Create, import and store a wallet (Android engine)
`Wallet` makes one, adopts one from a phrase somebody typed, and reads the phrase back; the vault seals the record at rest. 🔴 The property guarded hardest is a NEGATIVE one: a wallet must not be derivable from the account. The entropy is fresh randomness — never the passphrase, the handle, or the Flamenet identity. Deriving it from the passphrase would be convenient, would need no backup at all, and would tie every payment somebody ever received to their handle on a public ledger for ever. The chain does not forget, so there is no undoing it later. A test asserts that eight wallets made in a row share nothing, which is what would catch that shortcut being taken. 🔴 The record stores the ENTROPY, never the seed. The seed is a one-way function of the phrase, so a record holding it would open the wallet and be unable to produce the words: somebody who lost their phrase but still had their account could spend, and could never write it down again or move to another wallet. Self-custody in name only. ⚠️ Erasing the device destroys the record, and the phrase is then the only copy that exists. Checked rather than assumed while writing this: plain sign-out keeps the vault and `updatePassword` uses the plain door, so a password change does NOT cost somebody their wallet; `signOut(erasingDevice = true)` and `deleteAccount` destroy it. That is what a recovery phrase is for, and it has to be said at the moment the phrase is shown rather than discovered afterwards. ⚠️ An imported phrase is validated BEFORE it is stored. One that fails its checksum is refused at import rather than saved and discovered later, when the wallet it names turns out to be empty and nobody can say why. ⚠️ The receive counter is carried across a rewrite rather than reset. Resuming at zero would hand out addresses somebody has already been paid at, undoing the one linkability a wallet can prevent. ⚠️ `SecureRandom()` with no seeding call. Seeding it from a timestamp or a device id would make the wallet reconstructible from things that are not secret — the same failure as deriving it from the passphrase, wearing a different hat. 9 tests. App builds, every JVM suite green. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Paul Hitt
co-authored by
Claude Opus 5
Claude Opus 5
parent
2e8c6776e2
commit
227c098da7
@@ -1667,6 +1667,59 @@ class Vault(private val storage: Storage, private val key: SecretKey) {
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storage.delete(pinnedName(threadId))
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}
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// -- Wallet -------------------------------------------------------------
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private val walletName = "wallet-record"
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/**
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* The wallet's ENTROPY, sealed at rest, or null if there is no wallet.
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*
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* 🔴 **The entropy, never the seed.** The seed is a one-way function of the
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* phrase, so a record holding it would open the wallet and be unable to
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* produce the words — somebody who lost their phrase but still had their
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* account could spend, and could never write the phrase down again or move
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* to another wallet. Self-custody in name only. Keeping the entropy means
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* the phrase can always be regenerated from the record.
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*
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* ⚠️ **Sealed by the vault, which means erasing this device destroys it.**
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* Plain sign-out keeps it (and so does a password change, which signs out
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* plainly); "erase this phone" and "delete account" do not. After those, the
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* recovery phrase is the only copy that exists — which is the whole point of
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* a recovery phrase, and has to be SAID rather than discovered.
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*/
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fun walletEntropy(): ByteArray? =
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readJson(walletName)?.optString("entropy")?.takeIf { it.isNotEmpty() }
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?.let { runCatching { Bytes.unb64(it) }.getOrNull() }
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fun saveWalletEntropy(entropy: ByteArray) {
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val existing = readJson(walletName)
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writeJson(walletName, JSONObject()
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.put("entropy", Bytes.b64(entropy))
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// ⚠️ The counter is carried across a rewrite rather than reset. A
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// restore that zeroed it would hand out addresses somebody has
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// already been paid at, undoing the one linkability the wallet can
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// prevent.
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.put("next", existing?.optInt("next", 0) ?: 0))
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}
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/** How many receive addresses have been handed out. */
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fun walletNextIndex(): Int = readJson(walletName)?.optInt("next", 0) ?: 0
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/**
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* Advance the receive counter.
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*
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* ⚠️ Never goes backwards, for the reason above: an index that repeated
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* would show an address that has already been used.
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*/
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fun saveWalletNextIndex(next: Int) {
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val record = readJson(walletName) ?: return
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if (next <= record.optInt("next", 0)) return
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writeJson(walletName, record.put("next", next))
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}
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/** Forget the wallet entirely. The phrase is then the only copy. */
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fun forgetWallet() = storage.delete(walletName)
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// -- Home-record rollback floor (§20.4) ----------------------------------
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private fun homeSerialName(fnid: String) = "home-serial-${Bytes.b64(Bytes.sha256(fnid.toByteArray(Charsets.UTF_8))).take(22).replace('/', '_')}"
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@@ -0,0 +1,75 @@
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package io.flamenet.e2e
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import java.security.SecureRandom
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/**
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* Creating, importing and reading back a wallet.
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*
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* 🔴 **Addresses are independent of who you are, by construction.** The entropy
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* is fresh randomness — never derived from the passphrase, the handle, or the
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* Flamenet identity — so no address can be computed from an account and no
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* account from an address. Deriving a wallet from the account passphrase would
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* be *convenient*, would need no backup at all, and would tie every payment
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* somebody ever received to their handle on a public ledger for ever. It is the
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* one shortcut this file exists to refuse.
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*
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* ⚠️ **The phrase is the only copy that survives erasing the device.** The
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* record is sealed by the vault, so plain sign-out keeps it and a password
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* change keeps it — but "erase this phone" and "delete account" destroy it.
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* That is what a recovery phrase is for, and it has to be said out loud at the
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* moment the phrase is shown, not discovered afterwards.
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*/
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object Wallet {
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/**
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* A new wallet: the phrase to write down, and the entropy to store.
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*
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* ⚠️ 256 bits by default — 24 words. The extra length costs nothing to
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* store and is what people expect from a wallet; 128 bits stays available
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* for anybody who wants 12.
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*
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* 🔴 `SecureRandom()` with no seeding call. Seeding it from anything —
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* a timestamp, a device id, the account — would make the wallet
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* reconstructible from things that are not secret, which is the same
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* failure as deriving it from the passphrase.
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*/
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fun create(words: List<String>, entropyBytes: Int = 32, random: SecureRandom = SecureRandom()):
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Created {
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val entropy = ByteArray(entropyBytes).also(random::nextBytes)
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return Created(phrase = Bip39.phrase(entropy, words), entropy = entropy)
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}
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data class Created(val phrase: String, val entropy: ByteArray) {
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override fun equals(other: Any?) = other is Created &&
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phrase == other.phrase && entropy.contentEquals(other.entropy)
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override fun hashCode() = 31 * phrase.hashCode() + entropy.contentHashCode()
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}
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/**
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* Adopt a phrase that came from somewhere else.
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*
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* ⚠️ **Validated before it is stored.** A phrase that fails its checksum is
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* refused here rather than saved and discovered later, when the wallet it
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* names turns out to be empty and nobody can say why.
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*/
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fun import(phrase: String, words: List<String>): ByteArray =
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Bip39.entropy(phrase, words)
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/** The phrase again, from stored entropy — for showing it a second time. */
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fun phrase(entropy: ByteArray, words: List<String>): String =
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Bip39.phrase(entropy, words)
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/**
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* The 64-byte seed everything derives from.
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*
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* ⚠️ [passphrase] is BIP-39's, not the account's. A different one silently
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* yields a DIFFERENT valid wallet — the standard's design, and a sharp edge
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* worth naming wherever it is offered to somebody.
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*/
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fun seed(entropy: ByteArray, words: List<String>, passphrase: String = ""): ByteArray =
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Bip39.seed(phrase(entropy, words), passphrase)
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/** The account this wallet's addresses come from. */
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fun account(entropy: ByteArray, words: List<String>, nextIndex: Long = 0): HdAccount =
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HdAccount(seed(entropy, words), nextIndex = nextIndex)
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}
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@@ -0,0 +1,147 @@
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package io.flamenet.e2e
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import java.security.SecureRandom
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import kotlin.test.Test
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import kotlin.test.assertContentEquals
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import kotlin.test.assertEquals
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import kotlin.test.assertFailsWith
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import kotlin.test.assertNotEquals
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import kotlin.test.assertTrue
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/**
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* Creating, importing and reading back a wallet.
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*
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* 🔴 **The property worth guarding hardest is a negative one: the wallet must
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* NOT be derivable from the account.** Deriving it from the passphrase would be
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* convenient, would need no backup at all, and would tie every payment somebody
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* ever received to their handle on a public ledger for ever. There is no way to
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* undo that later — the chain does not forget — so it is asserted rather than
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* left to good intentions.
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*/
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class WalletTest {
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private val words by lazy { Bip39.englishWordlist() }
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/** Deterministic randomness, so a create() can be asserted against. */
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private fun fixedRandom(fill: Byte) = object : SecureRandom() {
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override fun nextBytes(bytes: ByteArray) { bytes.fill(fill) }
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}
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// ---- What a wallet is not --------------------------------------------
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/**
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* 🔴 Two wallets made in a row share nothing. If `create` ever started
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* deriving from something about the account, this is what would catch it.
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*/
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@Test
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fun `every wallet created is a different one`() {
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val phrases = (1..8).map { Wallet.create(words).phrase }
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assertEquals(8, phrases.toSet().size, "create() is not producing fresh entropy")
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}
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@Test
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fun `a created wallet is 24 words by default and can be 12`() {
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assertEquals(24, Wallet.create(words).phrase.split(" ").size)
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assertEquals(12, Wallet.create(words, entropyBytes = 16).phrase.split(" ").size)
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}
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/** The entropy really is what the phrase encodes, not a parallel value. */
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@Test
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fun `the phrase and the stored entropy are the same secret`() {
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val made = Wallet.create(words, random = fixedRandom(0x2a))
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assertContentEquals(made.entropy, Bip39.entropy(made.phrase, words))
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assertEquals(made.phrase, Wallet.phrase(made.entropy, words))
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}
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// ---- Importing -------------------------------------------------------
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/**
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* ⚠️ Validated before it is stored. A phrase that fails its checksum is
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* refused here rather than saved and discovered later, when the wallet it
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* names turns out to be empty and nobody can say why.
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*/
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@Test
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fun `a phrase that does not check out is refused at import`() {
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val real = Wallet.create(words).phrase
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val broken = real.split(" ").toMutableList().also { it[0] = it[1] }.joinToString(" ")
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assertFailsWith<Bip39.Failure.ChecksumFailed> { Wallet.import(broken, words) }
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}
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@Test
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fun `a phrase containing a word that is not on the list is refused`() {
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val real = Wallet.create(words).phrase.split(" ").toMutableList()
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real[3] = "flamenet"
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assertFailsWith<Bip39.Failure.UnknownWord> {
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Wallet.import(real.joinToString(" "), words)
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}
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}
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/** 🔴 An imported phrase gives back exactly the wallet it names. */
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@Test
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fun `importing a phrase restores the same addresses`() {
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val made = Wallet.create(words)
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val imported = Wallet.import(made.phrase, words)
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assertContentEquals(made.entropy, imported)
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assertEquals(
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Wallet.account(made.entropy, words).receive(0).address,
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Wallet.account(imported, words).receive(0).address,
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)
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}
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// ---- The counter -----------------------------------------------------
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/**
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* ⚠️ A restored wallet resumes at the index it was left at, when one is
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* known. Resuming at zero would hand out addresses somebody has already
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* been paid at, undoing the one linkability the wallet can prevent.
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*/
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@Test
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fun `an account can resume from a stored index`() {
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val made = Wallet.create(words)
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val resumed = Wallet.account(made.entropy, words, nextIndex = 5)
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assertEquals(5L, resumed.nextIndex)
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val (receive, _) = resumed.next()
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assertEquals(
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Wallet.account(made.entropy, words).receive(5).address,
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receive.address,
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)
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}
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// ---- The BIP-39 passphrase -------------------------------------------
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/**
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* 🔴 A BIP-39 passphrase silently names a DIFFERENT wallet. That is the
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* standard's design and the sharpest edge in it: somebody who mistypes one
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* does not get an error, they get an empty account.
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*/
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@Test
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fun `a BIP-39 passphrase produces a different wallet from the same phrase`() {
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val made = Wallet.create(words)
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val plain = HdAccount(Wallet.seed(made.entropy, words)).receive(0).address
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val guarded = HdAccount(Wallet.seed(made.entropy, words, "extra")).receive(0).address
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assertNotEquals(plain, guarded)
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}
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// ---- End to end ------------------------------------------------------
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/**
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* The whole promise, in one test: write these words down, and any
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* implementation anywhere gives back these addresses.
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*/
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@Test
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fun `a phrase written down restores the same wallet`() {
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val made = Wallet.create(words, random = fixedRandom(0x11))
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val addresses = (0L..3L).map {
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Wallet.account(made.entropy, words).receive(it).address
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}
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// Somebody types the words into a fresh install.
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val restored = Wallet.import(made.phrase, words)
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val restoredAddresses = (0L..3L).map {
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Wallet.account(restored, words).receive(it).address
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}
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assertEquals(addresses, restoredAddresses)
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assertTrue(addresses.all { HdAccount.looksLikeAddress(it) })
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}
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}
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