PHP

Example: Crypt2.RandomizeIV method

Demonstrates using a random initialization vector for AES GCM encryption. Chilkat2 PHP

<?php

use Chilkat2\BinData;
use Chilkat2\Crypt2;

// This example assumes the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

$crypt = new Crypt2();

$crypt->CryptAlgorithm = 'aes';
$crypt->CipherMode = 'gcm';
$crypt->KeyLength = 256;

$K = '000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F';
$AAD = 'feedfacedeadbeeffeedfacedeadbeefabaddad2';
$PT = 'This is the text to be AES-GCM encrypted.';

// Generate a random IV.
$crypt->RandomizeIV();
$IV = $crypt->GetEncodedIV('hex');

$crypt->SetEncodedKey($K, 'hex');

$crypt->SetEncodedAad($AAD, 'hex');

// Return the encrypted bytes as base64
$crypt->EncodingMode = 'base64';
$crypt->Charset = 'utf-8';
try {
    $cipherText = $crypt->EncryptStringENC($PT);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

// Get the GCM authenticated tag computed when encrypting.
$authTag = $crypt->GetEncodedAuthTag('base64');

echo 'Cipher Text: ', $cipherText, "\n";
echo 'Auth Tag: ', $authTag, "\n";

// Let's send the IV, CipherText, and AuthTag to the decrypting party.
// We'll send them concatenated like this: [IV || Ciphertext || AuthTag]
// In base64 format.
$bdEncrypted = new BinData();
$bdEncrypted->AppendEncoded($IV, 'hex');
$bdEncrypted->AppendEncoded($cipherText, 'base64');
$bdEncrypted->AppendEncoded($authTag, 'base64');

$concatenatedGcmOutput = $bdEncrypted->GetEncoded('base64');
echo 'Concatenated GCM Output: ', $concatenatedGcmOutput, "\n";

// Sample output so far:

// -------------------------------------------------------------------------------------
// Now let's GCM decrypt...
// -------------------------------------------------------------------------------------

$decrypt = new Crypt2();

// The values shared and agreed upon by both sides beforehand are: algorithm, cipher mode, secret key, and AAD.
// Sometimes the IV can be a value already known and agreed upon, but in this case the encryptor sends the IV to the decryptor.
$decrypt->CryptAlgorithm = 'aes';
$decrypt->CipherMode = 'gcm';
$decrypt->KeyLength = 256;
$decrypt->SetEncodedKey($K, 'hex');
$decrypt->SetEncodedAad($AAD, 'hex');

$bdFromEncryptor = new BinData();
$bdFromEncryptor->AppendEncoded($concatenatedGcmOutput, 'base64');

$sz = $bdFromEncryptor->NumBytes;

// Extract the parts.
$extractedIV = $bdFromEncryptor->GetEncodedChunk(0, 16, 'hex');
$extractedCipherText = $bdFromEncryptor->GetEncodedChunk(16, $sz - 32, 'base64');
$expectedAuthTag = $bdFromEncryptor->GetEncodedChunk($sz - 16, 16, 'base64');

// Before GCM decrypting, we must set the authenticated tag to the value that is expected.
// The decryption will fail if the resulting authenticated tag is not equal to the expected result.
$decrypt->SetEncodedAuthTag($expectedAuthTag, 'base64');

// Also set the IV.
$decrypt->SetEncodedIV($extractedIV, 'hex');

// Decrypt..
$decrypt->EncodingMode = 'base64';
$decrypt->Charset = 'utf-8';
try {
    $decryptedText = $decrypt->DecryptStringENC($extractedCipherText);
} catch (\Chilkat2\Exception $e) {
    // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    echo $e->getMessage(), "\n";
    exit;
}

echo 'Decrypted: ', $decryptedText, "\n";