function encrypt($originalData){
    $publicKeyFilePath = '/www/ceshi/rsa_public_key.pem';
    extension_loaded('openssl') or die('php需要openssl扩展支持');
    file_exists($publicKeyFilePath) or die('公钥的文件路径不正确');
    $publicKey = openssl_pkey_get_public(file_get_contents($publicKeyFilePath));
    $publicKey or die('公钥不可用');
    $crypto = '';
    foreach (str_split($originalData, 117) as $chunk) {
        $encryptData = '';
        if(openssl_public_encrypt($chunk, $encryptData, $publicKey)){
            $crypto .= $encryptData;
        }else{
            die('加密失败');
        }
    }
    return base64_encode($crypto);
}

function decrypt($encryptData){
    $privateKeyFilePath = '/www/ceshi/rsa_private_key.pem';
    extension_loaded('openssl') or die('php需要openssl扩展支持');
    file_exists($privateKeyFilePath) or die('密钥的文件路径不正确');
    $privateKey = openssl_pkey_get_private(file_get_contents($privateKeyFilePath));
    $privateKey or die('密钥不可用');
    $decryptData = '';
    $crypto = '';
    foreach (str_split(base64_decode($encryptData), 128) as $chunk) {
        if(openssl_private_decrypt($chunk, $decryptData, $privateKey)){
            $crypto .= $decryptData;
        }else{
            die('解密失败');
        }

    }
    return $crypto;
}

$aa = encrypt('aa');
$bb = decrypt($aa);
var_dump($bb);
输出的结果为：aa