Gravity Forms Description

gforms-encrypt.php

//https://www.gravityhelp.com/documentation/article/gform_save_field_value/
add_filter( 'gform_save_field_value', 'jb_encrypt_value', 10, 4 );
function jb_encrypt_value( $value, $lead, $field, $form ) {

    if($field->cssClass == 'secure'){
	$encrypted = GFCommon::encrypt( $value );
	return $encrypted;
    }

    return $value;
}

//https://www.gravityhelp.com/documentation/article/gform_get_input_value/
add_filter( 'gform_get_input_value', 'jb_decrypt_value', 10, 4 );
function jb_decrypt_value( $value, $entry, $field, $input_id ) {

    if($field->cssClass == 'secure'){
	$decrypted = GFCommon::decrypt( $value );
	return $decrypted;
    }

    return $value;
}