简介
对称加解密算法都需要一把秘钥，但是很多情况下，互联网环境不适合传输这把对称密码，有密钥泄露的风险，为了解决这个问题ECDH密钥交换应运而生
EC：Elliptic Curve——椭圆曲线，生成密钥的方法
DH：Diffie-Hellman Key Exchange——交换密钥的方法
设计
数据传输的两方服务端（Server）和客户端（Client）
服务端生成密钥对Server-Public和Servier-Private
客户端生成密钥对Client-Public和Client-Private
客户端获取服务端的公钥和客户端的私钥进行计算CaculateKey(Server-Public，Client-Private)出共享密钥ShareKey1
服务端获取客户端的公钥和服务端的私钥进行计算CaculateKey(Client-Public，Server-Private)出共享密钥ShareKey2
ShareKey1和ShareKey2必定一致，ShareKey就是双方传输数据进行AES加密时的密钥
实现
生成密钥对
后端
public static ECDHKeyInfo generateKeyInfo(){
ECDHKeyInfo keyInfo = new ECDHKeyInfo();
try{
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("EC");
ECGenParameterSpec ecSpec = new ECGenParameterSpec("secp256r1");
keyPairGenerator.initialize(ecSpec, new SecureRandom());
KeyPair kp = keyPairGenerator.generateKeyPair();
ECPublicKey ecPublicKey = (ECPublicKey) kp.getPublic();
ECPrivateKey ecPrivateKey = (ECPrivateKey) kp.getPrivate();
// 获取公钥点的x和y坐标
BigInteger x = ecPublicKey.getW().getAffineX();
BigInteger y = ecPublicKey.getW().getAffineY();
// 将x和y坐标转换为十六进制字符串
String xHex = x.toString(16);
String yHex = y.toString(16);
String publicKey = xHex + "|" + yHex;
String privateKey = Base64.getEncoder().encodeToString(ecPrivateKey.getEncoded());
keyInfo.setPublicKey(publicKey);
keyInfo.setPrivateKey(privateKey);
}catch (Exception e){
e.printStackTrace();
}
return keyInfo;
}
public static class ECDHKeyInfo{
private String publicKey;
private String privateKey;
public String getPublicKey() {
return publicKey;
}
public void setPublicKey(String publicKey) {
this.publicKey = publicKey;
}
public String getPrivateKey() {
return privateKey;
}
public void setPrivateKey(String privateKey) {
this.privateKey = privateKey;
}
}
前端
引入elliptic.js（https://cdn.bootcdn.net/ajax/libs/elliptic/6.5.6/elliptic.js）
const EC = elliptic.ec;
const ec = new EC('p256'); // P-256曲线
// 生成密钥对
const keyPair = ec.genKeyPair();
const publicKey = keyPair.getPublic().getX().toString('hex') + "|" + keyPair.getPublic().getY().toString('hex');
共享密钥计算
后端
public static String caculateShareKey(String serverPrivateKey,String receivePublicKey){
String shareKey = "";
try{
// 1. 后端私钥 Base64 字符串
// 2. 从 Base64 恢复后端私钥
ECPrivateKey privKey = loadPrivateKeyFromBase64(serverPrivateKey);
// 3. 前端传递的公钥坐标 (x 和 y 坐标，假设为十六进制字符串)
// 假设这是从前端接收到的公钥的 x 和 y 坐标
String xHex = receivePublicKey.split("\\|")[0]; // 用前端传递的 x 坐标替换
String yHex = receivePublicKey.split("\\|")[1]; // 用前端传递的 y 坐标替换
// 4. 将 x 和 y 转换为 BigInteger
BigInteger x = new BigInteger(xHex, 16);
BigInteger y = new BigInteger(yHex, 16);
// 5. 创建 ECPoint 对象 (公钥坐标)
ECPoint ecPoint = new ECPoint(x, y);
// 6. 获取 EC 参数（例如 secp256r1）
ECParameterSpec ecSpec = getECParameterSpec();
// 7. 恢复公钥
ECPublicKey pubKey = recoverPublicKey(ecPoint, ecSpec);
// 8. 使用 ECDH 计算共享密钥
byte[] sharedSecret = calculateSharedSecret(privKey, pubKey);
// 9. 打印共享密钥
shareKey = bytesToHex(sharedSecret);
}catch (Exception e){
e.printStackTrace();
}
return shareKey;
}
// 从 Base64 加载 ECPrivateKey
private static ECPrivateKey loadPrivateKeyFromBase64(String privateKeyBase64) throws Exception {
byte[] decodedKey = Base64.getDecoder().decode(privateKeyBase64);
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(decodedKey);
KeyFactory keyFactory = KeyFactory.getInstance("EC");
return (ECPrivateKey) keyFactory.generatePrivate(keySpec);
}
// 获取 EC 参数（例如 secp256r1）
private static ECParameterSpec getECParameterSpec() throws Exception {
// 手动指定 EC 曲线（例如 secp256r1）
AlgorithmParameters params = AlgorithmParameters.getInstance("EC");
params.init(new ECGenParameterSpec("secp256r1")); // 使用标准的 P-256 曲线
return params.getParameterSpec(ECParameterSpec.class);
}
// 恢复公钥
private static ECPublicKey recoverPublicKey(ECPoint ecPoint, ECParameterSpec ecSpec) throws Exception {
ECPublicKeySpec pubKeySpec = new ECPublicKeySpec(ecPoint, ecSpec);
KeyFactory keyFactory = KeyFactory.getInstance("EC");
return (ECPublicKey) keyFactory.generatePublic(pubKeySpec);
}
// 使用 ECDH 计算共享密钥
private static byte[] calculateSharedSecret(ECPrivateKey privKey, ECPublicKey pubKey) throws Exception {
KeyAgreement keyAgreement = KeyAgreement.getInstance("ECDH");
keyAgreement.init(privKey);
keyAgreement.doPhase(pubKey, true);
return keyAgreement.generateSecret();
}
// 将字节数组转换为十六进制字符串
private static String bytesToHex(byte[] bytes) {
StringBuilder hexString = new StringBuilder();
for (byte b : bytes) {
hexString.append(String.format("%02x", b));
}
return hexString.toString();
}
前端
var keyArray = serverPublicPointKey.split("|")
const otherKey = ec.keyFromPublic({ x: keyArray[0], y: keyArray[1] }, 'hex');
const sharedSecret = keyPair.derive(otherKey.getPublic());
AES加密
后端
public static String encryptData(String data,String shareKey){
String result = "";
try{
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] aesKey = digest.digest(shareKey.getBytes()); // 获取 256 位密钥
SecretKey key = new SecretKeySpec(aesKey, "AES");
byte[] resultData = encrypt(data,key);
result = Base64.getEncoder().encodeToString(resultData);
}catch (Exception e){
e.printStackTrace();
}
return result;
}
public static String decryptData(String data,String shareKey){
String result = "";
try{
MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] aesKey = digest.digest(shareKey.getBytes()); // 获取 256 位密钥
SecretKey key = new SecretKeySpec(aesKey, "AES");
byte[] resultData = decrypt(Base64.getDecoder().decode(data),key);
result = new String(resultData);
}catch (Exception e){
e.printStackTrace();
}
return result;
}
private static final String KEY_ALGORITHM = "AES";
private static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
private static final String IV = "0102030405060708"; // 16 bytes key
// 使用AES密钥加密数据
private static byte[] encrypt(String plaintext, SecretKey aesKey) throws Exception {
SecretKeySpec keySpec = new SecretKeySpec(aesKey.getEncoded(), KEY_ALGORITHM);
IvParameterSpec iv = new IvParameterSpec(IV.getBytes());
Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv);
byte[] encrypted = cipher.doFinal(plaintext.getBytes());
return encrypted;
}
// 使用AES密钥解密数据
private static byte[] decrypt(byte[] encryptedData, SecretKey aesKey) throws Exception {
SecretKeySpec keySpec = new SecretKeySpec(aesKey.getEncoded(), KEY_ALGORITHM);
IvParameterSpec iv = new IvParameterSpec(IV.getBytes());
Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, keySpec, iv);
byte[] original = cipher.doFinal(encryptedData);
return original;
}
前端
引入crypto-js.min.js（https://cdnjs.cloudflare.com/ajax/libs/crypto-js/4.1.1/crypto-js.min.js）
function encryptByECDH(message, shareKey) {
const aesKey = CryptoJS.SHA256(shareKey);
const key = CryptoJS.enc.Base64.parse(aesKey.toString(CryptoJS.enc.Base64));
return encryptByAES(message,key)
}
function decryptByECDH(message, shareKey) {
const aesKey = CryptoJS.SHA256(shareKey);
const key = CryptoJS.enc.Base64.parse(aesKey.toString(CryptoJS.enc.Base64));
return decryptByAES(message,key)
}
function encryptByAES(message, key) {
const iv = CryptoJS.enc.Utf8.parse("0102030405060708");
const encrypted = CryptoJS.AES.encrypt(message, key, { iv: iv , mode: CryptoJS.mode.CBC, padding: CryptoJS.pad.Pkcs7 });
return encrypted.toString();
}
function decryptByAES(message, key) {
const iv = CryptoJS.enc.Utf8.parse("0102030405060708");
const bytes = CryptoJS.AES.decrypt(message, key, { iv: iv, mode: CryptoJS.mode.CBC, padding: CryptoJS.pad.Pkcs7 });
const originalText = bytes.toString(CryptoJS.enc.Utf8);
return originalText;
}
注意
- 前端生成的密钥对和后端生成的密钥对形式不一致，需要将前端的公钥拆解成坐标点到后端进行公钥还原
- 同理后端的公钥也要拆分成坐标点传输到前端进行计算
- 生成的ShareKey共享密钥为了满足AES的密钥长度要求需要进行Share256计算
- 前后端AES互通需要保证IV向量为同一值
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