java 使用pem密钥进行RSA加解密

1.使用openssl生成私钥和公钥

openssl下载地址：http://www.openssl.org/source

openssl生成私钥命令： genrsa -out rsa_private_key.pem 1024

openssl生成公钥命令： rsa -in rsa_private_key.pem -pubout -out rsa_public_key.pem

2.此时在openssl安装目录下的bin文件夹可以看到 rsa_private_key.pem 和 rsa_public_key.pem 两个文件。这时候的私钥是不能直接使用的，需要进行 pkcs8 编码

openssl的pkcs8编码命令：pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt

那么在bin文件夹可以看到 pkcs8_rsa_private_key.pem 文件。至此，可用的密钥对已经生成好了，私钥使用pkcs8_rsa_private_key.pem，公钥采用rsa_public_key.pem。

3.使用密钥对进行签名、加解密

public class RSAPemCoder {
public static final String KEY_SHA = "SHA";
public static final String KEY_MD5 = "MD5";
public static final String KEY_ALGORITHM = "RSA";
public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

/**
* 用私钥对信息生成数字签名
*
* @param data 加密数据
* @param privateKey 私钥
* @return
* @throws Exception
*/
public static String sign(byte[] data, PrivateKey privateKey) throws Exception {
Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
signature.initSign(privateKey);
signature.update(data);
return encryptBASE64(signature.sign());
}

/**
* 校验数字签名
*
* @param data 加密数据
* @param publicKey 公钥
* @param sign 数字签名
* @return 校验成功返回true 失败返回false
* @throws Exception
*/
public static boolean verify(byte[] data, PublicKey publicKey, String sign) throws Exception {
Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
signature.initVerify(publicKey);
signature.update(data);
return signature.verify(decryptBASE64(sign));
}

/**
* 私钥解密
*
* @param data 密文
* @param PrivateKey 私钥
* @return
* @throws Exception
*/
public static byte[] decryptByPrivateKey(byte[] data, PrivateKey privateKey) throws Exception {
KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return cipher.doFinal(data);
}

/**
* 用公钥解密
*
* @param data 密文
* @param publicKey 公钥
* @return
* @throws Exception
*/
public static byte[] decryptByPublicKey(byte[] data, PublicKey publicKey) throws Exception {
KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
cipher.init(Cipher.DECRYPT_MODE, publicKey);
return cipher.doFinal(data);
}

/**
* 用公钥加密
*
* @param data 明文
* @param PublicKey 公钥
* @return
* @throws Exception
*/
public static byte[] encryptByPublicKey(byte[] data, PublicKey publicKey) throws Exception {
KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return cipher.doFinal(data);
}

/**
* 用私钥加密
*
* @param data 明文
* @param privateKey 私钥
* @return
* @throws Exception
*/
public static byte[] encryptByPrivateKey(byte[] data, PrivateKey privateKey) throws Exception {
KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
cipher.init(Cipher.ENCRYPT_MODE, privateKey);
return cipher.doFinal(data);
}

public static PrivateKey getPrivateKeyFromPem() throws Exception {
BufferedReader br = new BufferedReader(new FileReader("e:/pkcs8_privatekey.pem"));
String s = br.readLine();
String str = "";
s = br.readLine();
while (s.charAt(0) != '-') {
str += s + "\r";
s = br.readLine();
}
BASE64Decoder base64decoder = new BASE64Decoder();
byte[] b = base64decoder.decodeBuffer(str);

// 生成私匙
KeyFactory kf = KeyFactory.getInstance("RSA");
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(b);
PrivateKey privateKey = kf.generatePrivate(keySpec);
return privateKey;
}

public static PublicKey getPublicKeyFromPem() throws Exception {
BufferedReader br = new BufferedReader(new FileReader("e:/publickey.pem"));
String s = br.readLine();
String str = "";
s = br.readLine();
while (s.charAt(0) != '-') {
str += s + "\r";
s = br.readLine();
}
BASE64Decoder base64decoder = new BASE64Decoder();
byte[] b = base64decoder.decodeBuffer(str);
KeyFactory kf = KeyFactory.getInstance("RSA");
X509EncodedKeySpec keySpec = new X509EncodedKeySpec(b);
PublicKey pubKey = kf.generatePublic(keySpec);
return pubKey;
}

public static byte[] decryptBASE64(String key) throws Exception {
return (new BASE64Decoder()).decodeBuffer(key);
}

public static String encryptBASE64(byte[] key) throws Exception {
return (new BASE64Encoder()).encodeBuffer(key);
}

public static byte[] encryptMD5(byte[] data) throws Exception {

MessageDigest md5 = MessageDigest.getInstance(KEY_MD5);
md5.update(data);

return md5.digest();

}

public static byte[] encryptSHA(byte[] data) throws Exception {

MessageDigest sha = MessageDigest.getInstance(KEY_SHA);
sha.update(data);

return sha.digest();

}
}