ctx.cat Security Model

ctx.cat private shares are zero-knowledge by default: content and metadata are encrypted before upload, and decrypt keys remain in URL fragments.

Hosted ctx.cat does not sign plaintext user content. CTX_CAT_ENABLE_REMOTE_SIGNING defaults to disabled, so /signing/sign is only for local, self-hosted, or explicitly trusted deployments.

Author signatures should be created by local clients such as ctxcat or ctxcat-mcp. Server provenance receipts cover hashes only: signature envelope version, content hash, metadata hash, public key fingerprint, GitHub username claim, author signature timestamp, and backend receipt timestamp.

Private owner URLs use #key=<decryptKey>&owner=<ownerCapability>. Legacy reader URLs using #<decryptKey> still load. The owner capability authorizes encrypted edits, deletion, expiration changes, and owner-marked encrypted comments.