PHP：ASCII和UTF-8字符串比较

Question

I have following test.php script:

$AES_IV = "4epZqMl8BQukhip6WQjQHg==";
$AES_KEY = "zvKmer0cPiJdQQ1RPjQOCF/wURt+31UdingRoPj4+Yc=";

$guid = $_GET["guid"];
$encryptedGuid = urldecode($_GET["encryptedGuid"]);

$decryptedGuid = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, base64_decode($AES_KEY), base64_decode($encryptedGuid), MCRYPT_MODE_CBC, base64_decode($AES_IV));

echo "Guid is: ".$guid."</br>";
echo "Decrypted GUID is: ".$decryptedGuid."</br>";

if ($decryptedGuid === $guid)
{
    echo "Guid and decrypted Guid are equals.";
}
else 
{
    echo "Guid and decrypted Guid are not equals.";
}

I call this script as follows:

http://localhost:8087/test/test.php?guid=08201E62-DFA5-8A50-ACFC-A811871804CD&encryptedGuid=ED40y72BJvzXmN0Aj9eb85VdIJKu6LUYQuYSWMPOhIQcm5SIquZAhRMmhsC7ax2e

Test.php script should display "Guid and decrypted Guid are equals." but it never occurs. I tried to check encoding of strings and $guid is ASCII and $encryptedGuid is UTF-8. Can you please help me how to solve this problem? I tried to convert ASCII to UTF-8 but I wasn't successful because result of e.g. iconv function was again ASCII. I think convert ASCII to UTF-8 can be solution but I am not sure if it is always true that $_GET returns ASCII.

Thank you very much for your help.

Answer 1

I had a similar issue and I was able to work it out thanks to Dennis' comment about padding.

After I decrypted my AES string and I noticed that one particular param in the URL wasn't quite right...

E.g. test=1&foo=bar

It looked fine. However, when I was trying to do a string comparison with the final value in the URL (bar) it would never be true.

if ($foo == 'bar')

So, I compared the strings using bin2hex there was some sort of repeated string added to the end of the param value (0505050505). What I didn't realise was that this was padding added to the string by the encryption.

For some reason rtrim didn't help me so what I did was added a useless param to the end of my URL before encryption (e.g. padding=1). This made sure that the last of my "important" params didn't have the padding added to the string.