AES-256-CBC: A Breakdown

AES-256-CBC stands for Advanced Encryption Standard with a 256-bit key in Cipher Block Chaining mode.

AES (Advanced Encryption Standard)

• A symmetric block cipher, meaning the same key is used for both encryption and decryption.  
• Widely adopted as a strong encryption standard.  
• Offers different key sizes: 128, 192, and 256 bits.

256-bit key

• Refers to the key length used in the AES algorithm.  
• – A 256-bit key is considered extremely secure, making it difficult to crack even with powerful computers.

CBC (Cipher Block Chaining)

• An operating mode for block ciphers like AES.  
• Ensures that even if the same plaintext block appears multiple times, the ciphertext will be different.  
• Achieves this by XORing the previous ciphertext block with the current plaintext block before encryption. 

How it works?

• Data is divided into fixed-size blocks (usually 128 bits for AES).  
• The first block is encrypted with the key.
• The encrypted block is XORed with the next plaintext block before encryption.
• This process continues for all blocks.

Let’s Understand this with function

    public static function encrypt_data($data, $key)
    {
        $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
        $encrypted_data = openssl_encrypt($data, 'aes-256-cbc', $key, 0, $iv);
        return base64_encode($encrypted_data . '::' . $iv);
    }

    public static function decrypt_data($data, $key)
    {
        list($encrypted_data, $iv) = explode('::', base64_decode($data), 2);
        return openssl_decrypt($encrypted_data, 'aes-256-cbc', $key, 0, $iv);
    }

encrypt_data Function

This function encrypts data using the AES-256-CBC encryption algorithm.

Breakdown:

1. Generate an Initialization Vector (IV):
   • openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc')) generates a random IV with the appropriate length for AES-256-CBC. The IV is essential for the security of the encryption process.
2. Encrypt the data:
   • openssl_encrypt($data, 'aes-256-cbc', $key, 0, $iv) encrypts the provided $data using the AES-256-CBC algorithm with the given $key and the generated IV.
3. Combine encrypted data and IV:
   • Concatenates the encrypted data and the IV with a ‘::’ separator.
4. Base64 encode:
   • Encodes the combined data into a base64 string for easier handling and transmission.

Return value:

• The function returns the base64 encoded string containing the encrypted data and the IV.

decrypt_data Function

This function decrypts data previously encrypted using the encrypt_data function.

Breakdown:

1. Decode the data:
   • base64_decode($data) decodes the base64 encoded string back to its original format.
2. Separate encrypted data and IV:
   • explode('::', ...) splits the decoded data into two parts: the encrypted data and the IV, using ‘::’ as the separator.
3. Decrypt the data:
   • openssl_decrypt($encrypted_data, 'aes-256-cbc', $key, 0, $iv) decrypts the encrypted data using the provided $key and the extracted IV.

Return value:

• The function returns the decrypted data.