RSA加密长度限制问题
RSA加解密中必须考虑到的密钥长度、明文长度和密文长度问题。明文长度需要小于密钥长度,而密文长度则等于密钥长度。因此当加密内容长度大于密钥长度时,有效的RSA加解密就需要对内容进行分段。
这是因为,RSA算法本身要求加密内容也就是明文长度m必须0
这样,对于1024长度的密钥。128字节(1024bits)-减去11字节正好是117字节,但对于RSA加密来讲,padding也是参与加密的,所以,依然按照1024bits去理解,但实际的明文只有117字节了。
所以如果要对任意长度的数据进行加密,就需要将数据分段后进行逐一加密,并将结果进行拼接。同样,解码也需要分段解码,并将结果进行拼接。
/***
* @Descriptions rsa 加解密类
* @Create 阿汤哥
* @Date: 2020/6/10 14:03
* @Company
* @version V1.0.0
**/
public class RSAEncrypt {
public static final String CHARSET = "UTF-8";
public static final String RSA_ALGORITHM = "RSA"; //
public static Map createKeys(int keySize) {
// 为RSA算法创建一个KeyPairGenerator对象
KeyPairGenerator kpg;
try {
kpg = KeyPairGenerator.getInstance(RSA_ALGORITHM);
} catch (NoSuchAlgorithmException e) {
throw new IllegalArgumentException("No such algorithm-->[" + RSA_ALGORITHM + "]");
}
// 初始化KeyPairGenerator对象,密钥长度
kpg.initialize(keySize);
// 生成密匙对
KeyPair keyPair = kpg.generateKeyPair();
// 得到公钥
Key publicKey = keyPair.getPublic();
String publicKeyStr = Base64.encodeBase64URLSafeString(publicKey.getEncoded());
// 得到私钥
Key privateKey = keyPair.getPrivate();
String privateKeyStr = Base64.encodeBase64URLSafeString(privateKey.getEncoded());
// map装载公钥和私钥
Map keyPairMap = new HashMap();
keyPairMap.put("publicKey", publicKeyStr);
keyPairMap.put("privateKey", privateKeyStr);
// 返回map
return keyPairMap;
}
/**
* 得到公钥
* @param publicKey 密钥字符串(经过base64编码)
* @throws Exception
*/
public static RSAPublicKey getPublicKey(String publicKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
// 通过X509编码的Key指令获得公钥对象
KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(Base64.decodeBase64(publicKey));
RSAPublicKey key = (RSAPublicKey) keyFactory.generatePublic(x509KeySpec);
return key;
}
/**
* 得到私钥
* @param privateKey 密钥字符串(经过base64编码)
* @throws Exception
*/
public static RSAPrivateKey getPrivateKey(String privateKey) throws NoSuchAlgorithmException, InvalidKeySpecException {
// 通过PKCS#8编码的Key指令获得私钥对象
KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(Base64.decodeBase64(privateKey));
RSAPrivateKey key = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8KeySpec);
return key;
}
/**
* 公钥加密
* @param data
* @param publicKey
* @return
*/
public static String publicEncrypt(String data, RSAPublicKey publicKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), publicKey.getModulus().bitLength()));
} catch (Exception e) {
throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 私钥解密
* @param data
* @param privateKey
* @return
*/
public static String privateDecrypt(String data, RSAPrivateKey privateKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), privateKey.getModulus().bitLength()), CHARSET);
} catch (Exception e) {
throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 私钥加密
* @param data
* @param privateKey
* @return
*/
public static String privateEncrypt(String data, RSAPrivateKey privateKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
//每个Cipher初始化方法使用一个模式参数opmod,并用此模式初始化Cipher对象。此外还有其他参数,包括密钥key、包含密钥的证书certificate、算法参数params和随机源random。
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
return Base64.encodeBase64URLSafeString(rsaSplitCodec(cipher, Cipher.ENCRYPT_MODE, data.getBytes(CHARSET), privateKey.getModulus().bitLength()));
} catch (Exception e) {
throw new RuntimeException("加密字符串[" + data + "]时遇到异常", e);
}
}
/**
* 公钥解密
* @param data
* @param publicKey
* @return
*/
public static String publicDecrypt(String data, RSAPublicKey publicKey) {
try {
Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, publicKey);
return new String(rsaSplitCodec(cipher, Cipher.DECRYPT_MODE, Base64.decodeBase64(data), publicKey.getModulus().bitLength()), CHARSET);
} catch (Exception e) {
throw new RuntimeException("解密字符串[" + data + "]时遇到异常", e);
}
}
//rsa切割解码 , ENCRYPT_MODE,加密数据 ,DECRYPT_MODE,解密数据
private static byte[] rsaSplitCodec(Cipher cipher, int opmode, byte[] datas, int keySize) {
int maxBlock = 0; //最大块
if (opmode == Cipher.DECRYPT_MODE) {
maxBlock = keySize / 8;
} else {
maxBlock = keySize / 8 - 11;
}
ByteArrayOutputStream out = new ByteArrayOutputStream();
int offSet = 0;
byte[] buff;
int i = 0;
try {
while (datas.length > offSet) {
if (datas.length - offSet > maxBlock) {
//可以调用以下的doFinal()方法完成加密或解密数据:
buff = cipher.doFinal(datas, offSet, maxBlock);
} else {
buff = cipher.doFinal(datas, offSet, datas.length - offSet);
}
out.write(buff, 0, buff.length);
i++;
offSet = i * maxBlock;
}
} catch (Exception e) {
throw new RuntimeException("加解密阀值为[" + maxBlock + "]的数据时发生异常", e);
}
byte[] resultDatas = out.toByteArray();
IOUtils.closeQuietly(out);
return resultDatas;
}
// 简单测试____________
public static void main(String[] args) throws Exception {
Map keyMap = createKeys(1024);
String publicKey = keyMap.get("publicKey");
String privateKey = keyMap.get("privateKey");
System.out.println("公钥: \n\r" + publicKey);
System.out.println("私钥: \n\r" + privateKey);
System.out.println("公钥加密——私钥解密");
String str = "这是一个明文测试字符串,如果明文太长才回分段加密";
System.out.println("\r明文:\r\n" + str);
System.out.println("\r明文大小:\r\n" + str.getBytes().length);
String encodedData = publicEncrypt(str, getPublicKey(publicKey)); //传入明文和公钥加密,得到密文
System.out.println("密文:\r\n" + encodedData);
String decodedData = privateDecrypt(encodedData, getPrivateKey(privateKey)); //传入密文和私钥,得到明文
System.out.println("解密后文字: \r\n" + decodedData);
System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>");
}
}