Bitcoin quantum protection: why transaction signatures need to change<\/h2>\r\n\r\n\r\n\r\n![\"Bitcoin](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic2-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\nA private key is the secret number a wallet uses to sign transactions, so anyone who knows it can spend the coins. The public key is calculated from it and lets the network verify the signature. Knowing the public key does not let someone spend your funds using an ordinary computer, but a sufficiently powerful quantum computer could use it to recover the private key. Your wallet handles the routine calculations automatically, so you do not need to work with the keys yourself.<\/p>\r\n\r\n\r\n\r\n
Calculating a public key from a private key is straightforward, but recovering the private key from the public key is practically impossible on a modern conventional computer<\/strong>. Trying the enormous number of possible keys one by one would take far too long to be a practical attack.<\/p>\r\n\r\n\r\n\r\nBitcoin and ordinary Ethereum accounts use the same mathematical foundation for their signatures, but expose public keys under different conditions. Understanding the quantum threat therefore means looking at the address type and its past transactions, as well as the network.<\/p>\r\n\r\n\r\n\r\n
How Shor’s algorithm could recover a private key<\/h2>\r\n\r\n\r\n\r\n![\"Shor's](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic3-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\nIn 1994, mathematician Peter Shor proposed a quantum algorithm that can calculate a private key from a public key without trying every possible value. An attacker would need a sufficiently powerful and reliable quantum computer to use it.<\/p>\r\n\r\n\r\n\r\n
Qubits are the units of information a quantum computer works with. Physical qubits are the actual hardware elements, which are prone to errors. To make long calculations more reliable, many physical qubits are combined into a logical qubit, with errors corrected within the group.<\/p>\r\n\r\n\r\n\r\n
A thousand physical qubits are not the same as a thousand logical qubits<\/strong>: one logical qubit may require hundreds of physical qubits or more. A processor’s advertised qubit count alone therefore does not tell you whether it could recover a Bitcoin private key.<\/p>\r\n\r\n\r\n\r\nWhat quantum hardware would an attacker need?<\/h2>\r\n\r\n\r\n\r\n
On March 30, 2026, Google Quantum AI, together with researchers from the Ethereum Foundation and Stanford, published a study of quantum vulnerabilities in cryptocurrencies<\/a>. The authors revised estimates of how many qubits and how much time would be needed to recover a Bitcoin private key from its public key.<\/p>\r\n\r\n\r\n\r\nThe researchers considered two approaches to the calculation:<\/p>\r\n\r\n\r\n\r\n
\r\n- Fewer than 1,200 logical qubits<\/strong>, requiring fewer qubits but more computing operations.<\/li>\r\n\r\n\r\n\r\n
- Fewer than 1,450 logical qubits<\/strong>, using more qubits to reduce the number of computing operations.<\/li>\r\n<\/ul>\r\n\r\n\r\n\r\n
The authors estimate that either approach would need fewer than 500,000 physical qubits<\/strong>, provided the hardware achieves the required speed and reliability. That is roughly twenty times fewer than earlier estimates. The result depends on the hardware’s capabilities and how effectively the system corrects errors during the calculation.<\/p>\r\n\r\n\r\n\r\nThe full calculation would take about 18\u201323 minutes. Some of the work could be done in advance, before obtaining the victim’s public key. If that preparation were preserved on the quantum computer, about 9 or 12 minutes of computation would remain after obtaining the key, depending on the approach.<\/p>\r\n\r\n\r\n\r\n
An attacker could try to steal the coins while your transfer is waiting for confirmation. Sending funds from an address that hid the public key makes that key visible in the transaction. Before being included in a block, the transaction waits in the mempool, the pool of unconfirmed transactions. A fast enough quantum computer could calculate the private key during that wait, allowing the attacker to send the same coins to themselves and offer the miner a higher fee.<\/p>\r\n\r\n\r\n\r\n
Assuming the calculation takes nine minutes and Bitcoin blocks arrive every ten minutes on average, the authors estimated a roughly 41% chance of stealing the coins before the transfer is confirmed<\/strong>. This assumes the attacker obtains the public key immediately, the network is not congested and their transaction can be included in a block instead of yours. In the same model, the chance is below 3% for Litecoin and less than one in eight thousand for Dogecoin. These are possible future attacks that would require the necessary hardware.<\/p>\r\n\r\n\r\n[vc_message color=”warning” message_box_style=”classic” message_box_color=”alert-warning” style=”rounded”]<\/p>\r\n
Google calculated the requirements for future hardware; it did not recover a Bitcoin private key on an existing quantum computer. The researchers also provided a mathematical proof that allows their estimates to be checked without publishing full instructions for the attack.<\/p>\r\n
[\/vc_message]<\/p>\r\n\r\n\r\n
When the public key becomes visible on the blockchain<\/h2>\r\n\r\n\r\n\r\n![\"Public](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic4-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\nAn attack using Shor’s algorithm requires the public key. A Bitcoin address and a public key are different things<\/strong>: some address formats expose the key immediately, while others initially show only its digital fingerprint. Other formats hide the spending rules behind a fingerprint, such as a requirement for multiple signatures.<\/p>\r\n\r\n\r\n\r\nFor P2PKH and P2WPKH addresses, the public key is initially hidden behind a hash and becomes visible when you send coins from the address. Shor’s algorithm needs the public key itself, so its fingerprint alone is not enough for this attack. After a transfer, that advantage is lost: if coins remain at the same address or you receive more funds there, an attacker can already see the public key they would need.<\/p>\r\n\r\n\r\n\r\n
<\/figure>\r\n<\/div>\r\n\r\n\r\nA private key is the secret number a wallet uses to sign transactions, so anyone who knows it can spend the coins. The public key is calculated from it and lets the network verify the signature. Knowing the public key does not let someone spend your funds using an ordinary computer, but a sufficiently powerful quantum computer could use it to recover the private key. Your wallet handles the routine calculations automatically, so you do not need to work with the keys yourself.<\/p>\r\n\r\n\r\n\r\n
Calculating a public key from a private key is straightforward, but recovering the private key from the public key is practically impossible on a modern conventional computer<\/strong>. Trying the enormous number of possible keys one by one would take far too long to be a practical attack.<\/p>\r\n\r\n\r\n\r\n Bitcoin and ordinary Ethereum accounts use the same mathematical foundation for their signatures, but expose public keys under different conditions. Understanding the quantum threat therefore means looking at the address type and its past transactions, as well as the network.<\/p>\r\n\r\n\r\n\r\n In 1994, mathematician Peter Shor proposed a quantum algorithm that can calculate a private key from a public key without trying every possible value. An attacker would need a sufficiently powerful and reliable quantum computer to use it.<\/p>\r\n\r\n\r\n\r\n Qubits are the units of information a quantum computer works with. Physical qubits are the actual hardware elements, which are prone to errors. To make long calculations more reliable, many physical qubits are combined into a logical qubit, with errors corrected within the group.<\/p>\r\n\r\n\r\n\r\n A thousand physical qubits are not the same as a thousand logical qubits<\/strong>: one logical qubit may require hundreds of physical qubits or more. A processor’s advertised qubit count alone therefore does not tell you whether it could recover a Bitcoin private key.<\/p>\r\n\r\n\r\n\r\n On March 30, 2026, Google Quantum AI, together with researchers from the Ethereum Foundation and Stanford, published a study of quantum vulnerabilities in cryptocurrencies<\/a>. The authors revised estimates of how many qubits and how much time would be needed to recover a Bitcoin private key from its public key.<\/p>\r\n\r\n\r\n\r\n The researchers considered two approaches to the calculation:<\/p>\r\n\r\n\r\n\r\n The authors estimate that either approach would need fewer than 500,000 physical qubits<\/strong>, provided the hardware achieves the required speed and reliability. That is roughly twenty times fewer than earlier estimates. The result depends on the hardware’s capabilities and how effectively the system corrects errors during the calculation.<\/p>\r\n\r\n\r\n\r\n The full calculation would take about 18\u201323 minutes. Some of the work could be done in advance, before obtaining the victim’s public key. If that preparation were preserved on the quantum computer, about 9 or 12 minutes of computation would remain after obtaining the key, depending on the approach.<\/p>\r\n\r\n\r\n\r\n An attacker could try to steal the coins while your transfer is waiting for confirmation. Sending funds from an address that hid the public key makes that key visible in the transaction. Before being included in a block, the transaction waits in the mempool, the pool of unconfirmed transactions. A fast enough quantum computer could calculate the private key during that wait, allowing the attacker to send the same coins to themselves and offer the miner a higher fee.<\/p>\r\n\r\n\r\n\r\n Assuming the calculation takes nine minutes and Bitcoin blocks arrive every ten minutes on average, the authors estimated a roughly 41% chance of stealing the coins before the transfer is confirmed<\/strong>. This assumes the attacker obtains the public key immediately, the network is not congested and their transaction can be included in a block instead of yours. In the same model, the chance is below 3% for Litecoin and less than one in eight thousand for Dogecoin. These are possible future attacks that would require the necessary hardware.<\/p>\r\n\r\n\r\n [vc_message color=”warning” message_box_style=”classic” message_box_color=”alert-warning” style=”rounded”]<\/p>\r\n Google calculated the requirements for future hardware; it did not recover a Bitcoin private key on an existing quantum computer. The researchers also provided a mathematical proof that allows their estimates to be checked without publishing full instructions for the attack.<\/p>\r\n [\/vc_message]<\/p>\r\n\r\n\r\n An attack using Shor’s algorithm requires the public key. A Bitcoin address and a public key are different things<\/strong>: some address formats expose the key immediately, while others initially show only its digital fingerprint. Other formats hide the spending rules behind a fingerprint, such as a requirement for multiple signatures.<\/p>\r\n\r\n\r\n\r\n For P2PKH and P2WPKH addresses, the public key is initially hidden behind a hash and becomes visible when you send coins from the address. Shor’s algorithm needs the public key itself, so its fingerprint alone is not enough for this attack. After a transfer, that advantage is lost: if coins remain at the same address or you receive more funds there, an attacker can already see the public key they would need.<\/p>\r\n\r\n\r\n\r\nHow Shor’s algorithm could recover a private key<\/h2>\r\n\r\n\r\n
<\/figure>\r\n<\/div>\r\n\r\n\r\nWhat quantum hardware would an attacker need?<\/h2>\r\n\r\n\r\n\r\n
\r\n
When the public key becomes visible on the blockchain<\/h2>\r\n\r\n\r\n
<\/figure>\r\n<\/div>\r\n\r\n\r\n
![\"A](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic5-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\n![\"Checking](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic6-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\n![\"Google](\"https:\/\/lwallet.com.ua\/wp-content\/uploads\/2026\/10\/blog-quantum-computers-protection-07-10-2026-content-pic7-1024x573.jpg\" "\\"\\"")
<\/figure>\r\n<\/div>\r\n\r\n\r\n