How to transfer files from an air-gapped or offline computer

Six ways exist, from a USB key to a data diode. The right one depends less on technology than on three questions: how much you move, how often, and who in your organisation must approve the flow.

See the price and start Watch the proof

€79 / monthbilled yearly (€948), or €99 monthly; 14-day money-back guarantee
≈ 5 kB/s5 MB of logs ≈ 2 min 23 s per loop on a full-HD screen (estimate yours)
Nothing to installone HTML file on the offline PC, and a camera you are allowed to use

Start with the question that decides everything

An air gap is a security decision, not an accident. Before choosing a tool, find out what your organisation allows to leave the machine and through which channel. In regulated settings (critical infrastructure under NIS2, banks under DORA, plants following IEC 62443) a flow out of an isolated system is usually treated as an interconnection to authorise and log, whatever the medium.

If nobody can authorise the transfer, the answer is not a better tool: it is to not move the file. Every method below assumes the content is yours to move.

1. A USB key under a media policy

The fastest and most familiar route. Many organisations ban it, or allow it only through registered keys, encryption and a scanning station, because removable media are a well-known way for malware to reach isolated networks. If your policy offers a sanctioned USB path, it is the right answer for large volumes. See Bouraq vs USB keys.

2. Write-once media: CD or DVD

A disc burned once cannot be rewritten afterwards, which limits what it can carry, and some security teams prefer it to USB for that reason. It needs a burner on the offline PC, discs, and someone to track them; it suits occasional, archived transfers more than daily work.

3. A data diode or a transfer kiosk

A data diode is hardware that lets data flow one way only, between two networks: certified, fast and built for machine-to-machine streams such as historian data. A transfer kiosk (in French, a station blanche) scans removable media before they enter or leave. Both are organisation projects: hardware, integration and budgets of thousands of euros. See Bouraq vs data diodes and kiosks.

4. A photo of the screen

It works for one error message. For anything longer it is lossy, unreadable by OCR when the text is code or a table, unencrypted on the phone, and leaves no record a security team can review.

5. Free QR code and optical tools

Open-source tools such as libcimbar stream files as animated codes that a phone decodes, much faster than Bouraq. They are excellent for a person moving their own files on their own machine. They give an organisation no account, no record, no approval and no way back. See Bouraq vs free QR tools.

6. Bouraq: encrypted QR codes into an account, with a record

Bouraq Prism, one HTML file opened on the offline PC, shows your files as QR codes encrypted with your account key. Your phone, or a webcam you are allowed to use, reads them into your space, where they are rebuilt and checked by sha256. Every transfer belongs to a named account and is time-stamped. Changes come back through your private GitHub or GitLab repository or a USB key.

It is slower than a USB key (about 5 kB/s), and it needs a camera allowed in front of the screen. It is built for the files people move every week: logs, results, configuration, code context, reports.

The six options side by side

	Volume	Record for security	Way back	Cost
USB key under policy	Large	With media control	Yes	Low
CD or DVD	Medium	Manual log	Another disc	Low
Data diode	Large, continuous	Usually	No, one way by design	Thousands of euros and a project
Transfer kiosk	Large	Yes	Yes, through the kiosk	Thousands of euros a year
Photo of the screen	One screen	None	None	Free
Free QR tool	Medium	None	None	Free
Bouraq	Kilobytes to a few MB	Named account, sha256, audit trail	Private repository or USB key	€79 to €99 a month

Volumes are orders of magnitude, not benchmarks. Diode and kiosk prices come from public catalogues; see the comparison.

When Bouraq is the right one

A good fit

You move small files often: logs, results, configs, reports, code context
USB is banned or tedious, and a camera is allowed at the workstation
Your security team wants a named, time-stamped record of what left
You need the way back too, through a private repository or a USB key

Not a fit

Hundreds of megabytes or datasets: use a sanctioned USB path or a diode
Rooms where every camera is banned, classified areas, DR or VS-NfD data
Any transfer your organisation has not authorised
Continuous machine-to-machine streams: that is a diode's job

Honest scope. Bouraq needs a camera you are allowed to point at the screen, carries kilobytes to a few megabytes comfortably, and is for content you are authorised to move. It is not for classified, DR or VS-NfD information. Security and architecture →

Questions

How do I transfer files from an air-gapped computer without a USB key?

Ask your security team which channel is authorised, then use it: write-once discs, a data diode or kiosk installed by your organisation, or an optical channel such as encrypted QR codes read by an allowed camera. Bouraq is the last kind: one HTML file on the offline PC, nothing installed.

Can you transfer files from an air-gapped computer without the network?

Yes. An optical channel needs no cable, radio or network on the offline PC: its screen shows codes and a camera outside reads them. That is how Bouraq works, one way out by design; the way back is a separate channel your policy must allow.

Is transferring files by QR code secure?

A QR code is only as private as its content. Plain QR codes can be read by anyone who photographs the screen. Bouraq encrypts every code with your account key (XSalsa20-Poly1305), checks the rebuilt file by sha256 and records the transfer against a named account. It does not offer end-to-end encryption today: our server decrypts to rebuild the file, as the security page explains.

How fast is QR code file transfer?

With Bouraq, about 5 kB/s of compressed data on a full-HD screen: 1 MB of source code in about 48 s, 5 MB of logs in about 2 min 23 s, 1 MB of photos in about 3 min 10 s, per loop. Free tools built for raw speed are faster.

Is an optical transfer safer than a USB key?

On the way out, nothing is plugged into the offline PC, so nothing can carry malware into it. The remaining risks are different: anyone who can see the screen sees codes (Bouraq's are encrypted), and a camera must be allowed in the room. Your security team weighs both.

Move your next file with a record your security team can read.

See the price and start Security page for approvers

14-day money-back guarantee · €79 a month billed yearly, or €99 monthly.