RSA 签名

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public class RSA{

/**
* RSA签名
* @param content 待签名数据
* @param privateKey 商户私钥
* @param input_charset 编码格式
* @return 签名值
*/
public static String sign(String content, String privateKey, String input_charset)
{
try
{
  PKCS8EncodedKeySpec priPKCS8 = new PKCS8EncodedKeySpec( Base64.decode(privateKey) );
  KeyFactory keyf = KeyFactory.getInstance("RSA");
  PrivateKey priKey = keyf.generatePrivate(priPKCS8);

java.security.Signature signature = java.security.Signature.getInstance(SIGN_ALGORITHMS);

signature.initSign(priKey);
signature.update( content.getBytes(input_charset) );

byte[] signed = signature.sign();

return Base64.encode(signed);
}
catch (Exception e)
{
  e.printStackTrace();
}

return null;
}

/**
* RSA验签名检查
* @param content 待签名数据
* @param sign 签名值
* @param ali_public_key 商户公钥
* @param input_charset 编码格式
* @return 布尔值
*/
public static boolean verify(String content, String sign, String ali_public_key, String input_charset)
{
try
{
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
byte[] encodedKey = Base64.decode(ali_public_key);
PublicKey pubKey = keyFactory.generatePublic(new X509EncodedKeySpec(encodedKey));

java.security.Signature signature = java.security.Signature
.getInstance(SIGN_ALGORITHMS);

signature.initVerify(pubKey);
signature.update( content.getBytes(input_charset) );

boolean bverify = signature.verify( Base64.decode(sign) );
return bverify;

}
catch (Exception e)
{
e.printStackTrace();
}

return false;
}

/**
* 解密
* @param content 密文
* @param private_key 商户私钥
* @param input_charset 编码格式
* @return 解密后的字符串
*/
public static String decrypt(String content, String private_key, String input_charset) throws Exception {
PrivateKey prikey = getPrivateKey(private_key);

Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, prikey);

InputStream ins = new ByteArrayInputStream(Base64.decode(content));
ByteArrayOutputStream writer = new ByteArrayOutputStream();
//rsa解密的字节大小最多是128，将需要解密的内容，按128位拆开解密
byte[] buf = new byte[128];
int bufl;

while ((bufl = ins.read(buf)) != -1) {
byte[] block = null;

if (buf.length == bufl) {
block = buf;
} else {
block = new byte[bufl];
for (int i = 0; i < bufl; i++) {
block[i] = buf[i];
}
}

writer.write(cipher.doFinal(block));
}

return new String(writer.toByteArray(), input_charset);
}

/**
* 得到私钥
* @param key 密钥字符串（经过base64编码）
* @throws Exception
*/
public static PrivateKey getPrivateKey(String key) throws Exception {

byte[] keyBytes;
keyBytes = Base64.decode(key);

PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");

PrivateKey privateKey = keyFactory.generatePrivate(keySpec);

return privateKey;
}
}

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