pithos/DESIGN-hosted.md

Pithos "On Silent Mode": hosted s3d with your own Sia account

Status: built 2026-10-04 (Pithos 0.3.7, hosted/), not deployed. Exercised end to end against a mock indexer; not yet against sia.storage. Scope: bring-your-own-account only. Paid storage is Hestia, a separate product (see "Later").

What the user gets

Pithos gains a choice under Settings: On this computer (today, unchanged, still the default) or On Silent Mode. The interface is the same in both modes: drives, browser, viewer, Users & keys, share links. Hosted mode adds:

• nothing to keep running: apps, S3 clients and share links work with the PC off
• the same drives from any device, at https://s3.silentmode.st
• per-folder public access and per-person rights (read / add / edit), which a bare s3d cannot do

The storage stays the user's own sia.storage account, so it costs Silent Mode no siacoins. What we pay for is VPS memory and disk and all hosted traffic.

Decisions taken

Model	Bring your own sia.storage account. Silent Mode plans are out of scope here.
Indexer	sia.storage (the user's own account). No Silent Mode indexd.
Encryption	Private files are encrypted on the user's machine before upload, file names included. Anything public or shared by link is stored readable.
Anti-Sybil	A hosted slot needs a BNS name or a small refundable BCH deposit, plus a per-IP sign-up limit. With BYO accounts this protects RAM and bandwidth, not storage.

Why one s3d per user

An s3d process is bound to one Sia account: its connection key, users, keys, buckets and upload buffer all live in its data folder (s3d.db). That is also why Pithos's account switch works by moving the folder. So the server runs one s3d per hosted user. Each one gets its own data folder, loopback-only ports, and admin password.

• Your recovery phrase never leaves your PC. You connect locally as today. Pithos then uploads the connected data folder, which carries only the connection key for this one app. The connection uses one of sia.storage's 3 app slots per account.
• The server holds that connection key and so could read anything s3d stores. This is why private files get the extra client-side layer below.
• Idle s3d processes are stopped. A user's s3d starts on the first request (a few seconds) and stops after 30 min with no requests and nothing pending. Before it stops, leftovers are flushed to Sia (the auto-flush setting, forced on in hosted mode).

Server: pithos-hosted on the VPS

A Node service in Pithos/server-hosted/ that reuses core/. It does not duplicate it.

1. Supervisor. /var/lib/pithos-hosted/<uid>/ holds s3d.yml and the data. Ports come from a pool and are bound to 127.0.0.1 only. A per-user diskUsageLimit keeps upload buffers bounded, and there's a cap on how many s3d run at once (LRU stop). systemd unit, nginx TLS, deployed from the repo.
2. Per-user Pithos. Each user gets one createPithos() instance with hostName: 'hosted', so the exact same /api/* surface is served. Routes that make no sense on a server are refused in hosted mode: binary install, address settings, login pty, open-external, account switch/restore.
3. Sign-in. The identity is a key from the Theseus vault (new derive path pithos/hosted-identity/v1; the existing pithos/sia-recovery/v1 and pithos/credentials/v1 stay untouched). Challenge → signature → session token. The desktop and web hosts use a local identity file that can be exported and imported. Sign-up runs the anti-Sybil check: a BNS name owned by the key's address, or a deposit tx.
4. Gateway S3 keys. Hosted s3d is never exposed. The gateway mints its own SigV4 keys, verifies them itself (core/s3.js already signs, so verification mirrors it) and re-signs to the user's s3d. That's what makes the rules below enforceable, and it lets rclone, aws-cli and the like keep working.
5. Meters. Monthly download bytes per user, with a cap (proposed 50 GB per month, then throttled) and per-IP sign-up limits.

Per-folder access and rights

Rules are stored per user: { drive, prefix, who, rights, expires }.

• who: public, a link token, or a person (BNS name or wallet address, who signs in like any user)
• rights: read (GET, HEAD, list), add (create new keys only: PUT with If-None-Match / existence check, no DELETE, no overwrite), edit (PUT and DELETE)

Every request through the gateway, whether S3 API, /api, public URL https://s3.silentmode.st/p/<user>/<drive>/<path> or share link, is matched against the longest prefix rule. List results are filtered to what the caller may see. The owner always has full rights. This is what s3d alone can't do: its bucket policy is whole-bucket public read only.

Encrypted folders can be shared with a person only once key sharing exists (the folder key wrapped to the grantee's public key; v2). Until then, the UI offers to share those folders as readable copies, and says so.

Client-side encryption

The encryption happens in the local Pithos core. In hosted mode it acts as an encrypting forwarder between the unchanged UI and the gateway, so plaintext and keys never leave the PC.

• Key: HKDF from the vault, path pithos/hosted-encryption/v1, one key per drive (HKDF(master, drive id)).
• Bodies: AES-256-GCM in 1 MiB chunks, each with its own nonce and the chunk index authenticated. Range reads and streaming keep working.
• Names: encrypted per path segment with AES-SIV (deterministic), so folders still list and the server sees no file names (decided: in v1). Sizes, folder depth and timestamps remain visible.
• Making an encrypted folder public or shared by link re-uploads it decrypted, after a confirmation that says what becomes readable.
• Losing the vault means losing the files. Same as the rest of Silent Mode.

Moving between local and hosted

No file is re-uploaded to Sia. Only s3d's metadata folder moves.

Local → hosted: flush everything to Sia, stop local s3d, upload the data folder (TLS, authenticated), then the gateway starts s3d on it and checks the bucket list. The local copy is archived like an account switch, never deleted. Pithos refuses to run a local s3d on a data folder that's live on the server: two s3d writing one account's metadata would diverge. Existing files stay unencrypted. Pithos offers "Encrypt existing private files", a background re-upload, and lists what is still readable until that's done.

Hosted → local: the gateway flushes and stops, Pithos downloads the folder, starts local s3d on it, and the gateway deletes its copy after the local start succeeds. Encrypted files remain encrypted. Pithos decrypts them on read in both modes.

s3d must be the same pinned version on both sides (today 0.2.0). The migration checks this before it starts.

Build order

Step	What	State
1	Supervisor + per-user createPithos + sign-in/sessions + anti-Sybil check	done
2	Pithos client mode switch, forwarder, hosted status in Overview	done
3	Migration both ways, live-elsewhere lock	done
4	Encryption (bodies and names)	done
5	Gateway SigV4 keys, access rules, public URLs, share links	done
6	Meters, limits, docs	done; deploy (DNS for s3.silentmode.st, nginx, systemd) waiting

One change from the plan: "rights for a person" are S3 keys the owner mints for one folder (read, add-only or edit), not a second sign-in by the other person's wallet. Keys work with every S3 client and need no account on the other side; a wallet-bound variant can come with encrypted sharing (v2).

Pithos changes ship as extension OTA versions, never a Theseus release.

Open points

• Host: the current VPS is at 79% disk. Upload buffers need headroom, so this may need a separate box. Measure s3d memory per process first.
• Download cap per user (proposed 50 GB per month).

Later: Hestia

Selling storage is a separate product: Hestia, enterprise software with which an operator sets their own storage limits, prices and plans and monetizes storage (Silent Mode's own 500 MB free web hosting and paid tiers would be one deployment of it). It can reuse pieces built here: the per-account s3d supervisor, the gateway's SigV4 and rule enforcement, client-side encryption. Pithos stays free of quotas and billing.