Authenticate private media capabilities in Noise

bitchat/Protocols/BitchatProtocol.swift

@@ -83,6 +83,11 @@ enum NoisePayloadType: UInt8 {
     // Android client. The complete BitchatFilePacket is encrypted inside
     // Noise before the outer noiseEncrypted packet is fragmented.
     case privateFile = 0x20
+    // Versioned peer state authenticated by the surrounding Noise session.
+    // This is intentionally distinct from the public announce: announce
+    // capabilities are discovery hints, while this payload proves possession
+    // of the advertised Noise static key before downgrade state is pinned.
+    case authenticatedPeerState = 0x21
     // Verification (QR-based OOB binding)
     case verifyChallenge = 0x10     // Verification challenge
     case verifyResponse  = 0x11     // Verification response
@@ -112,6 +117,7 @@ enum NoisePayloadType: UInt8 {
         case .groupKeyUpdate: return "groupKeyUpdate"
         case .voiceFrame: return "voiceFrame"
         case .privateFile: return "privateFile"
+        case .authenticatedPeerState: return "authenticatedPeerState"
         case .verifyChallenge: return "verifyChallenge"
         case .verifyResponse: return "verifyResponse"
         case .vouch: return "vouch"

bitchat/Protocols/Packets.swift

@@ -156,6 +156,89 @@ struct AnnouncementPacket {
     }
 }
 
+/// State that is authoritative only because it is carried inside an
+/// established Noise session. The public announce remains useful for
+/// discovery, but its self-signature cannot prove possession of the copied
+/// Noise public key it contains.
+///
+/// Wire format (v1):
+/// `[version=0x01][type][length][value]...`
+/// - TLV `0x01`: canonical minimal little-endian `PeerCapabilities`
+/// - TLV `0x02`: 32-byte Ed25519 signing public key
+///
+/// Unknown TLVs are skipped for forward compatibility. Unknown versions,
+/// duplicates, non-canonical capability fields, and malformed lengths are
+/// rejected without changing authenticated state.
+struct AuthenticatedPeerStatePacket: Equatable {
+    static let currentVersion: UInt8 = 1
+    static let signingPublicKeyLength = 32
+
+    let capabilities: PeerCapabilities
+    let signingPublicKey: Data
+
+    private enum TLVType: UInt8 {
+        case capabilities = 0x01
+        case signingPublicKey = 0x02
+    }
+
+    func encode() -> Data? {
+        guard signingPublicKey.count == Self.signingPublicKeyLength else { return nil }
+        let capabilityBytes = capabilities.encoded()
+        guard !capabilityBytes.isEmpty, capabilityBytes.count <= 8 else { return nil }
+
+        var data = Data([Self.currentVersion])
+        data.append(TLVType.capabilities.rawValue)
+        data.append(UInt8(capabilityBytes.count))
+        data.append(capabilityBytes)
+        data.append(TLVType.signingPublicKey.rawValue)
+        data.append(UInt8(signingPublicKey.count))
+        data.append(signingPublicKey)
+        return data
+    }
+
+    static func decode(from data: Data) -> AuthenticatedPeerStatePacket? {
+        guard data.first == Self.currentVersion else { return nil }
+
+        var offset = 1
+        var capabilities: PeerCapabilities?
+        var signingPublicKey: Data?
+
+        while offset < data.count {
+            guard offset + 2 <= data.count else { return nil }
+            let typeRaw = data[offset]
+            let length = Int(data[offset + 1])
+            offset += 2
+            guard offset + length <= data.count else { return nil }
+            let value = Data(data[offset..<(offset + length)])
+            offset += length
+
+            guard let type = TLVType(rawValue: typeRaw) else {
+                continue
+            }
+            switch type {
+            case .capabilities:
+                guard capabilities == nil,
+                      !value.isEmpty,
+                      value.count <= 8 else { return nil }
+                let decoded = PeerCapabilities(encoded: value)
+                guard decoded.encoded() == value else { return nil }
+                capabilities = decoded
+
+            case .signingPublicKey:
+                guard signingPublicKey == nil,
+                      value.count == Self.signingPublicKeyLength else { return nil }
+                signingPublicKey = value
+            }
+        }
+
+        guard let capabilities, let signingPublicKey else { return nil }
+        return AuthenticatedPeerStatePacket(
+            capabilities: capabilities,
+            signingPublicKey: signingPublicKey
+        )
+    }
+}
+
 struct PrivateMessagePacket {
     let messageID: String
     let content: String