How to Exchange Contacts

Step-by-step guide for exchanging contact cards with other Vauchi users.

A handshake is a security check we stopped noticing centuries ago: you confirm someone is real, present, and willing, all in one gesture. A Vauchi exchange is the same idea wearing newer clothes. The simplest version — and the one this guide walks through — is two phones showing each other a QR code while you stand close enough to read them.

Prerequisites

  • Both you and the other person have Vauchi installed
  • For the in-person QR exchange below: both devices have working cameras
  • You don't strictly need both at once — see Other ways to exchange if you're not in the same room

QR Code Exchange

Both people show and scan each other's QR codes. Every exchange uses fresh keys, so the past stays private even if a key later leaks (forward secrecy). The QR itself carries only the person's public key and a one-time token — nothing secret, and it goes stale after five minutes.

Step 1: Open Exchange

  1. Open Vauchi
  2. Tap the Exchange tab at the bottom

Step 2: Show Your QR Code

  1. Tap Show My QR Code
  2. A QR code appears on your screen
  3. Show it to the other person

Tip

Keep your screen brightness up and hold steady for easier scanning.

Step 3: They Scan Your Code

  1. The other person points their camera at your QR code
  2. Their device confirms a successful scan

Step 4: Scan Their Code

  1. Tap Scan QR Code
  2. Point your camera at their QR code
  3. Wait for the scan to complete

Step 5: Confirm

Both devices show "Exchange Successful"

You now have each other's contact cards.

Info

On iOS, "physically together" isn't taken on trust: the two devices play a brief ultrasonic handshake (~18–20 kHz, audible to the dog and no one else) to confirm they're within about three metres. If the tone doesn't carry, it falls back to a manual confirmation tap. Android proximity checking is planned; desktop, CLI, and TUI confirm manually.

Other ways to exchange

QR is the default because it works on every platform and needs nothing but a camera. But proximity has more than one shape, and Vauchi offers a few:

ModeHow it worksBest for
QR (default)Show and scan codesAnywhere, any device
TapHold phones together (NFC)Quick face-to-face swaps
BumpBump or shake the devices (BLE + motion)Crowded rooms, no line of sight
LinkShare a one-off vauchi://exchange?… URLPeople who aren't in the room

The first three all prove you were in the same place at the same time, which is the strongest defence against a stranger quietly inserting themselves into the middle of your exchange. Link mode relaxes that proof in return for reach: you send a single-use URL, and the exchange finishes asynchronously through the relay over the following days. It's the difference between a handshake and a sealed letter — both work, one knows the room was empty.

Troubleshooting

QR Code Won't Scan

  1. Lighting: Make sure the QR code is well-lit
  2. Stability: Hold both devices steady
  3. Distance: Try moving closer or farther
  4. Clean lens: Wipe your camera lens
  5. Refresh: Generate a new QR code (they expire after 5 minutes)

Exchange Keeps Failing

  1. Check internet connectivity on both devices
  2. Ensure the QR code hasn't expired (5-minute limit)
  3. Restart the app on both devices
  4. Try a fresh QR code

After Exchange

Once exchange completes:

  • They appear in your Contacts list
  • You can see their card (fields they've shared)
  • They can see your card (fields you've shared)
  • Future changes sync automatically

Next Steps

Security Notes

  • QR codes expire after 5 minutes (replay protection)
  • Both parties must scan each other's QR codes (mutual verification)
  • Each exchange uses fresh ephemeral keys (forward secrecy)
  • Exchange uses encrypted key agreement
  • The relay is a blind courier: it forwards encrypted blobs, routes them with daily-rotating mailbox tokens rather than your identity, and never learns your IP address (Oblivious HTTP). It carries the envelope; it cannot read the letter.

For more on security, see Encryption.