When working with OpenVPN, the "TLS Error: local/remote TLS keys are out of sync" message typically indicates a breakdown in the cryptographic handshake between client and server. This often occurs after network interruptions or system sleep cycles, where the control channel's sequence numbers become misaligned.

The error manifests when:

• Packet retransmissions occur during unstable connections
• System sleep/hibernation interrupts active VPN sessions
• Server-side TLS renegotiation thresholds are reached
• Client and server lose cryptographic state synchronization

For a Windows client configuration (like in the Vista VM mentioned), modify your .ovpn file with these technical adjustments:

client
dev tun
remote vpn.riseup.net 1194
proto udp
resolv-retry infinite
nobind
persist-key
persist-tun
auth-user-pass
ca RiseupCA.pem
comp-lzo no
verb 4
reneg-sec 0
keepalive 10 60
tls-client
remote-cert-tls server

<ca>
-----BEGIN CERTIFICATE-----
[Certificate contents here]
-----END CERTIFICATE-----
</ca>

These additions specifically address the sync issue:

• reneg-sec 0: Disables TLS renegotiation (common cause of sync loss)
• keepalive 10 60: Maintains connection state during inactivity
• persist-key/persist-tun: Preserves cryptographic state across restarts

When basic fixes fail, try these developer-level approaches:

1. Capture network traffic with Wireshark (filter: udp.port == 1194)
2. Enable OpenVPN's verbosity to 6 for detailed crypto analysis
3. Compare TLS handshake timestamps between client/server logs

If you control the server (like a private OpenVPN instance), add these to server.conf:

tls-timeout 120
push "persist-key"
push "persist-tun"
tls-version-min 1.2

For persistent issues, implement this PowerShell watchdog script:

while ($true) {
    $status = & "C:\Program Files\OpenVPN\bin\openvpn.exe" --config "client.ovpn" --service exit-event 0
    if ($LASTEXITCODE -eq 0) { break }
    Write-Host "TLS sync error detected, restarting VPN..."
    Start-Sleep -Seconds 30
}

After implementing fixes:

1. Verify time synchronization (TLS relies on accurate timestamps)
2. Check for MTU mismatches with ping tests
3. Confirm no intermediate devices are altering packets

When dealing with OpenVPN connections, the TLS key synchronization mechanism is crucial for maintaining a secure tunnel. The error message you're encountering indicates a breakdown in this synchronization process between your client and Riseup's VPN server. Here's what's happening under the hood:

// Simplified OpenVPN key exchange sequence
1. Client Hello → Server
2. Server Hello → Client  
3. Key Exchange (DH params)
4. Finished Messages
5. Data Transmission

The key synchronization failure typically occurs when:

• The TCP/UDP session was interrupted (like during sleep mode)
• Packet retransmissions exceeded tolerance thresholds
• Session state wasn't properly maintained
• Network address translation (NAT) caused issues

Based on the original config, try this enhanced version:

client
dev tun
proto tcp
remote vpn.riseup.net 1194
resolv-retry infinite
nobind
persist-key
persist-tun
tls-client
remote-cert-tls server
auth-user-pass
ca RiseupCA.pem
cipher AES-256-CBC
auth SHA256
tls-version-min 1.2
tls-cipher TLS-ECDHE-ECDSA-WITH-AES-256-GCM-SHA384
reneg-sec 0
verb 4

<ca>
-----BEGIN CERTIFICATE-----
[Your CA Certificate Here]  
-----END CERTIFICATE-----
</ca>

For Windows Vista VMs, these registry tweaks might help:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"TcpMaxDataRetransmissions"=dword:00000010
"TCPTimedWaitDelay"=dword:0000001e

Create a batch script to handle reconnections:

@echo off
:start
openvpn.exe --config riseup.ovpn
ping -n 5 127.0.0.1 > nul
goto start

After implementing changes, verify with:

1. netstat -ano | findstr ESTABLISHED
2. route print to check VPN routes
3. Packet capture with Wireshark (filter: tcp.port == 1194)