Merge branch 'main' into chore/perf-privacy-polish

Baseline .swiftlint.yml for local use (not wired into CI yet):

- file_length: warning at 600, error at 4000 — above the current
  maximum (BLEService.swift, ~3,500 lines), so the codebase passes
  as-is and only future growth trips the error.
- function_body_length: warning 100, error 200.
- Disables the high-noise style rules (line_length, identifier_name,
  cyclomatic_complexity, force_cast/force_try for tests, etc.) so the
  remaining defaults stay actionable; SwiftLint is not installed in
  this environment, so the disabled list is a best-effort starting
  point to be tuned on first real run.
- Excludes vendored Arti and SwiftPM .build output.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -6,7 +6,6 @@
 plans/
 
 ## AI
-CLAUDE.md
 AGENTS.md
 .claude/
 

.swiftlint.yml

@@ -0,0 +1,51 @@
+# SwiftLint configuration for BitChat.
+#
+# Intentionally pragmatic: rules that would flood the existing codebase are
+# disabled so the lint signal stays actionable; re-enable them individually as
+# files get cleaned up. Not wired into CI yet — run locally with `swiftlint`
+# from the repo root.
+
+included:
+  - bitchat
+  - bitchatTests
+  - localPackages/BitFoundation/Sources
+  - localPackages/BitFoundation/Tests
+  - localPackages/BitLogger/Sources
+
+excluded:
+  - .build
+  - localPackages/Arti
+  - localPackages/BitFoundation/.build
+  - localPackages/BitLogger/.build
+
+disabled_rules:
+  # Style/volume rules that currently produce noise across the codebase.
+  - line_length
+  - identifier_name
+  - type_name
+  - type_body_length
+  - cyclomatic_complexity
+  - function_parameter_count
+  - large_tuple
+  - nesting
+  - todo
+  - trailing_comma
+  - opening_brace
+  - statement_position
+  - for_where
+  - redundant_string_enum_value
+  - non_optional_string_data_conversion
+  # Common in tests (force casts/tries on fixtures).
+  - force_cast
+  - force_try
+
+file_length:
+  warning: 600
+  # BLEService.swift is currently ~3,500 lines; the error threshold sits above
+  # today's maximum so the codebase passes as-is and only future growth of the
+  # largest files trips it.
+  error: 4000
+
+function_body_length:
+  warning: 100
+  error: 200

CLAUDE.md

@@ -0,0 +1,106 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build & Test Commands
+
+```bash
+# Build macOS (no signing)
+xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" -configuration Debug CODE_SIGNING_ALLOWED=NO build
+
+# Build iOS for simulator
+xcodebuild -project bitchat.xcodeproj -scheme "bitchat (iOS)" -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 15' build
+
+# Run all tests (iOS simulator)
+xcodebuild -project bitchat.xcodeproj -scheme bitchat -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 15' test
+
+# Run tests via Swift Package Manager (used in CI)
+swift build && swift test --parallel
+
+# Clean build
+xcodebuild -project bitchat.xcodeproj -scheme "bitchat (macOS)" clean
+
+# Quick dev build and run (macOS only, requires `just`)
+just run
+```
+
+### Running Specific Tests
+
+```bash
+# Run a single test class
+xcodebuild test -project bitchat.xcodeproj -scheme bitchat -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 15' -only-testing:bitchatTests/IntegrationTests
+
+# Run a single test method
+xcodebuild test -project bitchat.xcodeproj -scheme bitchat -sdk iphonesimulator -destination 'platform=iOS Simulator,name=iPhone 15' -only-testing:bitchatTests/NoiseProtocolTests/testHandshake
+```
+
+## Architecture Overview
+
+BitChat is a **dual-transport P2P messaging app**: Bluetooth mesh for offline local communication, Nostr protocol for internet-based global messaging.
+
+### Local Packages (`localPackages/`)
+
+- **BitFoundation**: Shared foundation types — `BinaryProtocol` (compact binary packet format for BLE), `BitchatPacket`, `BitchatMessage`, `PeerID`, hex/SHA256/compression utilities. Has its own test suite under `localPackages/BitFoundation/Tests` (run `swift test` inside the package).
+- **BitLogger**: `SecureLogger` logging.
+- **Arti**: Tor integration (exposes the `Tor` product).
+
+### Transport Layer
+
+- **BLEService** (`bitchat/Services/BLE/BLEService.swift`): Core Bluetooth LE mesh networking - peer discovery, connection management, multi-hop relay (max 7 hops), packet fragmentation. The BLE directory contains ~40 focused collaborators (handlers, policies, buffers): `BLEReceivePipeline` dispatches inbound packets to `BLEAnnounceHandler` / `BLENoisePacketHandler` / `BLEPublicMessageHandler` / `BLEFragmentHandler` etc.; outbound planning lives in the `BLEOutbound*` types; peer state in `BLEPeerRegistry`.
+- **NostrTransport** (`bitchat/Services/NostrTransport.swift`): Internet transport via Nostr relays with NIP-17 encryption
+- **Transport protocol** (`bitchat/Services/Transport.swift`): Common interface both transports implement
+
+### Encryption Layer
+
+- **NoiseProtocol** (`bitchat/Noise/`): Noise XX pattern for end-to-end encryption with forward secrecy
+  - `NoiseEncryptionService`: Main encryption/decryption API
+  - `NoiseSessionManager`: Thread-safe per-peer session management
+  - `NoiseSession`: Individual peer session state (handshake, send/receive ciphers)
+- **NostrProtocol** (`bitchat/Nostr/NostrProtocol.swift`): NIP-17 gift-wrapped encryption for Nostr messages
+
+### Protocol Layer
+
+- **BinaryProtocol** (`localPackages/BitFoundation/Sources/BitFoundation/BinaryProtocol.swift`): Compact binary packet format for BLE (lives in BitFoundation, not `bitchat/Protocols/`)
+- **BitchatProtocol** (`bitchat/Protocols/BitchatProtocol.swift`): Message types and packet structures
+- **LocationChannel/Geohash** (`bitchat/Protocols/`): Geographic channel routing
+
+### Application Layer
+
+- **AppRuntime** (`bitchat/App/AppRuntime.swift`): Composition root. Owns `ChatViewModel`, `ConversationStore`, the feature models (`PublicChatModel`, `PeerListModel`, `LocationPresenceStore`, `PeerIdentityStore`, ...), and the app event stream.
+- **ConversationStore** (`bitchat/App/ConversationStore.swift`): Single-writer, single source of truth for conversation message state and selection (see `docs/CONVERSATION-STORE-DESIGN.md`). Feature models and `ChatViewModel` observe it and mutate it through its intent API.
+- **ChatViewModel** (`bitchat/ViewModels/ChatViewModel.swift`, ~1,600 lines): Central coordinator that wires and delegates to ~25 focused coordinator/pipeline types in `bitchat/ViewModels/`, e.g.:
+  - `ChatPrivateConversationCoordinator` / `ChatPublicConversationCoordinator`: DM and public chat flows
+  - `ChatNostrCoordinator` → `GeohashSubscriptionManager`, `NostrInboundPipeline`, `GeoPresenceTracker`, `GeoChannelCoordinator`: Nostr/geohash channel logic
+  - `ChatOutgoingCoordinator`, `ChatDeliveryCoordinator`, `PublicMessagePipeline`: send paths and delivery tracking
+  - `ChatMediaTransferCoordinator`, `ChatMediaPreparation`: media transfers
+  - `ChatLifecycleCoordinator`, `ChatTransportEventCoordinator`, `ChatPeerListCoordinator`, `ChatPeerIdentityCoordinator`, `ChatVerificationCoordinator`: lifecycle, transport events, peer state
+  - `bitchat/ViewModels/Extensions/` (`ChatViewModel+Nostr/+PrivateChat/+Tor`): thin delegation shims kept for call-site stability; the real logic lives in the coordinators
+- **MessageRouter** (`bitchat/Services/MessageRouter.swift`): Intelligent transport selection (BLE → Nostr fallback)
+- **PrivateChatManager** (`bitchat/Services/PrivateChatManager.swift`): DM session management
+
+## Test Infrastructure
+
+Tests use an **in-memory networking harness** for deterministic, race-free testing:
+
+- **MockBLEService** (`bitchatTests/Mocks/MockBLEService.swift`): Simulated BLE mesh with configurable topology
+  - `MockBLEService.resetTestBus()` - Clear state in setUp()
+  - `simulateConnectedPeer(_:)` / `simulateDisconnectedPeer(_:)` - Configure topology
+  - `autoFloodEnabled` - Enable broadcast flooding for Integration tests only
+
+- **Test categories**:
+  - `bitchatTests/EndToEnd/`: Full message flow tests with explicit routing
+  - `bitchatTests/Integration/`: Multi-node topology tests with auto-flooding
+  - Unit tests: Individual component tests
+
+## Key Patterns
+
+- **Threading**: Use `@MainActor` for UI, `Task { @MainActor in ... }` for main thread dispatch
+- **Delegation**: `BitchatDelegate`, `TransportPeerEventsDelegate` for event propagation
+- **Session recovery**: On decrypt failure, clear local session and re-initiate Noise handshake (no NACK)
+
+## Device Setup
+
+To run on physical devices:
+1. Copy `Configs/Local.xcconfig.example` to `Configs/Local.xcconfig`
+2. Add your Developer Team ID to `Local.xcconfig`
+3. Replace `group.chat.bitchat` with `group.<your_bundle_id>` in entitlements

bitchat/Nostr/NostrProtocol.swift

@@ -328,52 +328,85 @@ struct NostrProtocol {
         return try NostrEvent(from: rumorDict)
     }
     
-    // MARK: - Encryption (NIP-44 v2)
-    
-    private static func encrypt(
+    // MARK: - Encryption (NIP-44 v2/v3)
+
+    /// Whether outgoing DMs use the padded "v3:" envelope.
+    ///
+    /// TWO-PHASE ROLLOUT — DO NOT FLIP YET. Deployed clients hard-reject any
+    /// ciphertext that does not start with "v2:" (`decrypt` below, as shipped,
+    /// throws `invalidCiphertext` on unknown version prefixes), and the "v2:"
+    /// payload is the raw UTF-8 rumor JSON, so a padded payload cannot be
+    /// smuggled inside "v2:" without breaking old receivers either. Enabling
+    /// this today would strand every client in the field.
+    ///
+    /// Phase 1 (this change): ship decrypt-side support for "v3:" everywhere.
+    /// Phase 2 (future release, once phase-1 clients are widely deployed):
+    /// set this to true so outgoing DMs stop leaking plaintext length to
+    /// relays.
+    static let sendPaddedEnvelope = false
+
+    /// Internal (rather than private) so tests can exercise both envelope
+    /// versions directly.
+    static func encrypt(
         plaintext: String,
         recipientPubkey: String,
-        senderKey: P256K.Schnorr.PrivateKey
+        senderKey: P256K.Schnorr.PrivateKey,
+        padded: Bool = NostrProtocol.sendPaddedEnvelope
     ) throws -> String {
-        
+
         guard let recipientPubkeyData = Data(hexString: recipientPubkey) else {
             throw NostrError.invalidPublicKey
         }
-        
-        // Encrypting message (NIP-44 v2: XChaCha20-Poly1305, versioned)
-        
+
+        // Encrypting message (XChaCha20-Poly1305, versioned envelope)
+
         // Derive shared secret
         let sharedSecret = try deriveSharedSecret(
             privateKey: senderKey,
             publicKey: recipientPubkeyData
         )
-        // Derive NIP-44 v2 symmetric key (HKDF-SHA256 with label in info)
+        // Derive NIP-44 v2 symmetric key (HKDF-SHA256 with label in info).
+        // The v3 envelope deliberately reuses the same key derivation; it only
+        // changes the payload framing (length prefix + padding).
         let key = try deriveNIP44V2Key(from: sharedSecret)
-        
+
         // 24-byte random nonce for XChaCha20-Poly1305
         var nonce24 = Data(count: 24)
         _ = nonce24.withUnsafeMutableBytes { ptr in
             SecRandomCopyBytes(kSecRandomDefault, 24, ptr.baseAddress!)
         }
-        
+
+        // v2 payload: raw UTF-8 plaintext (length leaks to relays)
+        // v3 payload: NIP-44 style [2-byte BE length][plaintext][zero padding]
         let pt = Data(plaintext.utf8)
-        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: pt, key: key, nonce24: nonce24)
-        
-        // v2: base64url(nonce24 || ciphertext || tag)
+        let payload = padded ? try NIP44Padding.pad(pt) : pt
+        let sealed = try XChaCha20Poly1305Compat.seal(plaintext: payload, key: key, nonce24: nonce24)
+
+        // version prefix + base64url(nonce24 || ciphertext || tag)
         var combined = Data()
         combined.append(nonce24)
         combined.append(sealed.ciphertext)
         combined.append(sealed.tag)
-        return "v2:" + Base64URLCoding.encode(combined)
+        return (padded ? "v3:" : "v2:") + Base64URLCoding.encode(combined)
     }
-    
-    private static func decrypt(
+
+    /// Internal (rather than private) so tests can exercise both envelope
+    /// versions directly.
+    static func decrypt(
         ciphertext: String,
         senderPubkey: String,
         recipientKey: P256K.Schnorr.PrivateKey
     ) throws -> String {
-        // Expect NIP-44 v2 format
-        guard ciphertext.hasPrefix("v2:") else { throw NostrError.invalidCiphertext }
+        // Accept both the legacy unpadded "v2:" envelope and the padded "v3:"
+        // envelope (see `sendPaddedEnvelope` for the rollout plan).
+        let isPadded: Bool
+        if ciphertext.hasPrefix("v2:") {
+            isPadded = false
+        } else if ciphertext.hasPrefix("v3:") {
+            isPadded = true
+        } else {
+            throw NostrError.invalidCiphertext
+        }
         let encoded = String(ciphertext.dropFirst(3))
         guard let data = Base64URLCoding.decode(encoded),
               data.count > (24 + 16),
@@ -399,18 +432,23 @@ struct NostrProtocol {
         }
 
         // If 32 bytes (x-only) try both parities, otherwise single try
+        let payload: Data
         if senderPubkeyData.count == 32 {
             let even = Data([0x02]) + senderPubkeyData
             if let pt = try? attemptDecrypt(using: even) {
-                return String(data: pt, encoding: .utf8) ?? ""
+                payload = pt
+            } else {
+                let odd = Data([0x03]) + senderPubkeyData
+                payload = try attemptDecrypt(using: odd)
             }
-            let odd = Data([0x03]) + senderPubkeyData
-            let pt = try attemptDecrypt(using: odd)
-            return String(data: pt, encoding: .utf8) ?? ""
         } else {
-            let pt = try attemptDecrypt(using: senderPubkeyData)
-            return String(data: pt, encoding: .utf8) ?? ""
+            payload = try attemptDecrypt(using: senderPubkeyData)
         }
+
+        // The AEAD tag has already authenticated the payload; unpadding
+        // failures here mean a malformed sender, not a wrong key.
+        let plaintextData = isPadded ? try NIP44Padding.unpad(payload) : payload
+        return String(data: plaintextData, encoding: .utf8) ?? ""
     }
     
     private static func deriveSharedSecret(
@@ -641,6 +679,60 @@ enum NostrError: Error {
     case encryptionFailed
 }
 
+// MARK: - NIP-44 style padding (v3 envelope payload framing)
+
+/// Payload framing for the padded "v3:" envelope, modeled on NIP-44 v2:
+/// `[2-byte big-endian plaintext length][plaintext][zero padding]`, where the
+/// total is padded to `paddedLength(for:)` — power-of-two-derived buckets with
+/// a 32-byte minimum — so ciphertext length no longer reveals exact plaintext
+/// length to relays.
+enum NIP44Padding {
+    static let minPaddedLength = 32
+    static let maxPlaintextLength = 65535
+
+    /// NIP-44's calc_padded_len: pad to 32 bytes minimum, then to a chunk
+    /// granularity of max(32, nextPowerOfTwo/8).
+    static func paddedLength(for unpaddedLength: Int) -> Int {
+        guard unpaddedLength > minPaddedLength else { return minPaddedLength }
+        // Smallest power of two strictly greater than (unpaddedLength - 1).
+        let nextPower = 1 << (Int.bitWidth - (unpaddedLength - 1).leadingZeroBitCount)
+        let chunk = nextPower <= 256 ? 32 : nextPower / 8
+        return chunk * ((unpaddedLength - 1) / chunk + 1)
+    }
+
+    /// Prefix plaintext with its 2-byte big-endian length and zero-pad to the
+    /// bucketed length. Rejects empty plaintexts and plaintexts that do not
+    /// fit the 16-bit length prefix.
+    static func pad(_ plaintext: Data) throws -> Data {
+        let length = plaintext.count
+        guard length >= 1, length <= maxPlaintextLength else {
+            throw NostrError.encryptionFailed
+        }
+        let padded = paddedLength(for: length)
+        var result = Data(capacity: 2 + padded)
+        result.append(UInt8(length >> 8))
+        result.append(UInt8(length & 0xFF))
+        result.append(plaintext)
+        result.append(Data(count: padded - length))
+        return result
+    }
+
+    /// Read the 2-byte length prefix, validate the total padded size matches
+    /// it exactly, and return the plaintext. Throws on any inconsistency so a
+    /// malformed (already-authenticated) payload can never over- or
+    /// under-read.
+    static func unpad(_ padded: Data) throws -> Data {
+        guard padded.count >= 2 else { throw NostrError.invalidCiphertext }
+        let start = padded.startIndex
+        let length = Int(padded[start]) << 8 | Int(padded[start + 1])
+        guard length >= 1,
+              padded.count == 2 + paddedLength(for: length) else {
+            throw NostrError.invalidCiphertext
+        }
+        return padded.subdata(in: (start + 2)..<(start + 2 + length))
+    }
+}
+
 // MARK: - NIP-44 v2 helpers (XChaCha20-Poly1305)
 
 private extension NostrProtocol {

bitchatTests/NostrProtocolTests.swift

@@ -289,6 +289,159 @@ struct NostrProtocolTests {
         #expect(object["limit"] as? Int == 42)
     }
 
+    // MARK: - Padding (v3 envelope)
+
+    @Test func paddedLengthMatchesNIP44Buckets() {
+        // Vectors from the NIP-44 reference test suite (calc_padded_len).
+        let vectors: [(Int, Int)] = [
+            (1, 32), (16, 32), (32, 32), (33, 64), (37, 64), (45, 64), (49, 64),
+            (64, 64), (65, 96), (100, 128), (111, 128), (200, 224), (250, 256),
+            (320, 320), (383, 384), (384, 384), (400, 448), (500, 512),
+            (512, 512), (515, 640), (700, 768), (800, 896), (900, 1024),
+            (1020, 1024), (65535, 65536)
+        ]
+        for (unpadded, expected) in vectors {
+            #expect(
+                NIP44Padding.paddedLength(for: unpadded) == expected,
+                "paddedLength(for: \(unpadded)) should be \(expected)"
+            )
+        }
+    }
+
+    @Test func padUnpadRoundTrip() throws {
+        for length in [1, 2, 31, 32, 33, 100, 320, 1020, 4096, 65535] {
+            let plaintext = Data((0..<length).map { _ in UInt8.random(in: .min ... .max) })
+            let padded = try NIP44Padding.pad(plaintext)
+            #expect(padded.count == 2 + NIP44Padding.paddedLength(for: length))
+            let unpadded = try NIP44Padding.unpad(padded)
+            #expect(unpadded == plaintext)
+        }
+    }
+
+    @Test func padHidesExactLengthWithinBucket() throws {
+        // Two plaintexts of different length in the same bucket must produce
+        // identically sized padded payloads (and thus ciphertexts).
+        let short = try NIP44Padding.pad(Data(repeating: 0x41, count: 65))
+        let long = try NIP44Padding.pad(Data(repeating: 0x42, count: 96))
+        #expect(short.count == long.count)
+    }
+
+    @Test func padRejectsOutOfRangePlaintexts() {
+        #expect(throws: (any Error).self) { try NIP44Padding.pad(Data()) }
+        #expect(throws: (any Error).self) { try NIP44Padding.pad(Data(count: 65536)) }
+    }
+
+    @Test func unpadRejectsTamperedLengthPrefix() throws {
+        var padded = try NIP44Padding.pad(Data(repeating: 0x41, count: 40))
+
+        // Claimed length larger than the actual payload
+        var tooLong = padded
+        tooLong[tooLong.startIndex] = 0xFF
+        tooLong[tooLong.startIndex + 1] = 0xFF
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(tooLong) }
+
+        // Claimed length of zero
+        var zero = padded
+        zero[zero.startIndex] = 0x00
+        zero[zero.startIndex + 1] = 0x00
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(zero) }
+
+        // Claimed length whose bucket does not match the payload size
+        // (payload is bucket 64; a claimed length of 20 expects bucket 32)
+        var wrongBucket = padded
+        wrongBucket[wrongBucket.startIndex] = 0x00
+        wrongBucket[wrongBucket.startIndex + 1] = 0x14
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(wrongBucket) }
+
+        // Truncated payloads
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(Data()) }
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(Data([0x00])) }
+        padded.removeLast()
+        #expect(throws: NostrError.invalidCiphertext) { try NIP44Padding.unpad(padded) }
+
+        // Works on Data slices with non-zero startIndex
+        let sliced = try (Data([0xAB]) + NIP44Padding.pad(Data(repeating: 0x41, count: 40))).dropFirst()
+        #expect(try NIP44Padding.unpad(sliced) == Data(repeating: 0x41, count: 40))
+    }
+
+    @Test func paddedEnvelopeRoundTrip_v3() throws {
+        let sender = try NostrIdentity.generate()
+        let recipient = try NostrIdentity.generate()
+        let plaintext = "padded envelope test"
+
+        let ciphertext = try NostrProtocol.encrypt(
+            plaintext: plaintext,
+            recipientPubkey: recipient.publicKeyHex,
+            senderKey: sender.schnorrSigningKey(),
+            padded: true
+        )
+        #expect(ciphertext.hasPrefix("v3:"))
+
+        let decrypted = try NostrProtocol.decrypt(
+            ciphertext: ciphertext,
+            senderPubkey: sender.publicKeyHex,
+            recipientKey: recipient.schnorrSigningKey()
+        )
+        #expect(decrypted == plaintext)
+    }
+
+    @Test func legacyUnpaddedEnvelopeStillDecrypts_v2() throws {
+        let sender = try NostrIdentity.generate()
+        let recipient = try NostrIdentity.generate()
+        let plaintext = "legacy v2 envelope"
+
+        // What deployed clients send today.
+        let ciphertext = try NostrProtocol.encrypt(
+            plaintext: plaintext,
+            recipientPubkey: recipient.publicKeyHex,
+            senderKey: sender.schnorrSigningKey(),
+            padded: false
+        )
+        #expect(ciphertext.hasPrefix("v2:"))
+
+        let decrypted = try NostrProtocol.decrypt(
+            ciphertext: ciphertext,
+            senderPubkey: sender.publicKeyHex,
+            recipientKey: recipient.schnorrSigningKey()
+        )
+        #expect(decrypted == plaintext)
+    }
+
+    @Test func outgoingMessagesStillUseV2UntilRolloutFlagFlips() throws {
+        // Deployed clients reject anything that is not "v2:", so the padded
+        // envelope must stay off by default until decrypt-side support is
+        // widely shipped (see NostrProtocol.sendPaddedEnvelope).
+        #expect(NostrProtocol.sendPaddedEnvelope == false)
+
+        let sender = try NostrIdentity.generate()
+        let recipient = try NostrIdentity.generate()
+        let giftWrap = try NostrProtocol.createPrivateMessage(
+            content: "default envelope",
+            recipientPubkey: recipient.publicKeyHex,
+            senderIdentity: sender
+        )
+        #expect(giftWrap.content.hasPrefix("v2:"))
+    }
+
+    @Test func decryptRejectsUnknownEnvelopeVersion() throws {
+        let sender = try NostrIdentity.generate()
+        let recipient = try NostrIdentity.generate()
+        let ciphertext = try NostrProtocol.encrypt(
+            plaintext: "test",
+            recipientPubkey: recipient.publicKeyHex,
+            senderKey: sender.schnorrSigningKey(),
+            padded: false
+        )
+        let mutated = "v9:" + ciphertext.dropFirst(3)
+        #expect(throws: NostrError.invalidCiphertext) {
+            _ = try NostrProtocol.decrypt(
+                ciphertext: mutated,
+                senderPubkey: sender.publicKeyHex,
+                recipientKey: recipient.schnorrSigningKey()
+            )
+        }
+    }
+
     // MARK: - Helpers
     private static func base64URLDecode(_ s: String) -> Data? {
         var str = s.replacingOccurrences(of: "-", with: "+").replacingOccurrences(of: "_", with: "/")

localPackages/BitFoundation/Sources/BitFoundation/Data+Hex.swift

@@ -8,12 +8,44 @@
 
 import struct Foundation.Data
 
+/// Lowercase hex digits used by `hexEncodedString()`.
+private let hexDigits: [UInt8] = Array("0123456789abcdef".utf8)
+
+/// Maps an ASCII byte to its hex nibble value, or nil for non-hex characters.
+/// Accepts both lowercase and uppercase hex digits.
+@inline(__always)
+private func hexNibble(_ ascii: UInt8) -> UInt8? {
+    switch ascii {
+    case UInt8(ascii: "0")...UInt8(ascii: "9"):
+        return ascii - UInt8(ascii: "0")
+    case UInt8(ascii: "a")...UInt8(ascii: "f"):
+        return ascii - UInt8(ascii: "a") + 10
+    case UInt8(ascii: "A")...UInt8(ascii: "F"):
+        return ascii - UInt8(ascii: "A") + 10
+    default:
+        return nil
+    }
+}
+
 public extension Data {
+    /// Lowercase hex representation of the bytes.
+    ///
+    /// Lookup-table based: this sits on the hot BLE receive path (it is called
+    /// several times per received packet via `PeerID(hexData:)`), where the
+    /// previous per-byte `String(format: "%02x", _)` implementation spent most
+    /// of its time re-parsing the format string through Foundation.
     func hexEncodedString() -> String {
-        if self.isEmpty {
+        if isEmpty {
             return ""
         }
-        return self.map { String(format: "%02x", $0) }.joined()
+        var output = [UInt8](repeating: 0, count: count * 2)
+        var i = 0
+        for byte in self {
+            output[i] = hexDigits[Int(byte >> 4)]
+            output[i + 1] = hexDigits[Int(byte & 0x0F)]
+            i += 2
+        }
+        return String(decoding: output, as: UTF8.self)
     }
 
     /// Initialize Data from a hex string.
@@ -28,28 +60,28 @@ public extension Data {
             hex = String(hex.dropFirst(2))
         }
 
+        let ascii = Array(hex.utf8)
+
         // Reject odd-length strings
-        guard hex.count % 2 == 0 else {
+        guard ascii.count % 2 == 0 else {
             return nil
         }
 
-        // Reject empty strings
-        guard !hex.isEmpty else {
+        // Accept empty strings
+        guard !ascii.isEmpty else {
             self = Data()
             return
         }
 
-        let len = hex.count / 2
-        var data = Data(capacity: len)
-        var index = hex.startIndex
-
-        for _ in 0..<len {
-            let nextIndex = hex.index(index, offsetBy: 2)
-            guard let byte = UInt8(String(hex[index..<nextIndex]), radix: 16) else {
+        var data = Data(capacity: ascii.count / 2)
+        var index = 0
+        while index < ascii.count {
+            guard let high = hexNibble(ascii[index]),
+                  let low = hexNibble(ascii[index + 1]) else {
                 return nil
             }
-            data.append(byte)
-            index = nextIndex
+            data.append((high << 4) | low)
+            index += 2
         }
 
         self = data

localPackages/BitFoundation/Tests/BitFoundationTests/DataHexTests.swift

@@ -0,0 +1,78 @@
+//
+// DataHexTests.swift
+// bitchatTests
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Testing
+import Foundation
+@testable import BitFoundation
+
+struct DataHexTests {
+
+    // MARK: - Encoding
+
+    @Test func encode_knownVectors() {
+        #expect(Data().hexEncodedString() == "")
+        #expect(Data([0x00]).hexEncodedString() == "00")
+        #expect(Data([0x0f]).hexEncodedString() == "0f")
+        #expect(Data([0xf0]).hexEncodedString() == "f0")
+        #expect(Data([0xff]).hexEncodedString() == "ff")
+        #expect(Data([0xde, 0xad, 0xbe, 0xef]).hexEncodedString() == "deadbeef")
+        #expect(Data([0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]).hexEncodedString() == "0123456789abcdef")
+    }
+
+    @Test func encode_allByteValues_matchesFormatReference() {
+        let all = Data((0...255).map { UInt8($0) })
+        let reference = (0...255).map { String(format: "%02x", $0) }.joined()
+        #expect(all.hexEncodedString() == reference)
+    }
+
+    @Test func encode_worksOnDataSlices() {
+        let data = Data([0xaa, 0xde, 0xad, 0xbe, 0xef, 0xbb])
+        let slice = data.dropFirst().dropLast()
+        #expect(slice.hexEncodedString() == "deadbeef")
+    }
+
+    // MARK: - Decoding
+
+    @Test func decode_knownVectors() {
+        #expect(Data(hexString: "deadbeef") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "DEADBEEF") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "DeAdBeEf") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "00") == Data([0x00]))
+        #expect(Data(hexString: "0123456789abcdef") == Data([0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef]))
+    }
+
+    @Test func decode_handlesPrefixAndWhitespace() {
+        #expect(Data(hexString: "0xdeadbeef") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "0XDEADBEEF") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "  deadbeef\n") == Data([0xde, 0xad, 0xbe, 0xef]))
+        #expect(Data(hexString: "") == Data())
+        #expect(Data(hexString: "0x") == Data())
+    }
+
+    @Test func decode_rejectsInvalidInput() {
+        #expect(Data(hexString: "abc") == nil)        // odd length
+        #expect(Data(hexString: "zz") == nil)         // non-hex characters
+        #expect(Data(hexString: "0xg1") == nil)       // non-hex after prefix
+        #expect(Data(hexString: "+f") == nil)         // sign characters are not hex
+        #expect(Data(hexString: "-0") == nil)
+        #expect(Data(hexString: "a\u{00e9}") == nil)  // non-ASCII
+        #expect(Data(hexString: "de ad") == nil)      // interior whitespace
+    }
+
+    // MARK: - Round trip
+
+    @Test func roundTrip_randomLengths() {
+        for length in [0, 1, 2, 3, 8, 16, 31, 32, 33, 64, 255, 1024] {
+            let data = Data((0..<length).map { _ in UInt8.random(in: .min ... .max) })
+            let hex = data.hexEncodedString()
+            #expect(hex.count == length * 2)
+            #expect(Data(hexString: hex) == data)
+            #expect(Data(hexString: hex.uppercased()) == data)
+        }
+    }
+}