Fix encryption key exchange and add persistent identity for favorites

- Implement three-tier key system: ephemeral encryption, ephemeral signing, persistent identity
- Fix signature verification by properly separating KeyAgreement and Signing keys
- Add persistent identity key for favorites that survives app restarts
- Fix Data subscript crashes by converting to byte arrays
- Add proper error handling for key exchange
- Private messages remain fully encrypted with ephemeral keys

bitchat/Protocols/BinaryProtocol.swift

@@ -185,7 +185,6 @@ extension BitchatMessage {
         // - Recipient nickname length + data
         // - Sender peer ID length + data
         // - Mentions array
-        // - Voice note duration (8 bytes, double) + data length (4 bytes) + data
         
         var flags: UInt8 = 0
         if isRelay { flags |= 0x01 }
@@ -194,7 +193,6 @@ extension BitchatMessage {
         if recipientNickname != nil { flags |= 0x08 }
         if senderPeerID != nil { flags |= 0x10 }
         if mentions != nil && !mentions!.isEmpty { flags |= 0x20 }
-        if voiceNoteData != nil { flags |= 0x40 }
         
         data.append(flags)
         
@@ -261,24 +259,6 @@ extension BitchatMessage {
             }
         }
         
-        // Voice note data
-        if let voiceData = voiceNoteData, let duration = voiceNoteDuration {
-            // Duration as 8 bytes (double)
-            let durationBits = duration.bitPattern
-            for i in (0..<8).reversed() {
-                data.append(UInt8((durationBits >> (i * 8)) & 0xFF))
-            }
-            
-            // Voice data length as 4 bytes (UInt32)
-            let voiceLength = UInt32(min(voiceData.count, Int(UInt32.max)))
-            for i in (0..<4).reversed() {
-                data.append(UInt8((voiceLength >> (i * 8)) & 0xFF))
-            }
-            
-            // Voice data
-            data.append(voiceData.prefix(Int(voiceLength)))
-        }
-        
         return data
     }
     
@@ -304,7 +284,6 @@ extension BitchatMessage {
         let hasRecipientNickname = (flags & 0x08) != 0
         let hasSenderPeerID = (flags & 0x10) != 0
         let hasMentions = (flags & 0x20) != 0
-        let hasVoiceNote = (flags & 0x40) != 0
         
         // Timestamp
         guard offset + 8 <= dataCopy.count else { 
@@ -402,31 +381,6 @@ extension BitchatMessage {
             }
         }
         
-        // Voice note data
-        var voiceNoteData: Data?
-        var voiceNoteDuration: TimeInterval?
-        if hasVoiceNote && offset + 12 <= dataCopy.count {
-            // Duration (8 bytes)
-            let durationData = dataCopy[offset..<offset+8]
-            let durationBits = durationData.reduce(0) { result, byte in
-                (result << 8) | UInt64(byte)
-            }
-            voiceNoteDuration = TimeInterval(bitPattern: durationBits)
-            offset += 8
-            
-            // Voice data length (4 bytes)
-            let lengthData = dataCopy[offset..<offset+4]
-            let voiceLength = lengthData.reduce(0) { result, byte in
-                (result << 8) | UInt32(byte)
-            }
-            offset += 4
-            
-            // Voice data
-            if offset + Int(voiceLength) <= dataCopy.count {
-                voiceNoteData = dataCopy[offset..<offset+Int(voiceLength)]
-            }
-        }
-        
         let message = BitchatMessage(
             sender: sender,
             content: content,
@@ -436,9 +390,7 @@ extension BitchatMessage {
             isPrivate: isPrivate,
             recipientNickname: recipientNickname,
             senderPeerID: senderPeerID,
-            mentions: mentions,
-            voiceNoteData: voiceNoteData,
-            voiceNoteDuration: voiceNoteDuration
+            mentions: mentions
         )
         return message
     }