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(PHP Extension) AES GCM Encrypt and Decrypt a FileSee more Encryption ExamplesDemonstrates how to AES GCM encrypt and decrypt a file.
<?php include("chilkat.php"); // Use "chilkat_9_5_0.php" for versions of Chilkat < 10.0.0 // 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(256); // This is the 256-bit AES secret key (in hex format) $K = '000102030405060708090A0B0C0D0E0F000102030405060708090A0B0C0D0E0F'; // This is the 16-byte initialization vector (in hex format) $IV = '000102030405060708090A0B0C0D0E0F'; // This is the OPTIONAL additional data (in hex format) 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'; // 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'); // Encrypt a file. $inFile = 'qa_data/hamlet.xml'; $outFile = 'c:/temp/qa_output/hamlet_aes_gcm.enc'; $success = $crypt->CkEncryptFile($inFile,$outFile); if ($success == false) { print $crypt->lastErrorText() . "\n"; exit; } // Get the authentication tag in hex format $authTag = $crypt->getEncodedAuthTag('hex'); print 'authentication tag = ' . $authTag . "\n"; // Decrypt.. // Before decrypting, you must provide the expected authentication tag. // The decrypt will fail if the resulting authentication tag computed while decrypting is not equal to the // expected authentication tag. $crypt->SetEncodedAuthTag($authTag,'hex'); $inFile = $outFile; $outFile = 'c:/temp/qa_output/hamlet_restored.xml'; $success = $crypt->CkDecryptFile($inFile,$outFile); if ($success == false) { print $crypt->lastErrorText() . "\n"; exit; } print 'Success.' . "\n"; // -------------------------------------------------------------------------------------------- // About AES-GCM: // AES-GCM (Advanced Encryption Standard - Galois/Counter Mode) is a widely-used // encryption mode that provides both confidentiality (encryption) and // integrity/authentication (data integrity verification) in one operation. It is // commonly used in secure communications due to its efficiency and strong security // properties. // // Key Concepts: // // AES (Advanced Encryption Standard): // // AES is a symmetric encryption algorithm, meaning the same key is used // for both encryption and decryption. // // It operates on fixed-size blocks of data (128 bits) using key sizes of // 128, 192, or 256 bits. // // In AES-GCM, AES is used to perform the actual data encryption. // // GCM (Galois/Counter Mode): // // Counter Mode (CTR): GCM uses counter mode for encryption. In this mode, // a nonce (or initialization vector, IV) and a counter are combined and encrypted // with AES. The result is XORed with the plaintext to produce the ciphertext. // // Galois Mode (GMAC): GCM also includes an authentication mechanism based // on a Galois field. It generates an authentication tag, which ensures the // integrity of both the ciphertext and any additional data (called AAD - // Additional Authenticated Data). This tag is verified during decryption to ensure // that the data hasn't been tampered with. // // Key Features: // // Confidentiality (Encryption): // // The plaintext is encrypted using AES in counter mode. Each block of // plaintext is XORed with the output of AES applied to a combination of the IV and // an incremented counter. // // Integrity (Authentication): // // In addition to encryption, GCM provides authentication for both the // encrypted data (ciphertext) and any Additional Authenticated Data (AAD), such as // headers or metadata that need to be protected but not encrypted. // // The authentication tag is generated using a Galois field multiplication // of the ciphertext and AAD. This ensures that any changes to the encrypted // message or the AAD will be detected during decryption. // // Key Components: // // - Plaintext: The data you want to encrypt. // - Ciphertext: The encrypted data. // - Key: A symmetric key used for both encryption and decryption. // - Nonce/IV: A unique value used for each encryption to ensure security. It is not secret but should never be reused with the same key. // - AAD (Additional Authenticated Data): Optional data that is not encrypted but needs to be authenticated (e.g., headers). // - Authentication Tag: A tag generated to verify the integrity and authenticity of the ciphertext and AAD ?> |
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