SecretBox

Authenticated encryption for secrets at rest. SecretBox (includes/SecretBox.php) is a general-purpose core helper with no OAuth or database dependency — use it anywhere the platform must persist a credential without storing plaintext: OAuth client secrets and refresh tokens, IMAP passwords, any stored API secret.

It turns a plaintext string into a self-describing, tamper-evident blob and back. The first caller is the OAuth core (see OAuth2 Core), but nothing about SecretBox is OAuth-specific.

API

$box = new SecretBox();                  // throws if secret_box_key is missing/malformed
$blob  = $box->encrypt($plaintext);      // -> "v1.<algo>.<nonce>.<ciphertext>"
$plain = $box->decrypt($blob);           // throws on tamper / wrong key / malformed blob

SecretBox::looksEncrypted($value);       // static bool: is this a SecretBox blob vs. legacy plaintext?

  • __construct() — reads the key (below) and validates it's exactly 32 bytes. If absent or the wrong length it throws — SecretBox fails closed and never silently stores plaintext.
  • encrypt($plaintext): string — fresh random nonce per call, so encrypting the same value twice yields different blobs.
  • decrypt($blob): string — verifies the authentication tag; any tampering, wrong key, or malformed input throws rather than returning garbage.
  • looksEncrypted($value): bool (static) — cheap prefix check so a caller can tell a blob from a pre-existing plaintext value and migrate lazily, without a separate flag column.

Blob format

v1.<algo>.<nonce>.<ciphertext>

Base64url parts. <algo> is sodium (libsodium crypto_secretbox, preferred when the extension is present) or aesgcm (OpenSSL AES-256-GCM fallback, with the 16-byte GCM auth tag prepended to the ciphertext). The algorithm travels inside the value, so decrypt() never has to guess; the v1 prefix leaves room to rotate algorithms later without breaking existing blobs.

The key — secret_box_key

SecretBox reads a 32-byte, base64-encoded key from secret_box_key in config/Globalvars_site.php. It is bootstrap-level infrastructure config (alongside the DB credentials), not a stg_settings value, because it must be available before the database and must never live in the database it protects.

  • On install, _site_init.sh generates it per environment.
  • For an existing site, add it manually:
  // in config/Globalvars_site.php
  $this->settings['secret_box_key'] = '<base64_encode(random_bytes(32)) output>';

Generate the value without echoing it into a shared shell history/log:

  php -r 'echo base64_encode(random_bytes(32)), "\n";'

If the key is absent, the constructor throws (fail closed). *Changing or losing the key makes every value encrypted with it permanently undecryptable — treat it like the DB password: per-environment, backed up, never rotated casually.

Usage pattern

Encrypt before persisting, decrypt on read, and use looksEncrypted() to migrate any pre-existing plaintext in place:

// write
$setting->set('stg_value', (new SecretBox())->encrypt($plaintext));

// read (tolerating a legacy plaintext value)
$stored = $settings->get_setting('my_secret');
$plain  = SecretBox::looksEncrypted($stored) ? (new SecretBox())->decrypt($stored) : $stored;

Guarantees

  • Authenticated — tampering is detected on decrypt, never silently accepted.
  • Randomized — a fresh nonce per call; identical plaintexts produce distinct blobs.
  • Fail-closed — no key, no operation; never a plaintext fallback.
  • Quiet — never logs or echoes plaintext.
  • Self-contained — no DB dependency; safe to use from any layer.

The per-user asymmetric layer above this

SecretBox is one symmetric key the server holds for its own secrets. SealedBox (includes/SealedBox.php) is the asymmetric sibling one layer up: a per-user* X25519 keypair whose secret half the server never holds at rest, behind the Sealed Vault's unlock window. Reach for SecretBox for server-held credentials (OAuth secrets, IMAP passwords); reach for the vault for user content the server should only read while the user has proven presence. For client-custody scopes — the password manager and Drive encryption — even the vault's secret key is unwrapped only in the browser: SecretBox and server-side SealedBox are never in that path, because the server is never meant to decrypt that content at all. A Drive file key is generated, wrapped, and opened entirely client-side; the server stores only opaque ciphertext and wrapped keys.

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