Eu tenho tentado implementar a técnica de criptografia / descriptografia mcrypt no servidor, PHP e no cliente. Estou tentando usarmcrypt.js biblioteca no momento como:

<?php 
$key = 'testtesttesttesttesttesttesttest';

function string_encrypt($string, $key) {
    $crypted_text = mcrypt_encrypt(
                        MCRYPT_RIJNDAEL_128, 
                        $key, 
                        $string, 
                        MCRYPT_MODE_ECB
                    );
    return base64_encode($crypted_text);
}

function string_decrypt($encrypted_string, $key) {
    $decrypted_text = mcrypt_decrypt(
                        MCRYPT_RIJNDAEL_128, 
                        $key, 
                        base64_decode($encrypted_string), 
                        MCRYPT_MODE_ECB
                    );
    return trim($decrypted_text);
}

echo 'Provided Text:    '.$test_str = 'This is test message.';
echo '<br />';
echo 'Encyrpted Value:  '.$enc_str = string_encrypt($test_str, $key);   
echo '<br />';
echo 'Decrypted Value:  '.string_decrypt($enc_str, $key);                               
echo '<br />';
?>

<script src='rijndael.js'></script>
<script src='mcrypt.js'></script>
<script src='base64v1_0.js'></script>

<script lang='javascript'>
    var enc_str = mcrypt.Encrypt('<?php echo $test_str ?>','');
    enc_str = B64.encode(enc_str);
    alert(enc_str); 
    // I don't get this same as encypted PHP text. i.e. $enc_str
    var dec_str = B64.decode('<?php echo $enc_str ?>');
    alert(mcrypt.Decrypt(dec_str,'')); 
    // I don't get this same as decypted PHP text. 
    // i.e. string_decrypt($enc_str)
</script>

Eu usei esses vars particulares a seguir na biblioteca mcrypt.js.

 var cMode='ecb';
 var cCipher='rijndael-256';
 var cKey='testtesttesttesttesttesttesttest'; 
 //I am providing the same key

Como comentei acima, por que éenc_str não é igual a$enc_str e porque émcrypt.Decrypt('<?php echo $enc_str ?>', '') não é igual astring_decrypt($enc_str, $key) ?

Pergunta atualizada:

Tentei codificar / decodificar base64 e até hex2bin / bin2hex para analisar essas cadeias, mas essas duas produziram os seguintes resultados:

Usando Hex2bin / Bin2hex

Resultado PHP:

Provided Text: This is test message.
Encyrpted Value: a51e970427ec8f666a5684cc1712ad03b29889cc10f4ccbf55733564d11c0386
Decrypted Value: This is test message.

Resultado JS:

Provided Text:This is test message.
Mcrypted value:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Encyrpted Value:a51e970427ec8f666a5684cc1712ad03b29889cc10f4ccbf55733564d11c0386
After Hex to Bin Text:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Decrypted Value:This is test message.�����������
/*These diamond with question mark is produced while decypting the value.*/

Usando codificação / decodificação Base64:

Resultado PHP:

Provided Text: This is test message.
Mcrypt encrypted value : ¥—'ìfjV„Ì­²˜‰ÌôÌ¿Us5dц
/*
 Here mcrypted value provided by JS and PHP is different
 That is causing to produce different value at two ends
*/
Encyrpted Value: pR6XBCfsj2ZqVoTMFxKtA7KYicwQ9My/VXM1ZNEcA4Y=
Decrypted Value: This is test message.

Resultado JS:

Provided Text:This is test message.
Mcrypted value:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ
Encyrpted Value:wqUewpcEJ8Oswo9malbChMOMFxLCrQPCssKYwonDjBDDtMOMwr9VczVkw5EcA8KG
After Base64 Decode:¥'ìfjVÌ­²ÌôÌ¿Us5dÑ���
Decrypted Value:This is test message.�����������bFaêF«+JéÓ!ÆÖ

E nos dois casos, o conteúdo UTf-8 não pode ser descriptografado no final do JS.

* Links: *

Biblioteca JS Mcrypt

Biblioteca JS Base64