> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/mullvad/mullvadvpn-app/llms.txt
> Use this file to discover all available pages before exploring further.

# Quantum-Resistant Tunnels

> Post-quantum cryptography using ephemeral pre-shared keys (PSK) to protect against future quantum computer attacks

## Overview

Quantum-resistant tunnels add an additional layer of encryption to WireGuard connections using post-quantum cryptography. This protects your VPN traffic from potential future attacks by quantum computers that could break current encryption algorithms.

Mullvad implements quantum resistance through **ephemeral pre-shared keys (PSK)** negotiated using post-quantum key encapsulation mechanisms (KEM).

<Note>
  Quantum-resistant tunnels are available on all platforms: Windows, Linux, macOS, Android, and iOS.
</Note>

## How It Works

### Traditional WireGuard Encryption

Standard WireGuard uses:

* **Curve25519**: Elliptic curve cryptography for key exchange
* **ChaCha20-Poly1305**: Symmetric encryption

These algorithms are secure today but could potentially be broken by quantum computers in the future.

### Quantum-Resistant Enhancement

Mullvad adds a quantum-resistant layer:

1. **Post-Quantum KEM**: Generates ephemeral key pairs using post-quantum algorithms
2. **PSK Exchange**: Securely negotiates a pre-shared key with the relay server
3. **WireGuard PSK**: The negotiated key is used as WireGuard's pre-shared key field
4. **Hybrid Security**: Combined classical (Curve25519) + post-quantum cryptography

```
┌─────────────────────────────────────────────────────┐
│   Application Data (Your Internet Traffic)          │
└─────────────────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────┐
│   WireGuard Encryption (ChaCha20-Poly1305)          │
│   + Pre-Shared Key (Post-Quantum)                   │
└─────────────────────────────────────────────────────┘
                      │
                      ▼
┌─────────────────────────────────────────────────────┐
│   Curve25519 Key Exchange (Classical)               │
└─────────────────────────────────────────────────────┘
```

<Info>
  This "hybrid" approach provides security even if either the classical or post-quantum algorithm is compromised.
</Info>

## Key Exchange Process

### Ephemeral PSK Negotiation

The PSK is never persisted to disk and is regenerated for each tunnel:

1. **Key Generation**: Client generates post-quantum KEM key pairs
2. **Request**: Client sends public key to relay server via TLS 1.3
3. **Encapsulation**: Server generates shared secret and encapsulates it
4. **Response**: Server returns encapsulated secret
5. **Decapsulation**: Client decapsulates to derive shared secret
6. **PSK Derivation**: Shared secret becomes WireGuard PSK

<Warning>
  The PSK is stored in memory only and is never written to disk. It's automatically zeroized when the tunnel is torn down.
</Warning>

## Enabling Quantum-Resistant Tunnels

### Using the GUI

<Steps>
  <Step title="Open Settings">
    Launch Mullvad VPN and navigate to **Settings** → **VPN settings**
  </Step>

  <Step title="Enable Quantum Resistance">
    Find the **Quantum-resistant tunnel** option and toggle it **On**
  </Step>

  <Step title="Reconnect">
    The app will automatically reconnect with quantum-resistant encryption enabled
  </Step>
</Steps>

### Using the CLI

```bash theme={null}
# Enable quantum-resistant tunnels
mullvad relay set tunnel wireguard quantum-resistant on

# Disable quantum-resistant tunnels
mullvad relay set tunnel wireguard quantum-resistant off

# Check current setting
mullvad relay get
```

### Verify It's Active

When connected with quantum resistance enabled:

```bash theme={null}
mullvad status -v
```

You should see:

```
Connected to ...
Quantum resistant: yes
```

The connection panel in the GUI will also display a quantum resistance indicator.

## Performance Impact

### Connection Establishment

* **Slight increase in connection time**: Additional PSK negotiation adds \~100-200ms
* **Key generation**: Post-quantum key pair generation takes a few milliseconds

### Ongoing Connection

* **No throughput impact**: Once established, performance is identical to standard WireGuard
* **No additional CPU overhead**: PSK is used in existing WireGuard encryption

<Info>
  The performance impact is minimal and only affects the initial connection. Once connected, there's no difference in speed or bandwidth.
</Info>

## Security Properties

### Threat Model

Quantum-resistant tunnels protect against:

* **Store-now-decrypt-later attacks**: Adversaries recording encrypted traffic today to decrypt with future quantum computers
* **Future quantum cryptanalysis**: Breaks in classical ECC algorithms

### Cryptographic Algorithms

Mullvad uses NIST-approved post-quantum algorithms for KEM:

* Post-quantum key encapsulation mechanisms
* Hybrid construction combining classical and post-quantum security

### Limitations

<Warning>
  **Does not protect against:**

  * Traffic analysis (see [DAITA](/features/daita))
  * Correlation attacks on VPN servers
  * Compromise of the Mullvad service itself
  * Local device compromise
</Warning>

## Compatibility with Other Features

Quantum-resistant tunnels work with:

* ✅ [WireGuard multihop](/features/multihop)
* ✅ [DAITA](/features/daita)
* ✅ [Obfuscation protocols](/features/obfuscation) (TCP, Shadowsocks, QUIC)
* ✅ [Split tunneling](/features/split-tunneling)
* ✅ [Custom DNS](/features/custom-dns)
* ✅ [Content blockers](/features/content-blockers)

### Example: Quantum-Resistant Multihop

```bash theme={null}
# Enable quantum resistance with multihop
mullvad relay set tunnel wireguard quantum-resistant on
mullvad relay set tunnel wireguard use-multihop on
```

## Technical Details

### PSK Storage

From the source code (talpid-types/src/net/wireguard.rs:295-306):

```rust theme={null}
/// A WireGuard preshared key (PSK). Used to make the tunnel quantum-resistant.
#[derive(Clone, PartialEq, Eq, Hash, Zeroize, ZeroizeOnDrop)]
pub struct PresharedKey(Box<[u8; 32]>);
```

* PSK is 32 bytes (256 bits)
* Automatically zeroized on drop (secure memory cleanup)
* Never serialized or deserialized to disk

### Key Rotation

PSKs are ephemeral:

* New PSK negotiated for each tunnel connection
* PSK is discarded when tunnel disconnects
* No persistent key storage

## Troubleshooting

### Connection Failures

If quantum-resistant connections fail:

1. **Check server support**: Ensure selected relay supports quantum resistance
2. **Network connectivity**: PSK exchange requires API connectivity
3. **Firewall rules**: Ensure HTTPS (443) to Mullvad API is allowed
4. **Temporary disable**: Try disabling quantum resistance to isolate the issue

### Verification

```bash theme={null}
# Check if quantum resistance is active
mullvad status -v | grep -i quantum

# View tunnel configuration
mullvad relay get
```

## Migration from Legacy Settings

Older Mullvad versions used `use_pq_safe_psk` setting:

* Automatically migrated to `quantum_resistant` in newer versions
* `auto` setting means enabled by default
* Settings persist across app updates

## Best Practices

<Tabs>
  <Tab title="Maximum Security">
    Enable all quantum-resistant features:

    ```bash theme={null}
    mullvad relay set tunnel wireguard quantum-resistant on
    mullvad relay set tunnel wireguard use-multihop on
    mullvad tunnel set tunnel wireguard daita on
    ```
  </Tab>

  <Tab title="Performance Optimized">
    Enable quantum resistance without multihop:

    ```bash theme={null}
    mullvad relay set tunnel wireguard quantum-resistant on
    mullvad relay set tunnel wireguard use-multihop off
    ```
  </Tab>
</Tabs>

## Further Reading

* [Mullvad's Post-Quantum Blog Announcement](https://mullvad.net/en/blog/tag/post-quantum)
* [NIST Post-Quantum Cryptography Standardization](https://csrc.nist.gov/projects/post-quantum-cryptography)
* [WireGuard PSK Documentation](https://www.wireguard.com/)

## Related Features

* [WireGuard Protocol](/features/wireguard) - Base VPN protocol
* [Multihop](/features/multihop) - Route through multiple servers
* [DAITA](/features/daita) - Defeat traffic analysis
* [Obfuscation](/features/obfuscation) - Bypass VPN blocking