().toASN1Primitive().getEncoded();} else { SubjectPublicKeyInfo subjectPublicKeyInfo = SubjectPublicKeyInfo.getInstance(buffer); return subjectPublicKeyInfo.parsePublicKey().toASN1Primitive().getEncoded();} } /** * Pkcs1转Pkcs8 * * @param isPrivateKey * 是否是私钥转换 * @param buffer * Pkcs1秘钥 * @return Pkcs8秘钥 * @throws Exception * 加密过程中的异常信息 */ public static byte[] pkcs1ToPkcs8(boolean isPrivateKey, byte[] buffer) throws Exception {AlgorithmIdentifier algorithmIdentifier = new AlgorithmIdentifier(PKCSObjectIdentifiers.rsaEncryption);ASN1Primitive asn1Primitive = ASN1Primitive.fromByteArray(buffer);if (isPrivateKey) { PrivateKeyInfo privateKeyInfo = new PrivateKeyInfo(algorithmIdentifier, asn1Primitive); return privateKeyInfo.getEncoded();} else { SubjectPublicKeyInfo subjectPublicKeyInfo = new SubjectPublicKeyInfo(algorithmIdentifier, asn1Primitive); return subjectPublicKeyInfo.getEncoded();} } /** * RSA公钥 * * @param usePKCS8 * 是否采用PKCS8填充模式 * @param publicKey * 公钥 * @return 公钥 * @throws Exception * 加密过程中的异常信息 */ public static RSAPublicKey generatePublicKey(boolean usePKCS8, byte[] publicKey) throws Exception {KeySpec keySpec;if (usePKCS8) { // PKCS8填充 keySpec = new X509EncodedKeySpec(publicKey);} else { // PKCS1填充 DLSequence sequence = (DLSequence) ASN1Primitive.fromByteArray(publicKey); BigInteger v1 = ((ASN1Integer) sequence.getObjectAt(0)).getValue(); BigInteger v2 = ((ASN1Integer) sequence.getObjectAt(1)).getValue(); keySpec = new RSAPublicKeySpec(v1, v2);}RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance('RSA', BouncyCastleProvider.PROVIDER_NAME).generatePublic(keySpec);return pubKey; } /** * RSA私钥 * * @param usePKCS8 * 是否采用PKCS8填充模式 * @param privateKey * 私钥 * @return 私钥 * @throws Exception * 解密过程中的异常信息 */ public static RSAPrivateKey generatePrivateKey(boolean usePKCS8, byte[] privateKey) throws Exception {KeySpec keySpec;if (usePKCS8) { // PKCS8填充 keySpec = new PKCS8EncodedKeySpec(privateKey);} else { // PKCS1填充 DLSequence sequence = (DLSequence) ASN1Primitive.fromByteArray(privateKey); // BigInteger v1= ((ASN1Integer)sequence.getObjectAt(0)).getValue(); BigInteger v2 = ((ASN1Integer) sequence.getObjectAt(1)).getValue(); BigInteger v3 = ((ASN1Integer) sequence.getObjectAt(2)).getValue(); BigInteger v4 = ((ASN1Integer) sequence.getObjectAt(3)).getValue(); BigInteger v5 = ((ASN1Integer) sequence.getObjectAt(4)).getValue(); BigInteger v6 = ((ASN1Integer) sequence.getObjectAt(5)).getValue(); BigInteger v7 = ((ASN1Integer) sequence.getObjectAt(6)).getValue(); BigInteger v8 = ((ASN1Integer) sequence.getObjectAt(7)).getValue(); BigInteger v9 = ((ASN1Integer) sequence.getObjectAt(8)).getValue(); keySpec = new RSAPrivateCrtKeySpec(v2, v3, v4, v5, v6, v7, v8, v9);}RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance('RSA', BouncyCastleProvider.PROVIDER_NAME).generatePrivate(keySpec);return priKey; } /** * RSA公钥加密 * * @param value * 加密字符串 * @param publicKey * 公钥 * @return 密文 * @throws Exception * 加密过程中的异常信息 */ public static String rsaEncrypt(String value, RSAPublicKey publicKey) throws Exception {if (value == null || value.length() == 0) return '';// RSA加密Cipher cipher = Cipher.getInstance('RSA');cipher.init(Cipher.ENCRYPT_MODE, publicKey);byte[] buffer = cipher.doFinal(value.getBytes('utf-8'));// 使用hex格式输出公钥StringBuffer result = new StringBuffer();for (int i = 0; i < buffer.length; i++) { result.append(String.format('%02x', buffer[i]));}return result.toString(); } /** * RSA私钥解密 * * @param value * 加密字符串 * @param privateKey * 私钥 * @return 明文 * @throws Exception * 解密过程中的异常信息 */ public static String rsaDecrypt(String value, RSAPrivateKey privateKey) throws Exception {if (value == null || value.length() == 0) return '';byte[] buffer = new byte[value.length() / 2];for (int i = 0; i < buffer.length; i++) { buffer[i] = (byte) Integer.parseInt(value.substring(i * 2, i * 2 + 2), 16);}// RSA解密Cipher cipher = Cipher.getInstance('RSA');cipher.init(Cipher.DECRYPT_MODE, privateKey);buffer = cipher.doFinal(buffer);return new String(buffer, 'utf-8'); } /** * RSA签名 * * @param value * 加密字符串 * @param privateKey * 私钥 * @param halg * 加密算法，如MD5, SHA1, SHA256, SHA384, SHA512等 * @return 签名 * @throws Exception * 签名过程中的异常信息 */ public static String sign(String value, RSAPrivateKey privateKey, String halg) throws Exception {Signature s = Signature.getInstance(halg.toUpperCase().endsWith('WithRSA') ? halg : (halg + 'WithRSA'));s.initSign(privateKey);s.update(value.getBytes('utf-8'));byte[] buffer = s.sign();// 使用hex格式输出公钥StringBuffer result = new StringBuffer();for (int i = 0; i < buffer.length; i++) { result.append(String.format('%02x', buffer[i]));}return result.toString(); } /** * RSA签名验证 * * @param value * 加密字符串 * @param publicKey * 公钥 * @param halg * 加密算法，如MD5, SHA1, SHA256, SHA384, SHA512等 * @return 签名合法则返回true，否则返回false * @throws Exception * 验证过程中的异常信息 */ public static boolean verify(String value, RSAPublicKey publicKey, String signature, String halg) throws Exception {Signature s = Signature.getInstance(halg.toUpperCase().endsWith('WithRSA') ? halg : (halg + 'WithRSA'));s.initVerify(publicKey);s.update(value.getBytes('utf-8'));byte[] buffer = new byte[signature.length() / 2];for (int i = 0; i < buffer.length; i++) { buffer[i] = (byte) Integer.parseInt(signature.substring(i * 2, i * 2 + 2), 16);}return s.verify(buffer); }}

　生成公钥和私钥：

// 生成公私钥 Object[] rsaKey = RsaUtil.generateRsaKey(usePKCS8); //usePKCS8=true表示是否成PKCS8格式的公私秘钥,否则乘车PKCS1格式的公私秘钥 byte[] publicKey = (byte[]) rsaKey[0]; byte[] privateKey = (byte[]) rsaKey[1];

生成秘钥后，需要保存，一般保存到pem文件中：　

// 保存到pem文件，filePath是保存目录 RsaUtil.writeToPem(publicKey, false, filePath + 'rsa.pub'); RsaUtil.writeToPem(privateKey, true, filePath + 'rsa.pem');

　可以保存到pem文件中，当然也可以从pem文件中读取了：

// 从Pem文件读取公私钥，filePath是文件目录 byte[] publicKey = RsaUtil.readFromPem(filePath + 'rsa.pub'); byte[] privateKey = RsaUtil.readFromPem(filePath + 'rsa.pem');

还可以从crt证书中读取公钥，而crt文件不包含私钥，因此需要单独获取私钥：　

// 从crt文件读取公钥（crt文件中不包含私钥），filePath是文件目录 byte[] publicKey = RsaUtil.readPublicKeyFromCrt(filePath + 'demo.crt'); byte[] privateKey = RsaUtil.readFromPem(filePath + 'demo.key');

　pfx文件中包含了公钥和私钥，可以很方便就读取到：

// 从pfx文件读取公私钥，filePath是文件目录 Object[] rsaKey = RsaUtil.readFromPfx(filePath + 'demo.pfx', '123456'); byte[] publicKey = (byte[]) rsaKey[0]; byte[] privateKey = (byte[]) rsaKey[1];

有时候我们还可能需要进行秘钥的转换：

// Pkcs8格式公钥转换为Pkcs1格式公钥 publicKey = RsaUtil.pkcs8ToPkcs1(false, publicKey); // Pkcs8格式私钥转换为Pkcs1格式私钥 privateKey = RsaUtil.pkcs8ToPkcs1(true, privateKey); // Pkcs1格式公钥转换为Pkcs8格式公钥 publicKey = RsaUtil.pkcs1ToPkcs8(false, publicKey); // Pkcs1格式私钥转换为Pkcs8格式私钥 privateKey = RsaUtil.pkcs1ToPkcs8(true, privateKey);

有了公钥和私钥，接下就就能实现加密、解密、签名、验证签名等操作了：

RSAPublicKey rsaPublicKey = RsaUtil.generatePublicKey(usePKCS8, publicKey); RSAPrivateKey rsaPrivateKey = RsaUtil.generatePrivateKey(usePKCS8, privateKey); String encryptText = RsaUtil.rsaEncrypt(text, rsaPublicKey); System.out.printf('【%s】经过【RSA】加密后：%sn', text, encryptText); String decryptText = RsaUtil.rsaDecrypt(encryptText, rsaPrivateKey); System.out.printf('【%s】经过【RSA】解密后：%sn', encryptText, decryptText); String signature = RsaUtil.sign(text, rsaPrivateKey, 'MD5'); System.out.printf('【%s】经过【RSA】签名后：%sn', text, signature); boolean result = RsaUtil.verify(text, rsaPublicKey, signature, 'MD5'); System.out.printf('【%s】的签名【%s】经过【RSA】验证后结果是：' + result, text, signature);

这里完整的demo代码：

import java.security.interfaces.RSAPrivateKey; import java.security.interfaces.RSAPublicKey;public class RsaMain { public static void main(String[] args) { try {String text = '上山打老虎';boolean usePKCS8 = true; // usePKCS8=true表示是否成PKCS8格式的公私秘钥,否则乘车PKCS1格式的公私秘钥String filePath = RsaUtil.class.getClassLoader().getResource('').getPath();System.out.printf('文件路径：%sn', filePath);// 存放pem,crt,pfx等文件的目录byte[] publicKey, privateKey;// 公钥和私钥 // 生成公私钥Object[] rsaKey = RsaUtil.generateRsaKey(usePKCS8); // usePKCS8=true表示是否成PKCS8格式的公私秘钥,否则乘车PKCS1格式的公私秘钥publicKey = (byte[]) rsaKey[0];privateKey = (byte[]) rsaKey[1];// 从Pem文件读取公私钥，filePath是文件目录// publicKey = RsaUtil.readFromPem(filePath + 'rsa.pub');// privateKey = RsaUtil.readFromPem(filePath + 'rsa.pem');// 从pfx文件读取公私钥，filePath是文件目录// Object[] rsaKey = RsaUtil.readFromPfx(filePath + 'demo.pfx',// '123456');// publicKey = (byte[]) rsaKey[0];// privateKey = (byte[]) rsaKey[1];// 从crt文件读取公钥（crt文件中不包含私钥），filePath是文件目录// publicKey = RsaUtil.readPublicKeyFromCrt(filePath + 'demo.crt');// privateKey = RsaUtil.readFromPem(filePath + 'demo.key'); // 保存到pem文件，filePath是保存目录RsaUtil.writeToPem(publicKey, false, filePath + 'rsa.pub');RsaUtil.writeToPem(privateKey, true, filePath + 'rsa.pem'); // Pkcs8格式公钥转换为Pkcs1格式公钥publicKey = RsaUtil.pkcs8ToPkcs1(false, publicKey);// Pkcs8格式私钥转换为Pkcs1格式私钥privateKey = RsaUtil.pkcs8ToPkcs1(true, privateKey);// Pkcs1格式公钥转换为Pkcs8格式公钥publicKey = RsaUtil.pkcs1ToPkcs8(false, publicKey);// Pkcs1格式私钥转换为Pkcs8格式私钥privateKey = RsaUtil.pkcs1ToPkcs8(true, privateKey); RSAPublicKey rsaPublicKey = RsaUtil.generatePublicKey(usePKCS8, publicKey);RSAPrivateKey rsaPrivateKey = RsaUtil.generatePrivateKey(usePKCS8, privateKey); String encryptText = RsaUtil.rsaEncrypt(text, rsaPublicKey);System.out.printf('【%s】经过【RSA】加密后：%sn', text, encryptText); String decryptText = RsaUtil.rsaDecrypt(encryptText, rsaPrivateKey);System.out.printf('【%s】经过【RSA】解密后：%sn', encryptText, decryptText); String signature = RsaUtil.sign(text, rsaPrivateKey, 'MD5');System.out.printf('【%s】经过【RSA】签名后：%sn', text, signature); boolean result = RsaUtil.verify(text, rsaPublicKey, signature, 'MD5');System.out.printf('【%s】的签名【%s】经过【RSA】验证后结果是：' + result, text, signature);} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace(); }} }

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