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function encrypt_decrypt($action, $string) {
$output = false;
$encrypt_method = "AES-256-CBC";
$secret_key = 'This is my secret key';
$secret_iv = 'This is my secret iv';
// hash
$key = hash('sha256', $secret_key);
// iv - encrypt method AES-256-CBC expects 16 bytes - else you will get a warning
$iv = substr(hash('sha256', $secret_iv), 0, 16);
if( $action == 'encrypt' ) {
$output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
$output = base64_encode($output);
else if( $action == 'decrypt' ){
$output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
return $output;
$plain_txt = "This is my plain text";
echo "Plain Text = $plain_txt\n";
$encrypted_txt = encrypt_decrypt('encrypt', $plain_txt);
echo "Encrypted Text = $encrypted_txt\n";
$decrypted_txt = encrypt_decrypt('decrypt', $encrypted_txt);
echo "Decrypted Text = $decrypted_txt\n";
if( $plain_txt === $decrypted_txt ) echo "SUCCESS";
else echo "FAILED";
echo "\n";

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wampum commented Oct 14, 2016

If anybody stumbles across this code sample, it's horribly broken - please don't use it. You will never get interoperability with other implementations.

Amoungst other things, it double Base64 encodes the output and the keys and ivs used are a lower case hex string representation of the sha256 hashes, converted to bits. Line 12 is the obvious first mistake as it's taking 16 hex digits which is in fact 8 bytes.

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