CryptPad

CryptPad is the encrypted-in-browser real-time collaborative office suite — an open-source platform offering rich documents, spreadsheets, presentations, kanban boards, and forms where all encryption happens client-side and the server stores only ciphertext. Listed at Grade A because CryptPad occupies a unique structural slot: real-time collaboration (people typing in the same doc simultaneously, seeing each other's cursors, exchanging comments) with zero-knowledge encryption — combining the convenience of Google Docs/Notion with a privacy posture the cloud office suites can't match.

Background. CryptPad was developed by XWiki SAS (a French open-source software company) and is now maintained by the CryptPad team within XWiki. Active development since 2014 (originally as a single-pad CodeMirror demo, evolved into the full office suite). Open source under AGPLv3; codebase at github.com/xwiki-labs/cryptpad. The public hosted instance at cryptpad.fr is free and reasonably scaled; self-host is well-supported with documented Docker deployment + production-grade configuration guides. Funding mix: French government IT body DINUM (Direction Interministérielle du Numérique), NLnet grants, NGI Zero (Next Generation Internet from the European Commission), plus paid features on the hosted plans. The funding model means CryptPad has long-term sustainability through public-interest channels rather than VC pressure.

What you trust. Client-side encryption — the server stores ciphertext; encryption keys live in the URL fragment (the part after `#` which browsers never send to servers). When you share a CryptPad URL, the key travels in the URL fragment and the server never sees it. Open-source codebase — every component is auditable. Zero-knowledge architecture — CryptPad operator (or self-hosted operator) can't read your document content even if they wanted to. Real-time collaboration via CRDTs — Conflict-free Replicated Data Types are the cryptographic-friendly primitive that lets multiple editors converge on the same encrypted document state. No tracking — CryptPad's privacy policy and codebase are explicit about not tracking users; no analytics SDK, no user-identifying telemetry. Tor-friendly — works on Tor Browser without aggressive anti-Tor measures. What you don't trust: URL fragments — your encryption key is in the URL; if you share the URL with someone, you've shared the key. Anyone with the URL can read the document. Treat URL sharing as the access-control mechanism (which it is, by design). Server metadata — the server sees connection timing, document size, edit frequency (encrypted but visible as encrypted blobs). For high-threat scenarios, self-host. Browser-level trust — encryption happens in JavaScript running in your browser; a compromised browser or malicious extension can read documents at the point where the JS handles plaintext.

Operational specs. Platform: web application — works in any modern browser; no native apps. Application types: Rich text documents (collaborative editor with formatting, similar to Google Docs), Sheets (spreadsheets, similar to Google Sheets), Presentations (slide deck), Code (collaborative code editor with syntax highlighting for ~50 languages), Markdown, Whiteboard (drawing/sketching), Kanban (project management), Forms / Polls (surveys and shared decision-making), Drive (file storage / organising). Registered vs anonymous use: anonymous use is fully supported (just open cryptpad.fr and start a document); registered use unlocks persistent profile + drive storage + premium quotas. Storage limits: cryptpad.fr free tier ~1GB per account; paid tiers up to 50GB+; self-host is limited only by your server's disk. Tor compatibility: works on Tor Browser with normal settings (some real-time features may degrade slightly on slower Tor circuits). Self-host deployment: documented Docker setup, plus production guidance for nginx reverse proxy, TLS, and storage configuration. Federation: not in the Matrix sense — but CryptPad documents can be shared between separately-operated CryptPad instances if both sides have the URL.

Philosophy. CryptPad's editorial differentiator is the real-time-collaboration-with-zero-knowledge model. Standard Notes is great for note-taking solo; KeePassXC for password storage; Element/Matrix for chat. The "collaborative office suite" slot is dominated by Google Docs (no privacy posture), Microsoft 365 (same), and Notion (some encryption but proprietary, US-cloud). CryptPad says: collaboration is a legitimate use case; encryption shouldn't be impossible just because multiple people edit together. The technical innovation is making CRDTs work in an end-to-end-encrypted setting. The trade-off: URL-fragment-as-key is a different access-control model than account-based sharing (you share via URL, not by inviting a username), which has its own UX implications (forwarded URLs grant access; revoked access requires regenerating the URL).

Grade rationale. Grade A reflects: open-source AGPLv3 codebase; 11+ years of operational continuity (since 2014); independent security audits by Cure53 and ROS (Radically Open Security); zero-knowledge architecture with client-side encryption; real-time collaboration via CRDTs; multiple application types (docs, sheets, slides, code, drive, kanban, etc.); public-interest funding (DINUM, NLnet, NGI Zero — no VC dependence); self-host fallback well-documented; Tor-friendly; no tracking, no analytics SDK; named operator (XWiki SAS / French company with public identity); cross-listed in web3privacy peer directory. Last verified 2026-05-13.

Useful when. You want real-time collaboration (multiple people typing in the same document simultaneously) with zero-knowledge encryption — CryptPad is the canonical pick. You're an organisation or activist group that needs shared document workflows but doesn't want to trust Google or Microsoft with the content. You want to self-host an office suite — CryptPad is one of the few open-source real-time collaborative options with documented deployment. You want shared decision-making tools (polls, forms, kanban) without account-tied vendor lock-in. You're anonymously collaborating with a contact — you can both open cryptpad.fr without accounts, generate a document, share the URL, edit together. You're an education or research team handling sensitive content that has collaboration needs. You're building privacy-respecting infrastructure and need a collaborative-doc-equivalent of Google Docs as part of the stack.

Caveats. URL-as-access-token model — anyone with the URL can read/edit (depending on URL type); treat URL forwarding as access grants. For revoking access, regenerate the URL and update collaborators. Server-side metadata visibility — encrypted blobs are encrypted, but the server sees connection timing, document edit cadence, and document sizes. For high-threat use, self-host. Browser-trust ceiling — encryption happens in browser JavaScript; a compromised browser (or malicious extension) can read plaintext at the point of decryption. Use hardened browsers (Tor Browser, Mullvad Browser) for high-threat documents. Real-time sync over Tor can be slower — Tor's latency makes typing-with-multiple-collaborators feel noticeable; for asynchronous editing this is fine. No native mobile apps — web only at this writing; mobile users use the web version with appropriate browser. Self-host has operational overhead — Docker is easy; production setup (TLS, persistence, scaling) requires some sysadmin skill. Free tier on cryptpad.fr has storage caps — 1GB on the free tier; for heavier use, pay or self-host. Recovery without account is limited — anonymous use loses documents if the URL is lost; registered use offers Drive persistence; self-host gives you full control. Multi-language UI is comprehensive but not all features are translated — the core UI is well-translated; some advanced features and documentation lag the English version. Doesn't replace Office's advanced features — for users who depend on specific Microsoft Office features (advanced spreadsheet macros, complex slide animations, integrated Outlook-grade workflows), CryptPad's feature set is structurally less feature-rich. For typical collaborative document use (text, sheets, slides, kanban, polls, forms), CryptPad is sufficient.