One of the most popular applications of quantum computers is to break the mathematical difficulty of cryptography. Enterprises such as IBM, Google, and others have announced that they are improving their computing capabilities. The improvement of quantum computing has led to worry in some quarters about the demise of the currently used cryptography. Particularly the security of the Bitcoin blockchain.
A lot has been says about how quantum computing is a threat to the asymmetric cryptography in use today. In asymmetric cryptography, a public-private key pair is generate in such a way that both keys have a relationship between them.
The private key is kept secret while the public is publicly available. The private key that produces the digital signature can be verified by anyone who has the corresponding public key. This helps to prove the integrity of transactions.
There is a quantum algorithm that can break the security of the most common algorithms of asymmetric cryptography.This means that anyone with a quantum computer with the right capabilities can derive a private key from its corresponding public key. This would enable the person to falsify any digital signature.
How Bitcoin Transactions Work
In order to understand the impact of quantum computers on Bitcoin let’s consider how bitcoin transactions work. Unlike the banking system where the bank has the responsibility to provide customers with a bank account; on the Bitcoin blockchain, the user is responsible for generating his address.
The users generate a random bitcoin address as well as a secret key that is require in order to perform transactions from this user address. Transactions on the Bitcoin blockchain are similar to sending money from one bank account to another. The sender must authorize the transaction by providing a digital signature that proves ownership of the address where the funds are store.
The Miners pick up the transaction and verify it. They compete in a race to process blocks of transactions which is call a block. Bitcoin blocks are then link to each other sequentially to form a chain of blocks known as the blockchain.
Is the Bitcoin blockchain resilient to attacks?
Assuming owners of vulnerable bitcoins transfer their funds to safe addresses, does this mean the bitcoin blockchain is no longer vulnerable to attacks? No, it doesn’t mean it is no longer vulnerable. The condition for security is that public keys associated with wallet addresses are no longer publicly available. However, the moment you want to transfer coins from a safe address, you also reveal the public key. This makes the address vulnerable.
Between the time you reveal the public key and the time your transaction is mine, an attacker with a computer of sufficient computing power has a window of opportunity to steal your coins. All he needs to do is to first derive your private key from the public key and then initiate a competing transaction to his own address. He then tries to get priority over the original transaction by offering a higher mining fee.
In the Bitcoin blockchain, it currently takes about 10 minutes for transactions to be mine unless the network is congested which has happened frequently in the past.
As long as it takes a quantum computer longer to derive the private key of a specific public key then the network should be safe against quantum attacks.
This means that Bitcoin should be, in principle, resistant to quantum attacks as long as you do not reuse addresses.However, as the field of quantum computers is still in its infancy, it is unclear how fast such a quantum computer will become in the future. If a quantum computer will ever get closer to the 10 minutes mark to derive a private key from its public key, then the Bitcoin blockchain will be inherently broken.