PrivateBin is a self-hosted, zero-knowledge pastebin web application. The PHP backend (Controller, Model, Data) handles paste/comment lifecycle, expiration, deletion, traffic limiting, and storage backend selection; the JavaScript frontend performs all encryption/decryption in the browser using AES-256-GCM (WebCrypto) with PBKDF2 key derivation and optional zlib/WASM compression. The server only ever stores ciphertext and metadata, never plaintext. Data flows from browser encryption into a pluggable persistence layer (filesystem, PDO database, Google Cloud Storage, S3), then back to the browser for decryption; JSON API endpoints accept and return encrypted bodies. Architecturally it is a classic server-rendered MVC app with a frontend state layer: index.php bootstraps a Controller, which delegates to Paste/Comment models over an AbstractData storage interface. Views are rendered via PHP templates with Bootstrap 3/5 themes, and the frontend is a vanilla-JS module namespace (PrivateBin) with submodules for encryption, editor, viewer, discussion, attachments, and i18n. The feature set includes expiration times, burn-after-reading, password-protected pastes, discussion threads, file attachments, URL shortening proxies (YOURLS/Shlink), QR codes, dark mode, and multi-language support. Engineering practices are strong for a mature open-source project: PHPUnit tests cover backend behavior, fast-check property tests cover frontend utilities, CI includes CodeQL/Snyk scans, and security hardening (DOMPurify, CSP, SRI hashes, HTTPS guidance) is explicit. Maintenance is active with recent commits and issue triage. Technical drift is moderate: the project retains legacy browser support and old Bootstrap 3/darkstrap assets, still supports PHP 7.4, and ships a monolithic JS file without a build step, but pinned frontend libraries (Bootstrap 5.3.8, Showdown 2.1.0, DOMPurify 3.4.17) are current.