🪐 The Secret Meeting Room
Secure Group Chat with Multiple Layers
In 20 minutes: Real-world group messaging tutorial
Prerequisite: Basic AES encryption
🎯 The Simple Story
Alice, Bob, and Charlie want a secure group chat.
Problem: Messages sent over the internet, can Eve read them?
Solution: Multiple layers of protection:
Message: "Meet at 5pm"
Layer 1 (AES): "Meet at 5pm" → "x7k!m$#L"
Layer 2 (Signal): "x7k!m$#L" → "$9x!mL#k7"
Layer 3 (MLS): "Meet at 5pm" → "Z$mk!7xL$"
Layer 4 (DK): "Z$mk!7xL$" → "P!z$#mL"
Eve sees: "P!z$#mL"
Eve tries: "I don't have Alice's password + Bob's ratchet + Group secrets!"
Result: "P!z$#mL" = Gibberish! Eve gives up!
🧠 Mental Model
Hold this picture in your mind:
Secure Group Chat (Nested Protection):
Layer 4 (Outermost): DH Handshake
├─ "Alice and Bob agree on a secret"
├─ "Only their devices can derive this"
└─ Eve doesn't have either device!
Layer 3: MLS (Meeting Room):
├─ "Alice, Bob, Charlie can all chat together"
├─ "Group secret known only to members"
└─ "Eve can't join the meeting room!"
Layer 2: Signal (Phone Booth):
├─ "Every message gets a new key"
├─ "Old keys deleted (forward secrecy)!"
└─ "Eve can't read old messages!"
Layer 1 (Innermost): AES (Safe Deposit):
├─ "Each message also has password protection"
└─ "Eve would need every message's password!"
Result: Like a castle with moat + guards + safe!
📊 How It Works Together
Why all these layers?
- AES (innermost): Final password protection
- Signal (middle): Forward secrecy for messages
- MLS (middle): Group membership and context
- DH (outermost): Initial key establishment
🎭 The Story: Castle with Multiple Defenses
Eve wants to read Alice, Bob, and Charlie's conversation:
Castle Defense System
Eve's Attack 1: Try just reading
Castle says:
❌ Outer Lock: DH (need devices!)
Even if Eve has Alice's phone → DH protects without her phone!
Eve's Attack 2: Try intercepting messages
Castle says:
❌ Layer 2 Signal: Forward secrecy!
Even if Eve steals phone after message → Key deleted!
Eve's Attack 3: Try joining the group
Castle says:
❌ Layer 3 MLS: Group access!
Eve isn't a member → Can't read!
Eve's Attack 4: Stealing encrypted messages
Castle says:
❌ Layer 1 AES: Password needed!
Eve doesn't have Alice's every password!
Defense in Depth
Layer 1 (AES): 1 in 100 chance to break
Layer 2 (Signal): 1 in 1,000 chance to break
Layer 3 (MLS): 1 in 1,000,000 chance to break
Layer 4 (DH): 1 in 1,000,000,000 chance to break
Eve's chances to break ALL layers:
1/100 × 1/1,000 × 1/1,000,000 × 1/1,000,000
= 1/1,000,000,000,000,000,000
That's 1 in a QUADRILLION!
Even if Eve breaks one layer...
Scenario: Quantum computer breaks AES
Ciphertext: "P!z$#mL"
↓
Eve quantum computer attacks: BREAKS AES!
↓
Eve still needs: Signal + MLS + DH...
Still protected:
❌ Signal (forward secrecy)
❌ MLS (group access)
❌ DH (devices)
⚙️ Setting Up Multiple Layers
Complete Example
import {
CascadingCipherManager,
AESCipherLayer,
DHCipherLayer,
SignalCipherLayer,
MLSCipherLayer
} from "cryptography/CascadingCipher";
// 1. Create manager
const manager = new CascadingCipherManager();
// 2. Add layers in ORDER (bottom-to-top):
// AES first (simple, no dependencies)
manager.addLayer(new AESCipherLayer());
// DH second (key exchange)
const dhLayer = new DHCipherLayer();
dhLayer.initialize({
aliceKey: aliceDHKeyPair.privateKey,
bobKey: bobDHKeyPair.privateKey
});
manager.addLayer(dhLayer);
// Signal third (forward secrecy)
const signalWasm = await loadSignalWasm();
const signalState = await createDoubleRatchetState();
manager.addLayer(new SignalCipherLayer(signalWasm, signalState));
// MLS fourth (group security)
const mlsManager = new MLSManager("alice@example.com");
await mlsManager.initialize();
await mlsManager.createGroup("team-chat");
manager.addLayer(new MLSCipherLayer(mlsManager, "team-chat"));
Encrypting a Message
// Bob wants to send: "Meeting at 5pm"
const message = "Meeting at 5pm";
const plaintext = new TextEncoder().encode(message);
const keys = {
"AES-GCM-256": { password: "my-password" },
"DH-AES-GCM": {
privateKey: aliceDHKeyPair.privateKey,
publicKey: bobDHKeyPair.publicKey
},
"X3DH-DoubleRatchet": { doubleRatchetState },
"ML": { mlsManager, groupId: "team-chat" }
};
// CASCADING ENCRYPTION HAPPENS HERE!
const encrypted = await manager.encrypt(plaintext, keys);
Decrypting a Message
// Charlie receives the message
const keys = {
"AES-GCM-256": { /* all the same keys */ },
"DH-AES-GCM": { /* all the same keys */ },
"X3DH-DoubleRatchet": { /* all the same keys */ },
"ML": { mlsManager, groupId: "team-chat" }
};
// CASCADING DECRYPTION HAPPENS HERE!
const decrypted = await manager.decrypt(encrypted, keys);
const message = new TextDecoder().decode(decrypted);
// "Meeting at 5pm"
🎮 Try It Yourself
Details
Question 1: What's the order of decryption for AES + Signal + MLS?
Answer: REVERSE of encryption! Since encryption was AES → Signal → MLS, decryption is MLS⁻¹ → Signal⁻¹ → AES⁻¹. You can't decrypt AES first because Signal still scrambled the message! So: MLS → Signal → AESQuestion 2: If Eve steals Charlie's phone, how many layers does she need to break?
Answer: Even if Eve has Charlie's phone, she would need:
- Charlie's AES password (she might guess it!)
- Charlie's DH private key AND Bob's DH private key
- Charlie's and Bob's Signal double ratchet states
- Charlie's and Bob's MLS group secrets
That's 4 layers to break. And even if she gets 1, 2, or 3 layers broken, layer 4 might still protect the message (like the quantum-resistant DH layer)!
Question 3: What happens to the conversation if Eve breaks one layer but not any others?
Answer: It depends WHICH layer!
If Eve breaks the innermost (AES): She can read raw messages but only the ones without additional layers! If the message has 4 layers and she breaks AES but not the other 3 layers, the data she gets is still scrambled by Signal + MLS + DH. She has the message body ("Meeting at 5pm") but can't make sense of it because it's still encrypted by layers 2, 3, and 4!
If Eve breaks just Signal but not AES/MLS/DH: They can read plaintext from AES but without double ratchet keys they can't understand which message belongs to which ratchet!
If Eve breaks MLS but not AES/Signal/DH: They can decrypt DH but not the group structure of MLS, so they can read messages but not know WHO sent them!
Each layer protects different things, but they're all needed together for complete security!
💡 Real-World Scenario: Corporate Messaging
Scenario: Company uses cascading cipher for secure internal messages
Threats:
- Quantum computers breaking AES in the future
- Current attacks on Signal's double ratchet
- Compromised MLS groups
- Malicious insider compromising passwords
Cascading cipher provides:
Quantum resistance: ML-KEM to protect from future threats
Forward secrecy: Signal protects from key exposure after compromise
Group membership: MLS protects from unauthorized members joining
Password protection: AES protects against weak passwords
Key establishment: DH protects the initial key exchange
Result: Breach in one layer ≠ Breach of all!
✅ Quick Check
**Can you explain defense in depth to a 5-year-old?
Try saying this out loud:
"A lockbox is good, but a lockbox inside a safe, inside a vault, inside a fortress with multiple guards is even better! Even if someone breaks ONE lock, they still have 3 MORE to break! That's why we use cascade layers. Breaking one doesn't break everything!"
🎓 Key Takeaways
✅ Multiple layers = Defense in depth
✅ Each layer protects differently = Compromise in one ≠ All!
✅ Order matters = Encrypt AES→Signal→MLS, Decrypt MLS⁻¹→Signal⁻¹→AES⁻¹
✅ Quantum-resistant layers = Future-proof your data
✅ Forward secrecy = Past messages stay secret
✅ Group access = Only members can join the chat
✅ Compromise resilience = One layer broken ≠ game over
🎉 What You'll Learn Next
Now you know how to build a secure group chat! But there's more:
We'll add ML-KEM for quantum protection - the ultimate layer!
Now you can build secure group chats. Next: Maximum security with quantum protection!