How do I securely transfer information between airgapped systems?

Question

I'm trying to take information that's on Computer A, write it onto some form of persistent storage, and copy that information onto Computer B. Both will be running a relatively recent version of Windows 10. The computers may be hundreds of feet to tens of miles from each other.

My current plan to accomplish this is using USB flash drives. My threat model does not involve state level actors, merely people knowledgeable enough to use USB malware.

I'd like to know:

1. Alternatives to USB, for example if we have a serial port available
2. Where to find the state of the art as far as group policy for disabling any kind of execution of code that comes in over USB
3. Antivirus or otherwise that similarly protects the computer from USB based malware

The systems must be airgapped, and they must have this information transfer occur. The information is on the order of tens of MB, and will only be transferred about once every 24 hours. The device used for the transfer may be destroyed after a single use if that improves the security. We're not concerned so much about the integrity of the data (it's already encrypted + ECC formatted), more the possibility for Computer A to be infected with malware from the USB while it writes the data out.

Answer 1

I don't know the classification/confidentially level of the data that needs to be moved from Computer A to Computer B. You did state that these systems must be air gapped, so I will assume that the information is critical thus it needs to be protected.

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Option 1:

Save the required information to an Iron Key. Mail the Iron Key to Computer B location for data transfer. Iron Keys are not perfect, but they do use AES 256-bit hardware encryption, have password protection and use onboard anti-virus scanning and active malware defenses.

Pros:

This solution is more secure than a stand USB drive. The odds of getting infected by malware are low.

Cons:

Requires multiple Iron Keys, which cost about $130 a piece. Requires mailing costs and potential delays in deliver

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Option 2:

Save the required information to a flash memory card in an encrypted format. Mail the memory card to Computer B location for data transfer. Destroy the flash memory card.

Pros:

Flash memory cards are very cheap, so you can use a card once. The odds of getting infected by malware are low.

Cons:

Requires multiple cards. 30 cards cost about as much as a single Iron Key Requires mailing costs and potential delays in deliver

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Option 3:

Save the required information to an [Iron Key.] Use a non-air gapped system to securely transfer the files to a non-air gapped system at Computer B location. Save the files to another Iron Key. Upload the files to Computer B and erase the files from the Iron Key.

Pros:

Fastest method to move files between Computer A and Computer B.

Cons:

Requires 2 Iron Keys at both location Requires a secure non-air gapped system at both location. This system could a MacBook, which is stored in a safe until needed. It could also be iPad pro, which could be used to transfer the files. Overall this method is the most expensive, but it is the fastest and can be highly secure depending on the security controls established.