AES Encrypt & Decrypt

Advanced Encryption Standard, where we use AES-256 to encrypt the data with Cipher. Encrypt & Decrypt approach taken is 'Cipher Block Chaining' method 'AES-256-CBC'.

AES Encrypt

• We would have the 'Secret' stored in a file which is other than the web root.

 $key = hash('sha256', $secret, true);

• Hash the 'Secret' with sha256, this gives you the 'Key' which will be used to openssl encrypt.
• And Generate the pseudo random bytes as 'IV', so that it would be used during encryption and also be attached to the encrypted data.

 $iv = openssl_random_pseudo_bytes(16);

• Now encrypt the 'String' with openssl encrypt by passing the 'AES-256-CBC' method, 'Key' and 'IV'

 $ciphertext = openssl_encrypt($plaintext, $method, $key, OPENSSL_RAW_DATA, $iv);

• 'openssl_encrypt' will Encrypt given data with given method and key, returns a raw or base64 encoded string.
• 'Hash' the returned 'Cipher' text with sha256 hmac method

 $hash = hash_hmac('sha256', $ciphertext, $key, true);

• Now concatenate the 'IV' & 'Hash' & 'Cipher' and store in the DB as the encrypted value.

AES Decrypt

• Hash the 'Secret' with sha256, this gives you the 'Key' which will be used to openssl encrypt.

 $key = hash('sha256', $password, true);

• Explode the concatenated string to 'IV' & 'Hash' & 'Cipher'

 $iv = substr($ivHashCiphertext, 0, 16);$hash = substr($ivHashCiphertext, 16, 32);$ciphertext = substr($ivHashCiphertext, 48);

• 'openssl_decrypt' will take a raw or base64 encoded string and decrypts it using a given method and key.
• Now decrypt the 'Cipher' with 'AES-256-CBC' method, 'Key' and 'IV'

 openssl_decrypt($ciphertext, $method, $key, OPENSSL_RAW_DATA, $iv);

• Return the decrypted 'String'. it is ok, or do i need to change it to excel.

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