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(PHP Extension) AEAD AES 128-bit GCMDemonstrates 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 // The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number. // For example, if using Chilkat v9.5.0.48, then include as shown here: include("chilkat_9_5_0.php"); // 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"; } ?> |
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