一、已有公钥私钥
1、私钥解密

$privKey = '
-----BEGIN RSA PRIVATE KEY-----
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
-----END RSA PRIVATE KEY-----';

$public_key = '-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCyp9MOfDyk0LJiW2337oXmcDztbsiOmSnhR+Rsb/ioTQ2tdI0WSPhkBOB4FjPrSkHrDcU/wwmw40e/Y4ecMiYKqFEgGMAIs2P06niCH7N9QLM3mzMBSxnNq++fLbC46KVjvw2lKunpo3YHJQAay7MbyyChqH+xl1xYZs3NKyHNowIDAQAB
-----END PUBLIC KEY-----';

$data = "已被加密的数据";

/**
 * RSA私钥加密
 * @param string $private_key 私钥
 * @param string $data 要加密的字符串
 * @return string $encrypted 返回加密后的字符串
 * @author mosishu
 */
function privateEncrypt($private_key,$data){
    $encrypted = '';
    $pi_key = openssl_pkey_get_private($private_key);//这个函数可用来判断私钥是否是可用的，可用返回资源id Resource id
 //最大允许加密长度为117，得分段加密
    $plainData = str_split($data, 100);//生成密钥位数 1024 bit key
    foreach($plainData as $chunk){
        $partialEncrypted = '';
        $encryptionOk = openssl_private_encrypt($chunk,$partialEncrypted,$pi_key);//私钥加密
        if($encryptionOk === false){
           return false;
        }
        $encrypted .= $partialEncrypted;
   }
    $encrypted = base64_encode($encrypted);//加密后的内容通常含有特殊字符，需要编码转换下，在网络间通过url传输时要注意base64编码是否是url安全的
    return $encrypted;
}

/**
 * RSA公钥解密(私钥加密的内容通过公钥可以解密出来)
 * @param string $public_key 公钥
 * @param string $data 私钥加密后的字符串
 * @return string $decrypted 返回解密后的字符串
 * @author mosishu
 */
function publicDecrypt($public_key,$data){
    $decrypted = '';
    $pu_key = openssl_pkey_get_public($public_key);//这个函数可用来判断公钥是否是可用的
    $plainData = str_split(base64_decode($data), 128);//生成密钥位数 1024 bit key
    foreach($plainData as $chunk){
    $str = '';
    $decryptionOk = openssl_public_decrypt($chunk,$str,$pu_key);//公钥解密
    if($decryptionOk === false){
        return false;
    }
    $decrypted .= $str;
  }
  return $decrypted;
}

//RSA公钥加密
function publicEncrypt($public_key,$data){
    $encrypted = '';
    $pu_key = openssl_pkey_get_public($public_key);
    $plainData = str_split($data, 100);
    foreach($plainData as $chunk){
         $partialEncrypted = '';
         $encryptionOk = openssl_public_encrypt($chunk,$partialEncrypted,$pu_key);//公钥加密
         if($encryptionOk === false){
             return false;
         }
         $encrypted .= $partialEncrypted;
    }
    $encrypted = base64_encode($encrypted);
    return $encrypted;
}

// RSA私钥解密
function privateDecrypt($private_key,$data){
    $decrypted = '';
    $pi_key = openssl_pkey_get_private($private_key);
    $plainData = str_split(base64_decode($data), 128);
    foreach($plainData as $chunk){
        $str = '';
        $decryptionOk = openssl_private_decrypt($chunk,$str,$pi_key);//私钥解密
        if($decryptionOk === false){
            return false;
        }
        $decrypted .= $str;
    }
    return $decrypted;
}

二、已有公钥私钥文件