| 1 | package main |
| 2 | |
| 3 | // Sealed instance branding under the link-carried branding key |
| 4 | // (docs/no-plaintext.md). Branding — group name, description, admin identity, |
| 5 | // the server avatar and its alt — must render on surfaces where no member key |
| 6 | // exists yet (join cards, native add-chat, the home save card). Every one of |
| 7 | // those surfaces is reached via a link, so branding can be sealed under a key |
| 8 | // B that rides the link #fragment (never sent to the server): clients derive |
| 9 | // an AES key from B (PBKDF2, see crypto.js deriveBrandingKey) and open one |
| 10 | // blob. Members bootstrap B from a copy sealed under the instance key, so |
| 11 | // nobody needs to re-visit a link. |
| 12 | // |
| 13 | // The server's role here is storage and gating only: it never sees B, never |
| 14 | // derives, never opens. All ciphertext below is produced client-side by an |
| 15 | // admin who holds both admin authority and the instance key. Sealing is |
| 16 | // opt-in per instance and reversible (the client supplies the plaintext back |
| 17 | // on unseal — the server cannot). |
| 18 | // |
| 19 | // Honest scope (also in the doc): B is short and the ciphertext sits on this |
| 20 | // very server, so sealing defeats bulk exposure of a leaked DB or bucket, not |
| 21 | // a targeted brute-force by the operator. Member content is never under B. |
| 22 | |
| 23 | import ( |
| 24 | "encoding/json" |
| 25 | "net/http" |
| 26 | "time" |
| 27 | ) |
| 28 | |
| 29 | // sealedAvatarMime marks instance_avatar bytes as branding-key ciphertext |
| 30 | // (the base64url iv||ct string, stored as bytes). Clients that see this |
| 31 | // content type fetch the body as text and decrypt with the branding key. |
| 32 | const sealedAvatarMime = "application/vnd.lchat.sealed" |
| 33 | |
| 34 | func (db *DB) brandingSealed() bool { |
| 35 | v, _, _ := db.getConfig("branding_sealed") |
| 36 | return v == "1" |
| 37 | } |
| 38 | |
| 39 | // sealBranding stores the client-sealed branding set and clears every |
| 40 | // plaintext counterpart in the same request, flipping the instance to sealed |
| 41 | // mode. Idempotent: re-posting (a rename, a new photo) overwrites the blobs. |
| 42 | func (s *Server) sealBranding(w http.ResponseWriter, r *http.Request) { |
| 43 | if !s.requireAdmin(w, r) { |
| 44 | return |
| 45 | } |
| 46 | var body struct { |
| 47 | // AES-GCM over {name, description, admin_name, admin_email, |
| 48 | // avatar_alt, avatar_mime} under the B-derived key. |
| 49 | BrandingBlob string `json:"branding_blob"` |
| 50 | // PBKDF2 salt for deriving from B — random, not secret. |
| 51 | BrandingSalt string `json:"branding_salt"` |
| 52 | // B sealed under the instance key, for member bootstrap. |
| 53 | BrandingKeySealed string `json:"branding_key_sealed"` |
| 54 | // Optional: the avatar bytes sealed under the B-derived key |
| 55 | // (base64url iv||ct). Empty keeps the current avatar state. |
| 56 | AvatarSealed string `json:"avatar_sealed"` |
| 57 | } |
| 58 | if json.NewDecoder(r.Body).Decode(&body) != nil { |
| 59 | httpError(w, http.StatusBadRequest, "bad request") |
| 60 | return |
| 61 | } |
| 62 | if body.BrandingBlob == "" || len(body.BrandingBlob) > 16*1024 || |
| 63 | body.BrandingSalt == "" || len(body.BrandingSalt) > 128 || |
| 64 | body.BrandingKeySealed == "" || len(body.BrandingKeySealed) > 1024 || |
| 65 | len(body.AvatarSealed) > 2*maxServerAvatarBytes { |
| 66 | httpError(w, http.StatusBadRequest, "bad request") |
| 67 | return |
| 68 | } |
| 69 | // The avatar first: a sealed instance must never keep serving plaintext |
| 70 | // photo bytes. If the client sends no sealed replacement (it had none, or |
| 71 | // its avatar fetch failed mid-seal), an existing PLAINTEXT photo is |
| 72 | // cleared rather than left readable behind a "sealed" flag — the admin |
| 73 | // re-seals with the photo to bring it back. An already-sealed avatar is |
| 74 | // kept (re-seals that only change text omit it). |
| 75 | if body.AvatarSealed != "" { |
| 76 | if err := s.db.setInstanceAvatar([]byte(body.AvatarSealed), sealedAvatarMime, time.Now().Unix()); err != nil { |
| 77 | httpError(w, http.StatusInternalServerError, "db error") |
| 78 | return |
| 79 | } |
| 80 | } else if _, mime, _, ok := s.db.getInstanceAvatar(); ok && mime != sealedAvatarMime { |
| 81 | if err := s.db.clearInstanceAvatar(); err != nil { |
| 82 | httpError(w, http.StatusInternalServerError, "db error") |
| 83 | return |
| 84 | } |
| 85 | } |
| 86 | // Ordered, sealed flag LAST: these writes aren't one transaction, so a |
| 87 | // mid-loop failure must never leave branding_sealed=1 beside readable |
| 88 | // plaintext — flipping the flag is the final act. |
| 89 | for _, kv := range [][2]string{ |
| 90 | {"branding_blob", body.BrandingBlob}, |
| 91 | {"branding_salt", body.BrandingSalt}, |
| 92 | {"branding_key_sealed", body.BrandingKeySealed}, |
| 93 | // Clear the plaintext the blob replaces. group_name intentionally |
| 94 | // falls back to the compiled-in default for keyless surfaces; |
| 95 | // groupNameSet() reports true while sealed (see db.go). |
| 96 | {"group_name", ""}, |
| 97 | {"group_description", ""}, |
| 98 | {"server_avatar_alt", ""}, |
| 99 | {"admin_name", ""}, |
| 100 | {"admin_email", ""}, |
| 101 | {"branding_sealed", "1"}, |
| 102 | } { |
| 103 | if err := s.db.setConfig(kv[0], kv[1]); err != nil { |
| 104 | httpError(w, http.StatusInternalServerError, "db error") |
| 105 | return |
| 106 | } |
| 107 | } |
| 108 | writeJSON(w, http.StatusOK, map[string]any{"ok": true}) |
| 109 | } |
| 110 | |
| 111 | // unsealBranding restores plaintext mode. The server cannot decrypt, so the |
| 112 | // admin's client (which just decrypted the blob) supplies the plaintext back. |
| 113 | // The sealed avatar bytes are useless in plaintext mode and are cleared; the |
| 114 | // admin re-uploads the photo via the normal setServerAvatar path. |
| 115 | func (s *Server) unsealBranding(w http.ResponseWriter, r *http.Request) { |
| 116 | if !s.requireAdmin(w, r) { |
| 117 | return |
| 118 | } |
| 119 | if !s.db.brandingSealed() { |
| 120 | httpError(w, http.StatusConflict, "branding is not sealed") |
| 121 | return |
| 122 | } |
| 123 | var body struct { |
| 124 | Name string `json:"name"` |
| 125 | Description string `json:"description"` |
| 126 | AdminName string `json:"admin_name"` |
| 127 | AdminEmail string `json:"admin_email"` |
| 128 | AvatarAlt string `json:"avatar_alt"` |
| 129 | } |
| 130 | if json.NewDecoder(r.Body).Decode(&body) != nil { |
| 131 | httpError(w, http.StatusBadRequest, "bad request") |
| 132 | return |
| 133 | } |
| 134 | if body.Name == "" || len(body.Name) > 60 { |
| 135 | httpError(w, http.StatusBadRequest, "name must be 1–60 characters") |
| 136 | return |
| 137 | } |
| 138 | // Ordered, sealed flag LAST (mirror of sealBranding): restore the |
| 139 | // plaintext, drop the blobs, and only then leave sealed mode — a mid-loop |
| 140 | // failure keeps the instance sealed and the unseal retryable. |
| 141 | for _, kv := range [][2]string{ |
| 142 | {"group_name", body.Name}, |
| 143 | {"group_description", body.Description}, |
| 144 | {"server_avatar_alt", body.AvatarAlt}, |
| 145 | {"admin_name", body.AdminName}, |
| 146 | {"admin_email", body.AdminEmail}, |
| 147 | {"branding_blob", ""}, |
| 148 | {"branding_salt", ""}, |
| 149 | {"branding_key_sealed", ""}, |
| 150 | {"branding_sealed", ""}, |
| 151 | } { |
| 152 | if err := s.db.setConfig(kv[0], kv[1]); err != nil { |
| 153 | httpError(w, http.StatusInternalServerError, "db error") |
| 154 | return |
| 155 | } |
| 156 | } |
| 157 | if _, mime, _, ok := s.db.getInstanceAvatar(); ok && mime == sealedAvatarMime { |
| 158 | if err := s.db.clearInstanceAvatar(); err != nil { |
| 159 | httpError(w, http.StatusInternalServerError, "db error") |
| 160 | return |
| 161 | } |
| 162 | } |
| 163 | writeJSON(w, http.StatusOK, map[string]any{"ok": true}) |
| 164 | } |
| 165 | |
| 166 | // requireUnsealed guards the plaintext branding setters: while sealed, a |
| 167 | // stale admin surface must not write readable branding back beside the blob. |
| 168 | // Renames and new photos go through sealBranding again (the client re-seals). |
| 169 | func (s *Server) requireUnsealed(w http.ResponseWriter) bool { |
| 170 | if s.db.brandingSealed() { |
| 171 | httpError(w, http.StatusConflict, "branding is sealed — update it via the sealed-branding flow") |
| 172 | return false |
| 173 | } |
| 174 | return true |
| 175 | } |
| 176 | |
amadan