Are your bitcoins threatened by the quantum computer?

It is no longer so, but when. The quantum computer will soon be a reality and it is time to do the accounts. How many bitcoins are currently threatened?

Bitcoin and cryptography

The recent advances of Google and Microsoft in the field of quantum computers have changed consensus. Several BIPs are already on the table to address the threat.

Do not miss our previous article about BIP-360. You will find a plethora of information on the subject. Today’s article focuses on the exact BTC number currently vulnerable to quantum threat. The figures come from Chaincode Labs report Presented by Anthony Milton on the occasion of the Quantum Bitcoin Summit.

Before the numbers, let's make a quick recall of the cryptographic cogs of Bitcoin. Let's start from the Bitcoin addresses that are most familiar to us. These addresses are encodings of public keys, hence the expression “public key cryptography”, which are also called “asymmetrical cryptography”.

These public keys are created from a private key that is commonly called the “seed”. That is to say on the 12 or 24 words that generate the creation of a wallet. These 12 words actually represent a large number of 128 bits (plus a checksum) from which your Wallet can derive from billions of public keys (Bitcoin addresses).

Nowadays, the “public keys” are no longer really public. As said above, they are encoded while passing the Ripemd-160 quantum computer to the reel resistant and, above all, SHA-256. The resulting hash is called a “bitcoin address”.

These addresses are used to build UTXO (Unspent Transaction Output). This barbaric expression refers to the “scripts” (a piece of code) which lock a quantity of BTC (a figure) to a public key.

Each BTC transaction consumes and creates UTXO at the same time. There are currently around 170 million.

The Incassable SHA-256

Wallets therefore do not contain bitcoins strictly speaking, but private and public keys. These keys are very large numbers linked by a mathematical “one -way” mathematical function. In other words, it is impossible for a classic computer to calculate a private key from a public key.

Problem, quantum computers could get there (thanks to Shor algorithm). Sharp minds will say: “So what?” No problem since we have said that the addresses are encoded with the SHA-256 algorithm which is resistant to the quantum computer. ”

Quite. A public key hidden behind a SHA-256 encoding is safe, whatever happens. However, carrying out a transaction is required to reveal the public key associated with the UTXO that we spend.

After this transaction, the public key is known to all. It is therefore no longer necessary to reuse the address in question to receive new BTC. Unfortunately, it turns out that many addresses are reused.

To these reused addresses must be added the addresses of the very first types of UTXO which were simply the public keys, without any encoding. The name of this type of script is P2PK (Pay-2 Public-Key). And then finally the P2TR type UTXO (Pay-2-Taproot) spent.

In all, Chaincode calculated that 32.7 % of BTCs are currently vulnerable. About 6.36 million bitcoins. On this large total, 69 % (103 million UTXO representing 4.49 million BTC) are vulnerable due to the reuse of addresses.

The rest mainly consists of UTXO of P2PK type (1.87 million BTC), or 8.65 % of BTCs in circulation. And UTXO P2TR (0.15 million BTC).

Are your bitcoins in danger?

Yes, if you reused an address after using it to make a transaction.
Yes, if your addresses are of the P2PK type. However, there is little chance that this is the case if you installed your wallet after 2011.

Yes also if you have participated in the fashion of “ordinals” and other inscriptions which mainly use the UTXO P2TR. However, it is UTXO containing very little BTC.

The site of Project 11 Allows you to check if some of your addresses have been reused. If this is the case, you just have to send you these BTCs to yourself, on a new address.

Here is a list of the types of addresses resistant to the quantum computer (if you do not reuse them):

• P2PKH addresses (Pay-2-Public-Key-Hash). These addresses always start with ” 1 ». For example :

1HSK3S3O1NBVSB7RKAVWF7V9MVHT2HWZQ8 (34 characters)

• P2SH addresses (Pay-to-Script-Hash). They always start with ” 3 ». For example :

3dymavewh38huzhz3vwyaqr8ytztupmsna (34 characters)

• Addresses P2WPKH (Pay-to-Witness-Public-Key-Hash, Segwit) and P2WSH (Pay-to-Witness-Script-Hash, Segwit). They both start with ” BC1Q ». For example :

BC1QW508D6QEJXTDG4Y5R3ZARVARY0C5XW7KV8F3T4 (42 characters)
BC1QRP33G0Q5C5TXSP9ARYSRX4K6ZDKFS4CUN4XJ0GDCCCCEFVPSXF3QCFMV3 (62 characters)

Let's finish by noting that less than 20 % of the addresses have been reused. The problem being that they are linked to more than 60 % of UTXO and 22.5 % of bitcoins. In question, the exchange platforms which very often reuse the same addresses.

The reused address containing the most BTC belongs for example to Binance, with 249,000 BTC which could be sucked by a quantum computer …

Bitcoins linked to reused addresses can easily be moved to new addresses. But according to the estimates of Anthony Milton, around 2 million lost bitcoins will remain vulnerable, especially those of Satoshi Nakamoto.

In this regard, do not miss our article: Should we erase the bitcoins of Satoshi Nakamoto (before the advent of the quantum computer)?