| 1 | // Sharing a vault, and the rotation that taking somebody out of it is. |
| 2 | // |
| 3 | // A shared vault's keyset is sealed to each member's account public key by |
| 4 | // ephemeral-static ECDH — the same ECIES the device handoff uses. Two things |
| 5 | // follow from that and both are the point: |
| 6 | // |
| 7 | // - Sharing needs no unlock on the RECIPIENT's side. Sealing to a public |
| 8 | // key is free, which is what the agent surface depends on later: a daemon |
| 9 | // can be handed a vault without anybody typing a passphrase. |
| 10 | // - The server holds an envelope it has no key for, so "shared" never means |
| 11 | // "the operator can read it". |
| 12 | // |
| 13 | // The AAD is scoped to the VAULT and names the member, where the owner's own |
| 14 | // copy is scoped to the account and names the vault. Neither blob can be |
| 15 | // opened as the other, and a member's wrap cannot be moved to another member. |
| 16 | |
| 17 | import { concat, fromHex, randomBytes, toHex } from "./bytes.js"; |
| 18 | import { openFrom, sealTo, NONCE_LEN, PUBLIC_KEY_LEN } from "./ecies.js"; |
| 19 | import { sealItem } from "./items.js"; |
| 20 | import { aad, seal } from "./sealed.js"; |
| 21 | import { OBJECT_VAULT_KEYSET } from "./vaultkeys.js"; |
| 22 | |
| 23 | export class NotTheOwnerError extends Error {} |
| 24 | |
| 25 | // keysetBody is what a member receives: the vault's name and its bulk key. |
| 26 | // The drop-box private half is deliberately NOT in it — a member can read and |
| 27 | // write items without being able to open captures addressed to the vault. |
| 28 | function keysetBody(vault) { |
| 29 | return new TextEncoder().encode(JSON.stringify({ |
| 30 | name: vault.name || "", |
| 31 | k_vault: toHex(vault.kVault), |
| 32 | })); |
| 33 | } |
| 34 | |
| 35 | // splitEnvelope turns an ECIES envelope into the three fields the API stores |
| 36 | // separately, so the wire shape matches every other sealed row rather than |
| 37 | // inventing a fourth encoding for this one case. |
| 38 | function splitEnvelope(envelope) { |
| 39 | return { |
| 40 | ephemeral_public_key_hex: toHex(envelope.slice(0, PUBLIC_KEY_LEN)), |
| 41 | sealed: { |
| 42 | nonce_hex: toHex(envelope.slice(PUBLIC_KEY_LEN, PUBLIC_KEY_LEN + NONCE_LEN)), |
| 43 | ciphertext_hex: toHex(envelope.slice(PUBLIC_KEY_LEN + NONCE_LEN)), |
| 44 | }, |
| 45 | }; |
| 46 | } |
| 47 | |
| 48 | // lookupAccount resolves the public key to seal to. By account id, never by |
| 49 | // address: an address-to-account endpoint would be an existence oracle for |
| 50 | // every address anybody cared to try. |
| 51 | export async function lookupAccount(net, accountIdHex) { |
| 52 | return net.get(`/api/account-key?account=${encodeURIComponent(accountIdHex)}`); |
| 53 | } |
| 54 | |
| 55 | export async function members(net, vault) { |
| 56 | const { members: rows } = await net.get(`/api/members?vault=${vault.idHex}`); |
| 57 | return rows; |
| 58 | } |
| 59 | |
| 60 | // share seals this vault's keyset to one account and posts it. |
| 61 | export async function share(net, vault, memberIdHex, memberPublicKeyHex) { |
| 62 | if (!vault.owned) { |
| 63 | throw new NotTheOwnerError( |
| 64 | "contra: only the owner of a vault can share it"); |
| 65 | } |
| 66 | const memberId = fromHex(memberIdHex); |
| 67 | const envelope = await sealTo( |
| 68 | fromHex(memberPublicKeyHex), |
| 69 | aad(vault.id, OBJECT_VAULT_KEYSET, memberId, 1), |
| 70 | keysetBody(vault)); |
| 71 | |
| 72 | await net.post("/api/members", { |
| 73 | vault_id_hex: vault.idHex, |
| 74 | account_id_hex: memberIdHex, |
| 75 | ...splitEnvelope(envelope), |
| 76 | }); |
| 77 | } |
| 78 | |
| 79 | // openSharedKeyset is the receiving half, used by unlock. Exported so a test |
| 80 | // can exercise it directly against a wrap the API returned. |
| 81 | export async function openSharedKeyset(dAcct, acctPublic, accountId, vaultId, row) { |
| 82 | const envelope = concat( |
| 83 | fromHex(row.ephemeral_public_key_hex), |
| 84 | fromHex(row.keyset.nonce_hex), |
| 85 | fromHex(row.keyset.ciphertext_hex)); |
| 86 | return JSON.parse(new TextDecoder().decode(await openFrom( |
| 87 | dAcct, acctPublic, aad(vaultId, OBJECT_VAULT_KEYSET, accountId, 1), envelope))); |
| 88 | } |
| 89 | |
| 90 | // rotate is revocation, and it is also how a vault heals after any exposure. |
| 91 | // |
| 92 | // It composes the whole new state in the browser and posts it as one body: |
| 93 | // a new keyset sealed under RK for the owner, every item re-sealed under the |
| 94 | // new key, and a wrap of the new keyset for each member who remains. Whoever |
| 95 | // is not in `keep` stops being a member — which is why removal has no call of |
| 96 | // its own. In a seal-to-public-key model revocation IS rotation, because the |
| 97 | // removed member may already hold K_vault. |
| 98 | // |
| 99 | // What this does NOT do, and no honest implementation can: un-download what |
| 100 | // somebody already has. PROTOCOL.md says so and the copy must not soften it. |
| 101 | export async function rotate(net, opened, vault, items, keep, newKVault) { |
| 102 | if (!vault.owned) { |
| 103 | throw new NotTheOwnerError( |
| 104 | "contra: only the owner of a vault can rotate it"); |
| 105 | } |
| 106 | const rotated = { ...vault, kVault: newKVault }; |
| 107 | |
| 108 | // The owner's own copy, under RK, with the AAD it has always had. |
| 109 | const nonce = randomBytes(12); |
| 110 | const keyset = { |
| 111 | nonce_hex: toHex(nonce), |
| 112 | ciphertext_hex: toHex(await seal( |
| 113 | opened.rk, nonce, |
| 114 | aad(opened.accountId, OBJECT_VAULT_KEYSET, vault.id, 1), |
| 115 | keysetBody(rotated))), |
| 116 | }; |
| 117 | |
| 118 | // Every item, re-sealed under the new key with its version bumped. Eager |
| 119 | // rather than lazy: lazy rotation needs a per-item key-generation marker, |
| 120 | // and that marker tells the operator which items changed since a removal. |
| 121 | const reSealed = []; |
| 122 | for (const item of items) { |
| 123 | const version = item.version + 1; |
| 124 | reSealed.push({ |
| 125 | item_id_hex: item.idHex, |
| 126 | version, |
| 127 | ...await sealItem(vault.id, newKVault, item.id, version, item.fields), |
| 128 | }); |
| 129 | } |
| 130 | |
| 131 | const wraps = []; |
| 132 | for (const m of keep) { |
| 133 | const envelope = await sealTo( |
| 134 | fromHex(m.public_key_hex), |
| 135 | aad(vault.id, OBJECT_VAULT_KEYSET, fromHex(m.account_id_hex), 1), |
| 136 | keysetBody(rotated)); |
| 137 | const { ephemeral_public_key_hex: eph, sealed } = splitEnvelope(envelope); |
| 138 | wraps.push({ |
| 139 | account_id_hex: m.account_id_hex, |
| 140 | ephemeral_public_key_hex: eph, |
| 141 | ...sealed, |
| 142 | }); |
| 143 | } |
| 144 | |
| 145 | const res = await net.post("/api/vault/rotate", { |
| 146 | vault_id_hex: vault.idHex, |
| 147 | expected_epoch: vault.epoch, |
| 148 | keyset, |
| 149 | items: reSealed, |
| 150 | members: wraps, |
| 151 | }); |
| 152 | return { ...rotated, epoch: res.epoch }; |
| 153 | } |
| 154 | |
amadan