r-zakarya
ec4fa433a9
Alternative to WebDAV, and the base for an Android client. The server never decrypts: it stores and serves opaque bytes, so a compromise yields ciphertext plus size and mtime. GET only for now, with a strong ETag and If-None-Match; PUT answers 405 explicitly so a client fails loudly rather than believing it wrote. A bad token answers 404 like a missing snapshot, so an unauthenticated caller learns nothing. HTTPS is required - the bearer token rides a header on every call.
103 lines
3.8 KiB
PHP
103 lines
3.8 KiB
PHP
<?php
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/**
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* Read-only sync endpoint for the vault snapshot.
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*
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* The snapshot is an OPAQUE encrypted container (pm-encrypted-export-v1):
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* PBKDF2-SHA256 600k + AES-GCM, produced and read by the clients. This script
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* never decrypts anything and never needs to — it stores and serves bytes.
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* A compromised server yields ciphertext plus the metadata below, nothing more.
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*
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* Deliberately read-only for now: GET only. The write path (PUT with If-Match)
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* comes with the two-way client and is refused explicitly rather than silently
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* ignored, so a client that tries it fails loudly instead of believing it wrote.
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*/
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declare(strict_types=1);
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require __DIR__ . '/config.php'; // defines SYNC_TOKEN and SYNC_FILE
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// ---------------------------------------------------------------------------
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// Transport
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// ---------------------------------------------------------------------------
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// The token travels in a header on every request; without TLS it is readable by
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// anyone on the path, and so is the ciphertext. Refuse rather than leak.
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$https = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off')
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|| (($_SERVER['HTTP_X_FORWARDED_PROTO'] ?? '') === 'https')
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|| in_array($_SERVER['REMOTE_ADDR'] ?? '', ['127.0.0.1', '::1'], true);
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if (!$https) {
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http_response_code(403);
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header('Content-Type: application/json');
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echo json_encode(['error' => 'HTTPS required']);
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exit;
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}
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header('Content-Type: application/json');
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// This endpoint is for native clients, never a browser page: no CORS, no cache.
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header('Cache-Control: no-store');
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header('X-Content-Type-Options: nosniff');
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// ---------------------------------------------------------------------------
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// Authentication
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// ---------------------------------------------------------------------------
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/** Bearer token, compared in constant time so a wrong guess leaks no timing. */
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function client_token(): string {
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$h = $_SERVER['HTTP_AUTHORIZATION'] ?? $_SERVER['REDIRECT_HTTP_AUTHORIZATION'] ?? '';
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if (stripos($h, 'Bearer ') === 0) return substr($h, 7);
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return '';
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}
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if (!hash_equals(SYNC_TOKEN, client_token())) {
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// 404, not 401: an unauthenticated caller learns nothing about what lives
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// here — same reasoning as the desktop server's loopback lockdown.
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http_response_code(404);
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echo json_encode(['error' => 'Not found']);
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exit;
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}
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// ---------------------------------------------------------------------------
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// Routing
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// ---------------------------------------------------------------------------
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$method = $_SERVER['REQUEST_METHOD'] ?? 'GET';
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if ($method === 'HEAD' || $method === 'GET') {
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if (!is_file(SYNC_FILE)) {
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// 404 = "no snapshot yet". The desktop client already treats this as
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// "first sync, remote is empty" rather than an error.
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http_response_code(404);
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echo json_encode(['error' => 'No snapshot yet']);
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exit;
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}
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$blob = file_get_contents(SYNC_FILE);
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if ($blob === false) {
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http_response_code(500);
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echo json_encode(['error' => 'Read failed']);
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exit;
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}
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// Strong ETag over the bytes. The write path will require If-Match against
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// it, which is what stops two devices from clobbering each other.
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$etag = '"' . hash('sha256', $blob) . '"';
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header('ETag: ' . $etag);
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header('Last-Modified: ' . gmdate('D, d M Y H:i:s', (int)filemtime(SYNC_FILE)) . ' GMT');
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// Save the round trip when the client already holds this version.
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if (trim($_SERVER['HTTP_IF_NONE_MATCH'] ?? '') === $etag) {
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http_response_code(304);
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exit;
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}
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header('Content-Length: ' . strlen($blob));
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if ($method === 'HEAD') exit;
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echo $blob;
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exit;
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}
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// Everything else — including PUT — is not implemented yet.
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http_response_code(405);
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header('Allow: GET, HEAD');
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echo json_encode(['error' => 'Read-only endpoint']);
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