# 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=&owner=`. Legacy reader URLs using `#` still load. The owner capability authorizes encrypted edits, deletion, expiration changes, and owner-marked encrypted comments.