README

When messages are passed between two systems over a public network, encryption tools are needed to protect the content in transit. Encrypting and decrypting messages correctly can be fiddly and error-prone, so this library keeps the process small and explicit through the PlainTextMessage, EncryptedMessage, CipherText, Key, and InitVector abstractions.

Pass your secret message to the PlainTextMessage constructor, then call encrypt() with a shared Key to produce a CipherText. The encrypted payload is represented by the cipher text itself plus the IV returned by getIv(). Those values can then be passed to the receiver by any communication mechanism, with only the holder of the same shared key able to decrypt the original message.

On the receiving side, construct an EncryptedMessage with the incoming cipher text and IV, then call decrypt() with the same Key to recover the original plain text.

The CipherText class also provides a getUri() method for creating a pre-encoded URI. A URI containing cipher and iv query string parameters can then be passed to EncryptedUri and decrypted back into a PlainTextMessage.

Example usage: transmit an encrypted message over a query string

sender.php:

use \GT\Cipher\Message\PlainTextMessage;
use \GT\Cipher\Message\EncryptedMessage;

$privateKey = "This can be any string, but a long random string is best.";

$message = new PlainTextMessage("Hello, PHP.Gt!");
$cipherText = $message->encrypt($privateKey);
header("Location: " . $cipherText->getUri("/receiver.php"));

receiver.php:

// This key must be the same on the sender and receiver!
use GT\Cipher\EncryptedUri;

$privateKey = "This can be any string, but a long random string is best.";

$uri = new EncryptedUri($_SERVER["REQUEST_URI"]);
$plainText = $uri->decryptMessage($privateKey);
echo $plainText;
// Output: Hello, PHP.Gt!

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