Protocol Overview

This section establishes a basic understanding of the Glacier protocol in order to facilitate its execution. For more background on the protocol’s design, see the Glacier design document.

As described previously, the Glacier protocol involves putting bitcoins in cold storage, using multisignature security, with the keys stored only on paper.

Eternally Quarantined Hardware

This bulk of the Glacier protocol consists of ways to safeguard against theft of private keys due to malware infection. To accomplish this, Glacier uses eternally quarantined hardware.

Quarantined hardware means we drastically limit the ways in which a piece of hardware interfaces with the outside world in order to prevent the transmission of sensitive data (e.g. private keys) or harmful data (e.g. malware). We consider all interfaces – network, USB, printer, and so on – because any of them might be used to transmit malware or private keys.

Eternally quarantined hardware means we use factory-new hardware for this purpose (to minimize risk of prior malware infection), and never lift the quarantine. The quarantine is permanent because any malware infection which does somehow get through the quarantine might wait indefinitely for an opportunity to use an available interface (e.g. the Internet, if a quarantined laptop is later used to access the web). Eternal quarantining renders the hardware essentially useless for anything else but executing this protocol.

Parallel Hardware Stacks

There is a class of attacks which rely not on stealing your sensitive data (e.g. private keys), but in subverting the process of generating your sensitive data so it can be more easily guessed by a third party. We call this “flawed data.”

For example, a variant of the Trojan.Bitclip attack which replaces keys displayed on your screen (or keys stored in your clipboard) with insecure keys.

Because we are generating our data in eternally quarantined environments, any malware infection attempting this is unlikely to have come from your other computers – it would likely have already been present when the quarantined system arrived from the manufacturer. For example, the Lenovo rootkit or this Dell firmware malware infection.

The way to defeat these attacks is to detect them before we actually use the flawed data. We can detect such an attack by replicating the entire data generation process on two sets of eternally quarantined hardware, from different manufacturers. If the process generates identical data on both sets of hardware, we can be highly confident the data is not flawed because it would have to be an identical attack present on both sets of hardware, factory-new from different manufacturers. This is exceptionally unlikely.

Bitcoin Core and GlacierScript

Glacier uses the Bitcoin Core software for all cryptographic and financial operations, as its open source code is the most trustworthy. This is due to its track record of securing large amounts of money for many years, and the high degree of code review scrutiny it has received.

Glacier also utilizes GlacierScript, a software program that automates much of the manual work involved in executing the protocol. GlacierScript’s open source code is straightforward and extensively commented to facilitate easy review for flaws or vulnerabilities.

Protocol Output

The end result of the Glacier protocol is a set of paper information packets, one for each private key needed for the multisignature withdrawal policy. Each packet includes the following information:

• One private key – an alphanumeric string used to secure the funds
• The cold storage address – an alphanumeric string designating the virtual “location” of the funds
• The “redemption script” – an additional code needed to access funds, shared by all private keys.

Technical details: The Glacier protocol reuses Bitcoin addresses. See the design document for a detailed analysis.

Protocol Cost

The Glacier protocol requires over $600 in equipment, and approximately 8 hours of work to perform an initial cold storage deposit. This excludes time for:

• Obtaining equipment
• Printing documents
• Downloading files
• Physically storing the resulting Bitcoin keys

Subsequent deposits and withdrawals re-use the same equipment and take a fraction of the time.

No Formal Support

As a free, volunteer-developed community project, there is no formal support channel for Glacier should you encounter any issues. However, you may be able to ask advice of community members on our Gitter chat room or other Bitcoin community forums.

Privacy Considerations

Because the Bitcoin blockchain is public, the way you route and store funds has privacy implications. For example, any person to whom you give your cold storage address (because, for example, they’re sending you funds which you want to keep in cold storage) can see your total cold storage balance. This is easy to do with many free services (e.g. Blockstream ).

This is true not just of individuals, but entities. That is, any online wallet service which you use to send funds to cold storage can see your cold storage balance, and may deduce that it belongs to you. They may, of course, also choose to share this information with others.

If this is a concern for you, the easiest way to keep your cold storage balance private from a particular entity is to route the payment through one (or more) intermediary addresses before sending it to your cold storage address, with a few transactions going to each intermediate address. This does not provide perfect privacy, but each intermediate address provides increasing levels of obfuscation and uncertainty.

If privacy is very important to you, you might consider using a service like Shapeshift to exchange your Bitcoins for an more anonymous cryptocurrency, such as Monero, and then exchange them back to Bitcoins. However, this will cost you fees, and importantly, it requires you trust the operator of the exchange service not to steal or lose your funds.

Lower-security Protocol Variants

If you are willing to accept lower security for lower cost, you can do so with only slight modifications:

1. Perform this protocol using only one quarantined computer. Glacier protocol repeats all operations on two computers to detect defects or tampering in the key generation process. However, this is costly and adds significantly to the labor required to execute the protocol. The risks it mitigates are small: that malware conducting flawed key-generation attacks found its way onto the eternally quarantined systems, or that the computer firmware was tampered with at the manufacturer to include such malware. If you are willing to accept this risk, you could skip buying the parallel hardware stack (and needing the second setup computer) and skip the process of re-generating and verifying keys & transactions on the parallel hardware stack.

2. Use existing hardware. An even lower-security variant is to use nothing but existing laptops you already possess, disabling all network connections during protocol execution, instead of purchasing new quarantined hardware. This fails to protect against some malware attacks, but provides additional savings in cost and effort.

Such as an existing infection of a laptop’s firmware, malware which overrides OS settings to disable wireless connectivity, or certain undiscovered vulnerabilities in the software used by the protocol.

These modifications are left as an exercise to the reader.

Out of scope

There’s always more one could do to increase security. While Glacier is designed to provide strong protection for almost everyone, some situations (e.g. being the focus of a targeted attack by a sophisticated, well-resourced criminal organization) are beyond its scope.

For some additional security precautions beyond those provided in the standard protocol, see the possible improvements to Glacier.