PHP Extension

AEAD AES 128-bit GCM

See more Encryption Examples

Demonstrates AES encryption using the Galois/Counter Mode (GCM). GCM is an authenticated encryption mode with "additional data" (often referred to as AEAD). GCM is a cipher mode that can be applied to any symmetric encryption algorithm with a 16-byte block size, such as AES and Twofish. In GCM mode, the block encryption algorithm is transformed into a stream encryption algorithm, and therefore no padding occurs (and the PaddingScheme property does not apply). The "additional data" (known as the AAD) does not get encrypted but plays a role in the computation of the resulting "authenticated tag". PHP Extension

<?php

include("chilkat.php");

$success = false;

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

$crypt = new CkCrypt2();

// Set the encryption algorithm to "AES"	
$crypt->put_CryptAlgorithm('aes');

// Indicate that the Galois/Counter Mode (GCM) should be used:
$crypt->put_CipherMode('gcm');

// KeyLength may be 128, 192, 256
$crypt->put_KeyLength(128);

// This is the 128-bit AES secret key (in hex format)
$K = 'feffe9928665731c6d6a8f9467308308';

// This is the 16-byte initialization vector:
$IV = 'cafebabefacedbaddecaf888';

// This is the additional data to be used as input to the GCM AEAD algorithm,
// but is not included in the output.  It plays a role in the computation of the
// resulting authenticated tag.
$AAD = 'feedfacedeadbeeffeedfacedeadbeefabaddad2';

// The plain-text bytes (in hex format) to be encrypted.
$PT = 'd9313225f88406e5a55909c5aff5269a86a7a9531534f7da2e4c303d8a318a721c3c0c95956809532fcf0e2449a6b525b16aedf5aa0de657ba637b39';

// The expected cipher text (in hex format)
$CT = '42831ec2217774244b7221b784d0d49ce3aa212f2c02a4e035c17e2329aca12e21d514b25466931c7d8f6a5aac84aa051ba30b396a0aac973d58e091';

// The expected authenticated tag given the above inputs.
$T = '5bc94fbc3221a5db94fae95ae7121a47';

// Note: The above data are the values for test vector #4 from 
// the PDF document at: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf

// EncodingMode specifies the encoding of the output for
// encryption, and the input for decryption.
// It may be "hex", "url", "base64", or "quoted-printable".
$crypt->put_EncodingMode('hex');

// Set the secret key and IV
$crypt->SetEncodedIV($IV,'hex');
$crypt->SetEncodedKey($K,'hex');

// Set the additional authenticated data (AAD)
$success = $crypt->SetEncodedAad($AAD,'hex');

// For the purpose of duplicating the test vectors, we are using the EncryptEncoded method.
// This method decodes the input string according to the encoding specified by the EncodingMode
// property, which in this case is "hex".  The decoded bytes are encrypted using the mode specified
// by the CipherMode property.  The resulting
// encrypted bytes are encoded (again using the encoding mode specified by EncodingMode),
// and the result is returned.
// <b>Note:</b> The CipherMode property sets the block mode of operation (gcm, cfb, cbc, ofb, ecb, etc.) 
// for any of the Chilkat encryption/decryption methods (such as EncryptBytes, EncryptString, 
// CkEncryptFile, etc.)   Just because GCM mode is demonstrated with EncryptEncoded/DecryptEncoded,
// does not imply that GCM mode is specific to only these methods.
$ctResult = $crypt->encryptEncoded($PT);
if ($crypt->get_LastMethodSuccess() != true) {
    print $crypt->lastErrorText() . "\n";
    exit;
}

// Examine the result.  It should be the same (case insensitive) as our expected result:
print 'computed result: ' . $ctResult . "\n";
print 'expected result: ' . $CT . "\n";

// Examine the authenticated tag. It should be the same (case insensitive) as our expected authenticated tag:
$tResult = $crypt->getEncodedAuthTag('hex');
print 'computed authTag: ' . $tResult . "\n";
print 'expected authTag: ' . $T . "\n";

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

// 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 (case insensitive) to 
// the expected result.
// Note: The return value of SetEncodedAuthTag indicates whether the string passed was a valid
// representation of the encoding specified in the 2nd arg.
$success = $crypt->SetEncodedAuthTag($T,'hex');

// All of our properties (IV, secret key, cipher mode, and AAD) are already set from the code above...

// So let's decrypt CT to and check to see if we get PT.
$ptResult = $crypt->decryptEncoded($CT);
if ($crypt->get_LastMethodSuccess() != true) {
    // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    print $crypt->lastErrorText() . "\n";
    exit;
}

// Examine the decrypted result.  It should be the same as our expected plaintext (case insensitive)
print 'plaintext decrypted: ' . $ptResult . "\n";
print 'plaintext expected:  ' . $PT . "\n";

// Let's intentionally set the expected authenticated tag to an incorrect value. 
// The decrypt operation should fail:
$tInvalid = 'ffaabbbc3221a5db94fae95ae7121a47';

$success = $crypt->SetEncodedAuthTag($tInvalid,'hex');

$ptResult = $crypt->decryptEncoded($CT);
if ($crypt->get_LastMethodSuccess() != true) {
    // Failed.  The resultant authenticated tag did not equal the expected authentication tag.
    print $crypt->lastErrorText() . "\n";
}


?>