Camera, screen and clipboard leaks

Most of this manual is about where a seed phrase rests. This page is about the few minutes when it moves: the moment a wallet shows you the words, the moment you write them, the moment you type them back in. Nearly every leak that isn't a phish or a wrench happens in one of those windows, and the fix is to make the window short and to know what's watching it.

The screen

A seed phrase on a screen is readable by anything that can see the screen.

• The webcam above the display, and the phone camera on the desk, both of which can be turned on by software you didn't install on purpose.
• The security camera in the corner of the room, the doorbell camera facing the hall, the baby monitor. Home cameras upload to someone's cloud by default.
• The window behind you, the glass of a framed picture, the reflection in your own glasses on a video call.
• Screen-sharing and remote-support software, which sees exactly what you see.
• The operating system's own screenshot and "recent activity" features, which on some systems save what was on screen without asking.

Hardware wallets show the words on their own small screen for this reason: it is a screen nothing else can read. Use it. A seed generated on a laptop display has been shown to the laptop, and the laptop is the least trustworthy thing in the room.

The camera, on purpose

"I'll just take a photo so I don't lose it." The photo goes into the camera roll, the camera roll syncs to a cloud account, the cloud account has a password that has been in a breach, and the photo is also in the backup, the shared album, and the thumbnail cache. From then on the seed is on the device, which is what a border search or a stolen phone finds first.

The same applies to a screenshot, a scan, and a photo of the metal plate "for the records." If you need a record, write the cipher numbers on paper. A photograph of a column of prices on a receipt leaks nothing, as long as the cipher's name and the passphrase aren't in the same album.

The keyboard

Typing a seed into a computer gives it to the keyboard driver, the operating system, every program with permission to read keystrokes, the browser if it's a web page, and the cloud if the browser syncs form history. A keylogger doesn't need to be exotic; the one Joanna Rutkowska demonstrated in 2009 was installed in two minutes from a USB stick on a laptop left in a hotel room.

Rules for the keyboard:

1. The only legitimate place to type a seed is into the signing device that will hold it, during a restore you chose to do, and that device shouldn't be a general-purpose computer.
2. If you must use a computer, use one that is offline and will be wiped, and type the words, never paste them.
3. Software wallets on a phone are a compromise. If you use one, it holds a small amount, and its seed is not the seed of the long-term wallet.

We will never ask for a seed word or a passphrase. Never type one into this site or any tool it links to.

The clipboard

The clipboard is the quietest leak of all. Anything you copy is readable by every program on the machine, and on some systems it syncs to your other devices and to the cloud.

Two things get copied: seed words, and addresses. Copying seed words is the keyboard problem again, worse. Copying addresses has its own attacker. In March 2023 Kaspersky described malware spread in fake Tor Browser installers that did nothing except watch the Windows clipboard; when a bitcoin address appeared, it was swapped for the attacker's. It made no network connections and showed no sign of itself. Nearly 16,000 people in 52 countries sent coins to the wrong address before it was found, about $400,000 in all.

The defence costs five seconds: read the address on the signing device's own screen and compare the first and last characters with what the computer shows, every time you send. The cipher pages are built so that nothing needs copying: you read the number for each word with your eyes and write it with a pencil.

The printer

A printed seed has been through a printer's memory, and office printers keep a copy of recent jobs on their disk. Home inkjets are less of a problem, but the PDF you printed from is still in the downloads folder, the print spool, and the cloud if documents sync. If paper is the plan, write by hand.

The room

Put the leaks together and the picture of a safe setup is a plain one:

• Generate and show the seed on a device with its own screen, in a room with no cameras, your back to a wall, phone in another room.
• Write the cipher numbers by hand, on paper, from the tome you downloaded earlier. The encode page is a lookup table you read; nothing gets typed.
• Never photograph, screenshot, print, type or paste the words. Not once, not "just for now."
• Check the restore on the signing device, then fund the wallet.

If a window was open

If the words were on a laptop screen, in a photo, on a clipboard, or typed into anything other than the signer, assume they are copied. Make a new seed on the signing device, move the funds, and do the next one properly. The cost of a new seed is an afternoon. The cost of hoping is the wallet.

Sources