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(PHP Extension) Generate Encryption KeyDiscusses symmetric encryption key generation techniques for block encryption algorithms such as AES, Blowfish, and Twofish, or for other algorithms such as ChaCha20.
<?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"); // Symmetric encryption algorithms are such that the encryptor and decryptor // share a pre-known secret key. This could be a "single-use" key that is // derived from a secure key exchange algorithm using RSA, ECC, or Diffie-Hellman, // or it could be a password known to both sides, or // it could simply be the binary bytes of the secret key known in advance on both // sides. // A secret key has no structure. It's nothing more than N bytes of data. // It should typically be random data, or bytes that resemble random data such // as the hash of a password. // The number of bytes in the secret key defines the bit-strength of an encryption // algorithm. For example, AES with a 32-byte key is 256-bit AES. Most algorithms // define restrictions on key sizes. For example, AES has 3 choices: 128-bit, 192-bit, // or 256-bit. In the ChaCha20 algorithm, the key size must always be 256-bits (32-bytes). // Both sides (encryptor and decryptor) must be in possession of the same secret key // in order to communicate. Whichever side generates the key, it must somehow // deliver the key to the other side beforehand. Key exchange algorithms, such as RSA, ECC, // and Diffie-Hellman define secure ways of exchanging symmetric encryption keys. // They do so using asymmetric encryption algorithms (public/private keys). It is not // required to use a key exchange algorithm to achieve the goal of having both sides // in possession of the same secret key. A long-living secret key could be exchanged // via any secure out-of-band means. For example, exchanging the information over a secure // TLS (HTTPS) or SSH connection... // This example assumes the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. $crypt = new CkCrypt2(); $crypt->put_CryptAlgorithm('aes'); $crypt->put_KeyLength(256); // Generate a 32-byte random secret key, // and use it in the crypt object. $prng = new CkPrng(); $secretKeyHex = $prng->genRandom(32,'hex'); // It is important that the number of bytes in the secret key // matches the value specified in the KeyLength property (above). $crypt->SetEncodedKey($secretKeyHex,'hex'); print 'randomly generated key: ' . $secretKeyHex . "\n"; // Alternatively, a password could be hashed using a hash algorithm // the results in the desired key length. Our desired key length // in this case is 32 bytes, so we wouldn't want MD5 (16 bytes), // nor would we want to use SHA-1 (20 bytes). SHA256 would be the // hash of choice because it results in 32-bytes of random-looking // key material. $crypt->put_HashAlgorithm('SHA256'); $crypt->put_EncodingMode('hex'); $secretKeyHex = $crypt->hashStringENC('mypassword'); $crypt->SetEncodedKey($secretKeyHex,'hex'); print 'password-based key: ' . $secretKeyHex . "\n"; ?> |
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