Cryptographic functions like RIPEMD or SHA often use "nothing up my sleeve values" to provide security that a constant was not chosen to enable some cryptographic flaw or "backdoor" in the algorithm. For example SHA uses constants for the initial values of the block segments. Technically these could be any random number but that would lead to concern that the 'random' number isn't actually random.
Bitcoin address
So SHA uses first 32 bits of the fraction portion of the cube root of the first 8 prime numbers. This allows verification when a pseudo random number is needed. It is very unlikely there is some magical property between the fractional portion of the cube root of sequential prime numbers that undermines SHA Come up with an address that passes the basic sanity checks but is internally invalid. You can know for sure that no key could possibly match this address.
Put strings of characters in the address that are way beyond what anyone could generate in a vanity address. For example, if the Bitcoin address has "FourScoreAndSevenYearsAgo" in it, it's clearly beyond anyone's capability to find a corresponding private key. Use a public key that's obviously made up, such as one that consists only of zero bytes or that contains all consecutive digits of Pi. It's clearly beyond anyone's capability to find a corresponding private key. For this one to work, you need to disclose the public key.
Use a hash of the public key that's obviously made up. This works the same as the option above, but the difficulty would be in even finding a public key with such a hash, much less finding the corresponding private key. What is the catch? As normally you'd generate the public key from a private key and hash it a couple times, in order to retrieve coins from the address you generated, one would have to find such a specific number in point 1, that after points 2 and 3 would generate your bogus number. The more orderly the number you used in point 3 is, the more people would believe that it is an obviously fake address.
If you want to use an address, it would be nice to generate an address that can be verified by a human as obviously unspendable just by looking at the Base When you look at these addresses, you will say, "wow, that is obviously unspendable. These addresses are characterized by a human-readable identifier at the start, followed by a large number of X 's. In order to spend the funds from an address like this, you would need to first reverse the hash impossible , then find the private key that corresponds to the public key that you got also impossible.
Note that the last six digits of these addresses are Base58Check checksums. This is the only tricky part of the process: you need to search over about 4 billion strings until you find a valid Base58Check string. This will only take an instant, though. Inspired by this other StackExchange answer. The methods described by DeathAndTaxes are appropriate. However, I would like to present an alternative method where you can provably burn coins and also include sufficient information in the address.
We used this method in the first versions of OpenBazaar and it is called an "almost-collision coin burning". The mechanism employed to achieve that is simple: While a UTXO is maintained for all unspent regular transactions, when an OP-RETURN transaction is received by a full node, the full node can avoid adding that transaction to the UTXO completely, as the OP-RETURN script constitutes a proof that the amount remains unspendable and hence no future transaction can attach this dangling output to its input; it is hence a permanent dangling output edge.
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After the initial OP-RETURN operator, the rest of the script data can contain information about why the coin was burned, so that different applications can demand different burning, and so that the association with an account is possible. The fact that this code is non-executable follows from that it will never be executed due to the earlier exception. In particular, for simplicity of implementation and usage, as well as for separation of concern reasons, we decided that OpenBazaar does not need to include a bitcoin wallet implementation. Instead, the user can use any existing wallet software they wish.
Hence, to make payments required by OpenBazaar, either for product purchases or for burn transactions, the user would have to utilize their wallet directly. The only way to create burn transactions are through manual issuing of script commands by the user, which can be confusing or impossible to execute for an average user without a programming background.
While a wallet software could offer an API to do that, we are not aware of such implementations just yet. For these reasons, we designed an alternative mechanism for coin burning which uses simple standard pay-to-pubkey-hash transactions. These transactions are treated normally by the bitcoin full nodes, hence they are propagated as required. Furthermore, it is easy for regular wallets to create such transactions, and users can easily understand the process and make the payment without worrying that an unnecessary amount of money will be transferred and without requiring special programming knowledge.
Our schema for burning is based on the following cryptographic assumption, a resistance to an almost-collision: It is computationally infeasible to calculate two hash pre-image values x1, x2 such that:. This assumption is strongly supported by the fact that a hash function is cryptographically secure; if this equation did not hold, a collision would have been found, modulo one bit, which indicates the hash is broken up to almost all of its bits.
Regular bitcoin addresses are generated from regular bitcoin ECDSA keys as shown in the standard bitcoin address generation algorithm. To generate an address that is provably unspendable, the burner starts with their ECDSA OpenBazaar public key and applies the same process. Specifically, they flip the last bit of the hash output. The rest of the process follows identically. Finally, the burner transfers the amount of coin they wish to burn to this generated address.
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I will now illustrate the properties of correctness, uniqueness, and security for this scheme. To verify the correctness of the burn, a third party performs the same transformation as the burner. They begin from the public ECDSA key of the OpenBazaar node whose trust they wish to verify and follow the bitcoin address generation process, applying the same perturbation as the burner after the SHA stage.
Arriving at the final bitcoin address, the verifier then checks the blockchain for money that was sent to this address. This concludes that the burn an honest burner performs will be correctly verified by an honest verifier. This is a significant advantage when compared to alternative schemes that do not contain why-burned information such as nothing-up-my-sleeve addresses. Under the assumption that RIPEMD is hard to reverse and the fact that SHA is a cryptographically secure hash function, assumptions already made by bitcoin, the uniqueness of burn address for each OpenBazaar key follows directly.
For this scheme to be secure, we must prove that the burned money cannot actually be spent by anyone. Indeed, if the money were spendable, the spender would have to know the private key associated with a public key which hashes to the perturbed SHA value. However, this would allow the generation of an almost-collision in RIPEMD, as the public key that can be used for spending the burned money and the public key of the OpenBazaar identity would constitute pre-images of hashes that only differ by one bit. From the almost-collision resistance assumption, we conclude that this is computationally infeasible.
The almost-collision method of coin burning introduces scalability challenges for the bitcoin software. Networked The networked wallet receives the signed transaction from the hardware wallet and broadcasts it to the network. The primary advantage of hardware wallets is their possibility for greatly improved security over full-service wallets with much less hassle than offline wallets.
The primary disadvantage of hardware wallets is their hassle. Even though the hassle is less than that of offline wallets, the user must still purchase a hardware wallet device and carry it with them whenever they need to make a transaction using the signing-only wallet.
Creating Bitcoin Private Keys with Dice
An additional hopefully temporary disadvantage is that, as of this writing, very few popular wallet programs support hardware wallets—although almost all popular wallet programs have announced their intention to support at least one model of hardware wallet. Wallet programs which run in difficult-to-secure environments, such as webservers, can be designed to distribute public keys including P2PKH or P2SH addresses and nothing more.
There are two common ways to design these minimalist wallets:. Pre-populate a database with a number of public keys or addresses, and then distribute on request a pubkey script or address using one of the database entries.
Start with an invalid public key
To avoid key reuse , webservers should keep track of used keys and never run out of public keys. This can be made easier by using parent public keys as suggested in the next method. Use a parent public key to create child public keys. This can be a database entry for each key distributed or an incrementing pointer to the key index number. Neither method adds a significant amount of overhead, especially if a database is used anyway to associate each incoming payment with a separate public key for payment tracking.
See the Payment Processing section for details. Bitcoin wallets at their core are a collection of private keys. These collections are stored digitally in a file, or can even be physically stored on pieces of paper. Private keys are what are used to unlock satoshis from a particular address. In Bitcoin, a private key in standard format is simply a bit number, between the values:.
In order to make copying of private keys less prone to error, Wallet Import Format may be utilized. WIF uses base58Check encoding on a private key, greatly decreasing the chance of copying error, much like standard Bitcoin addresses.
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