sodium_pad - PHP code example

Sodium Pad Function in PHP

In PHP, a function is an object-oriented function that performs a single block of code. They are used in many places, such as in class definitions and function calls. Functions can have parameters and can return a value. They are also a powerful tool in coding to make your code more modular and reusable.

Sodium is a modern and opinionated cryptography library that offers secure and sensible defaults. It is a better alternative to the mcrypt and OpenSSL extensions for symmetric encryption. It can also be used for authenticated asymmetric encryption and decryption. For this, the sender and recipient need to have a key pair that they exchange securely. This is usually done using a key exchange protocol or by transmitting the public and private keys with another means. Sodium's crypto_box_seal API does this for you.

The sodium_pad() function adds padding data to a buffer buf whose original size is not a multiple of blocksize. This is useful to hide the message length from observers. It uses the ISO/IEC 7816-4 padding algorithm, which is more resistant to some classes of attacks than other standard padding algorithms.

First, the sender (Alice in this example) creates a key pair by combining her public and private keys. This can be done by concatenating them or by using the sodium_crypto_box_keypair_from_secretkey_and_publickey function. Then, a nonce is generated to be added to each encrypted message. This can be done by generating random numbers or by using the built-in sodium_crypto_box_nonce_generator function.

sodium_pad example

    public static function pad($unpadded, $blockSize, $dontFallback = false)
    {
        /* Type checks: */
        ParagonIE_Sodium_Core_Util::declareScalarType($unpadded, 'string', 1);
        ParagonIE_Sodium_Core_Util::declareScalarType($blockSize, 'int', 2);

        $unpadded = (string) $unpadded;
        $blockSize = (int) $blockSize;

        if (self::useNewSodiumAPI() && !$dontFallback) {
            return (string) sodium_pad($unpadded, $blockSize);
        }

        if ($blockSize <= 0) {
            throw new SodiumException(
                'block size cannot be less than 1'
            );
        }
        $unpadded_len = ParagonIE_Sodium_Core_Util::strlen($unpadded);
        $xpadlen = ($blockSize - 1);
        if (($blockSize & ($blockSize - 1)) === 0) {
            $xpadlen -= $unpadded_len & ($blockSize - 1);
        }

throw EncryptionException::forNeedsStarterKey();
        }

        // create a nonce for this operation         $nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCEBYTES); // 24 bytes
        // add padding before we encrypt the data         if ($this->blockSize <= 0) {
            throw EncryptionException::forEncryptionFailed();
        }

        $data = sodium_pad($data, $this->blockSize);

        // encrypt message and combine with nonce         $ciphertext = $nonce . sodium_crypto_secretbox($data, $nonce, $this->key);

        // cleanup buffers         sodium_memzero($data);
        sodium_memzero($this->key);

        return $ciphertext;
    }