RSA符号函数问题

我正在开发一个RSA sign（）函数，用于为私有流生成签名的URL。我在测试PHP代码，但我想在Flex中重新编写代码。以下是PHP代码的一部分：

function getCannedPolicy($resource, $expires, $key, $privatekeyfile){
         $priv_key = file_get_contents($privatekeyfile);
         $pkeyid = openssl_get_privatekey($priv_key);
         $policy_str = '{"Statement":[{"Resource":"'.$resource.'","Condition":{"DateLessThan":{"AWS:EpochTime":'.$expires.'}}}]}';
         $policy_str = trim( preg_replace( '/'s+/', '', $policy_str ) );
         $res = openssl_sign($policy_str, $signature, $pkeyid, OPENSSL_ALGO_SHA1);
         $signature_base64 = (base64_encode($signature));
         $repl = array('+' => '-','=' => '_','/' => '~');
         $signature_base64 = strtr($signature_base64,$repl);
         $url = $resource . '?Expires='.$expires. '&Signature=' . $signature_base64 . '&Key-Pair-Id='. $key;
         return $url;
}

我在Flex中编写了相同的函数。这是代码：

private function getCannedPolicy(resource:String, expires:uint, key:String, privatekey:String):String{          
    var unsigned:String = '{"Statement":[{"Resource":"' +resource+ '","Condition":{"DateLessThan":{"AWS:EpochTime":' +expires+ '}}}]}';
    var signed:String = '';
    var signature:String = '';
    var regex:RegExp = /'s+/g;          
    unsigned = unsigned.replace(regex,'');
    var src:ByteArray = new ByteArray();            
    src.writeUTFBytes(unsigned);            
    var dst:ByteArray = new ByteArray();            
    var hash:SHA1 = new SHA1();
    src = hash.hash(src);                       
    var rsa:RSAKey = PEM.readRSAPrivateKey(privatekey);
    trace(rsa.dump());
    rsa.sign(src, dst, src.length);
    dst.position = 0;           
    signature = Base64.encodeByteArray(dst);                            
    signature = signature.split("+").join("-");
    signature = signature.split("=").join("_");
    signature = signature.split("'/").join("~");
    signed = resource+'?Expires=' +expires+ '&Signature=' +signature+ '&Key-Pair-Id=' +key; 
    return signed;
}

两个函数（PHP和Flex）的输出格式相同。但是，当我使用Flex函数中的签名URL时，流不起作用。

我对openssl_sign（）php函数使用的替代方法是as3crypto库中的sign（）函数。也许问题出在这里？也许加密不同。