<?php

// Cryptography, key management, credential encryption & token validation
// Split from the former monolithic functions.php


// Function to generate both crypto & URL safe random strings
function randomString(int $length = 16): string {
    $bytes = random_bytes((int) ceil($length * 3 / 4));
    return substr(
        rtrim(strtr(base64_encode($bytes), '+/', '-_'), '='),
        0,
        $length
    );
}

// Generate a cryptographically secure 32-char base32 secret for TOTP
function generateTotpSecret() {
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
    $key = '';
    for ($i = 0; $i < 32; $i++) {
        $key .= $chars[random_int(0, strlen($chars) - 1)];
    }
    return $key;
}

// Called during initial setup
// Encrypts the master key with the user's password
function setupFirstUserSpecificKey($user_password, $site_encryption_master_key) {
    $iv = randomString();
    $salt = randomString();

    //Generate 128-bit (16 byte/char) kdhash of the users password
    $user_password_kdhash = hash_pbkdf2('sha256', $user_password, $salt, 100000, 16);

    //Encrypt the master key with the users kdf'd hash and the IV
    $ciphertext = openssl_encrypt($site_encryption_master_key, 'aes-128-cbc', $user_password_kdhash, 0, $iv);

    return $salt . $iv . $ciphertext;
}

/*
 * For additional users / password changes (and now the API)
 * New Users: Requires the admin setting up their account have a Specific/Session key configured
 * Password Changes: Will use the current info in the session.
*/
function encryptUserSpecificKey($user_password) {
    $iv = randomString();
    $salt = randomString();

    // Get the session info.
    $user_encryption_session_ciphertext = $_SESSION['user_encryption_session_ciphertext'];
    $user_encryption_session_iv = $_SESSION['user_encryption_session_iv'];
    $user_encryption_session_key = $_COOKIE['user_encryption_session_key'];

    // Decrypt the session key to get the master key
    $site_encryption_master_key = openssl_decrypt($user_encryption_session_ciphertext, 'aes-128-cbc', $user_encryption_session_key, 0, $user_encryption_session_iv);

    // Generate 128-bit (16 byte/char) kdhash of the users (new) password
    $user_password_kdhash = hash_pbkdf2('sha256', $user_password, $salt, 100000, 16);

    // Encrypt the master key with the users kdf'd hash and the IV
    $ciphertext = openssl_encrypt($site_encryption_master_key, 'aes-128-cbc', $user_password_kdhash, 0, $iv);

    return $salt . $iv . $ciphertext;
}

// Given a ciphertext (incl. IV) and the user's (or API key) password, returns the site master key
// Ran at login, to facilitate generateUserSessionKey
function decryptUserSpecificKey($user_encryption_ciphertext, $user_password)
{
    //Get the IV, salt and ciphertext
    $salt = substr($user_encryption_ciphertext, 0, 16);
    $iv = substr($user_encryption_ciphertext, 16, 16);
    $ciphertext = substr($user_encryption_ciphertext, 32);

    //Generate 128-bit (16 byte/char) kdhash of the users password
    $user_password_kdhash = hash_pbkdf2('sha256', $user_password, $salt, 100000, 16);

    //Use this hash to get the original/master key
    return openssl_decrypt($ciphertext, 'aes-128-cbc', $user_password_kdhash, 0, $iv);
}

/*
Generates what is probably best described as a session key (ephemeral-ish)
- Allows us to store the master key on the server whilst the user is using the application, without prompting to type their password everytime they want to decrypt a credential
- Ciphertext/IV is stored on the server in the users' session, encryption key is controlled/provided by the user as a cookie
- Only the user can decrypt their session ciphertext to get the master key
- Encryption key never hits the disk in cleartext

*/
function generateUserSessionKey($site_encryption_master_key)
{
    $user_encryption_session_key = randomString();
    $user_encryption_session_iv = randomString();
    $user_encryption_session_ciphertext = openssl_encrypt($site_encryption_master_key, 'aes-128-cbc', $user_encryption_session_key, 0, $user_encryption_session_iv);

    // Store ciphertext in the user's session
    $_SESSION['user_encryption_session_ciphertext'] = $user_encryption_session_ciphertext;
    $_SESSION['user_encryption_session_iv'] = $user_encryption_session_iv;

    // Give the user "their" key as a cookie
    include 'config.php';

    if ($config_https_only) {
        setcookie("user_encryption_session_key", "$user_encryption_session_key", ['path' => '/', 'secure' => true, 'httponly' => true, 'samesite' => 'None']);
    } else {
        setcookie("user_encryption_session_key", $user_encryption_session_key, 0, "/");
        $_SESSION['alert_message'] = "Unencrypted connection flag set: Using non-secure cookies.";
    }
}

// Decrypts an encrypted password (website/asset credentials), returns it as a string
function decryptCredentialEntry($credential_password_ciphertext)
{

    // Split the credential into IV and Ciphertext
    $credential_iv =  substr($credential_password_ciphertext, 0, 16);
    $credential_ciphertext = $salt = substr($credential_password_ciphertext, 16);

    // Get the user session info.
    $user_encryption_session_ciphertext = $_SESSION['user_encryption_session_ciphertext'];
    $user_encryption_session_iv =  $_SESSION['user_encryption_session_iv'];
    $user_encryption_session_key = $_COOKIE['user_encryption_session_key'];

    // Decrypt the session key to get the master key
    $site_encryption_master_key = openssl_decrypt($user_encryption_session_ciphertext, 'aes-128-cbc', $user_encryption_session_key, 0, $user_encryption_session_iv);

    // Decrypt the credential password using the master key
    return openssl_decrypt($credential_ciphertext, 'aes-128-cbc', $site_encryption_master_key, 0, $credential_iv);
}

// Encrypts a website/asset credential password
function encryptCredentialEntry($credential_password_cleartext)
{
    $iv = randomString();

    // Get the user session info.
    $user_encryption_session_ciphertext = $_SESSION['user_encryption_session_ciphertext'];
    $user_encryption_session_iv =  $_SESSION['user_encryption_session_iv'];
    $user_encryption_session_key = $_COOKIE['user_encryption_session_key'];

    //Decrypt the session key to get the master key
    $site_encryption_master_key = openssl_decrypt($user_encryption_session_ciphertext, 'aes-128-cbc', $user_encryption_session_key, 0, $user_encryption_session_iv);

    //Encrypt the website/asset credential using the master key
    $ciphertext = openssl_encrypt($credential_password_cleartext, 'aes-128-cbc', $site_encryption_master_key, 0, $iv);

    return $iv . $ciphertext;
}

function apiDecryptCredentialEntry($credential_ciphertext, $api_key_decrypt_hash, #[\SensitiveParameter]$api_key_decrypt_password)
{
    // Split the Credential entry (username/password) into IV and Ciphertext
    $credential_iv =  substr($credential_ciphertext, 0, 16);
    $credential_ciphertext = $salt = substr($credential_ciphertext, 16);

    // Decrypt the api hash to get the master key
    $site_encryption_master_key = decryptUserSpecificKey($api_key_decrypt_hash, $api_key_decrypt_password);

    // Decrypt the credential password using the master key
    return openssl_decrypt($credential_ciphertext, 'aes-128-cbc', $site_encryption_master_key, 0, $credential_iv);
}

function apiEncryptCredentialEntry(#[\SensitiveParameter]$credential_cleartext, $api_key_decrypt_hash, #[\SensitiveParameter]$api_key_decrypt_password)
{
    $iv = randomString();

    // Decrypt the api hash to get the master key
    $site_encryption_master_key = decryptUserSpecificKey($api_key_decrypt_hash, $api_key_decrypt_password);

    // Encrypt the credential using the master key
    $ciphertext = openssl_encrypt($credential_cleartext, 'aes-128-cbc', $site_encryption_master_key, 0, $iv);

    return $iv . $ciphertext;
}

// Cross-Site Request Forgery check for sensitive functions
// Validates the CSRF token provided matches the one in the users session
function validateCSRFToken($token)
{
    if (hash_equals($token, $_SESSION['csrf_token'])) {
        return true;
    } else {
        $_SESSION['alert_type'] = "warning";
        $_SESSION['alert_message'] = "CSRF token verification failed. Try again, or log out to refresh your token.";
        header("Location: index.php");
        exit();
    }
}

function validateWhitelabelKey($key)
{
    $public_key = "-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAr0k+4ZJudkdGMCFLx5b9
H/sOozvWphFJsjVIF0vPVx9J0bTdml65UdS+32JagIHfPtEUTohaMnI3IAxxCDzl
655qmtjL7RHHdx9UMIKCmtAZOtd2u6rEyZH7vB7cKA49ysKGIaQSGwTQc8DCgsrK
uxRuX04xq9T7T+zuzROw3Y9WjFy9RwrONqLuG8LqO0j7bk5LKYeLAV7u3E/QiqNx
lEljN2UVJ3FZ/LkXeg8ORkV+IHs/toRIfPs/4VQnjEwk5BU6DX2STOvbeZnTqwP3
zgjRYR/zGN5l+az6RB3+0mJRdZdv/y2aRkBlwTxx2gOrPbQAco4a/IOmkE3EbHe7
6wIDAQAP
-----END PUBLIC KEY-----";

    if (openssl_public_decrypt(base64_decode($key), $decrypted, $public_key)) {
        $key_info = json_decode($decrypted, true);
        if ($key_info['expires'] > date('Y-m-d H:i:s', strtotime('-7 day'))) {
            return $key_info;
        }
    }

    return false;
}