How Are Bitcoin Public Keys Generated
Your bitcoin private key is a randomly generated string (numbers and letters), allowing bitcoins to be spent. A private key is always mathematically related to the bitcoin wallet address, but is impossible to reverse engineer thanks to a strong encryption code base. A Bitcoin wallet is as simple as a single pairing of a Bitcoin address with its corresponding Bitcoin private key. Such a wallet has been generated for you in your web browser and is displayed above. To safeguard this wallet you must print or otherwise record the Bitcoin address and private key. It is important to make a backup copy of the private key and store it in a safe location. Mar 28, 2019 An address is derived from the public key through the use of a one-way cryptographic hash function. With Bitcoin, the algorithms that are used to make a bitcoin address from the public key are the Secure Hash Algorithm 256 and the RACE Integrity Primitives Evaluation Message Digest 160. Beginning with the public key, this string of values is first ran through the SHA-256 hashing algorithm. Feb 12, 2015 As seen in our guides to elliptic curve cryptography and how to create a Bitcoin Private key – a public key is in fact just coordinates on the Bitcoin curve calculated through multiplying the generator point by the private key number. X coordinate= 7a633d546e723c3f2f2a227b6d393b35303d38.
Mar 27, 2018 A new keypair is generated for each receiving address (with newer HD wallets, this is done deterministically).The public key and their associated private keys (or the seed needed to generate them) are stored in the wallet data file.This is the only file users should need to backup.A 'send' transaction to a specific Bitcoin address requires.
This article may be too technical for some users. The more basic article on Bitcoin Addresses may be more appropriate.
A Bitcoin address is a 160-bit hash of the public portion of a public/private ECDSA keypair. Using public-key cryptography, you can 'sign' data with your private key and anyone who knows your public key can verify that the signature is valid.
A new keypair is generated for each receiving address (with newer HD wallets, this is done deterministically).The public key and their associated private keys (or the seed needed to generate them) are stored in the wallet data file.This is the only file users should need to backup.A 'send' transaction to a specific Bitcoin address requires that the corresponding wallet knows the private key implementing it.This has the implication that if you create an address and receive coins to that address, then restore the wallet from an earlier backup, before the address was generated, then the coins received with that address are lost; this is not an issue for HD wallets where all addresses are generated from a single seed.Addresses are added to an address key pool prior to being used for receiving coins. If you lose your wallet entirely, all of your coins are lost and can never be recovered.
Bitcoin allows you to create as many addresses as you want, and use a new one for every transaction.There is no 'master address': the 'Your Bitcoin address' area in some wallet UIs has no special importance.It's only there for your convenience, and it should change automatically when used.
Bitcoin addresses contain a built-in check code, so it's generally not possible to send Bitcoins to a mistyped address. However, if the address is well-formed but no one owns it (or the owner lost their wallet.dat), any coins sent to that address will be lost forever.
Hash values and the checksum data are converted to an alpha-numeric representation using a custom scheme: the Base58Check encoding scheme. Under Base58Check, addresses can contain all alphanumeric characters except 0, O, I, and l. Normal addresses currently always start with 1 (addresses from script hashes use 3), though this might change in a future version. Testnet addresses usually start with m or n. Mainline addresses can be 25-34 characters in length, and testnet addresses can be 26-34 characters in length. Most addresses are 33 or 34 characters long.
Collisions (lack thereof)
Since Bitcoin addresses are basically random numbers, it is possible, although extremely unlikely, for two people to independently generate the same address. This is called a collision. If this happens, then both the original owner of the address and the colliding owner could spend money sent to that address. It would not be possible for the colliding person to spend the original owner's entire wallet (or vice versa).
But because the space of possible addresses is so astronomically large it is more likely that the Earth is destroyed in the next 5 seconds, than that a collision occur in the next millenium.
How to create Bitcoin Address
The correct way to create a Bitcoin address is to use well tested, open source, peer reviewed wallet software. Manually handling keys has resulted in funds loss over and over again. Unlike other centralized systems losses in Bitcoin are usually unrecoverable.
Here is a brief overview of how address generation works, for informational purposes:
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0 - Having a private ECDSA key
1 - Take the corresponding public key generated with it (33 bytes, 1 byte 0x02 (y-coord is even), and 32 bytes corresponding to X coordinate)
2 - Perform SHA-256 hashing on the public key
3 - Perform RIPEMD-160 hashing on the result of SHA-256
4 - Add version byte in front of RIPEMD-160 hash (0x00 for Main Network)
(note that below steps are the Base58Check encoding, which has multiple library options available implementing it)
5 - Perform SHA-256 hash on the extended RIPEMD-160 result
6 - Perform SHA-256 hash on the result of the previous SHA-256 hash
7 - Take the first 4 bytes of the second SHA-256 hash. This is the address checksum
8 - Add the 4 checksum bytes from stage 7 at the end of extended RIPEMD-160 hash from stage 4. This is the 25-byte binary Bitcoin Address.
9 - Convert the result from a byte string into a base58 string using Base58Check encoding. This is the most commonly used Bitcoin Address format
See Also
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This page contains sample addresses and/or private keys. Do not send bitcoins to or import any sample keys; you will lose your money.
A private key in the context of Bitcoin is a secret number that allows bitcoins to be spent.Every Bitcoin wallet contains one or more private keys, which are saved in the wallet file.The private keys are mathematically related to all Bitcoin addresses generated for the wallet.
Because the private key is the 'ticket' that allows someone to spend bitcoins, it is important that these are kept secret and safe.Private keys can be kept on computer files, but are also often written on paper.
Private keys themselves are almost never handled by the user, instead the user will typically be given a seed phrase that encodes the same information as private keys.
Some wallets allow private keys to be imported without generating any transactions while other wallets or services require that the private key be swept.When a private key is swept, a transaction is broadcast that sends the balance controlled by the private key to a new address in the wallet.Just as with any other transaction, there is risk of swept transactions to be double-spending.
In contrast, bitcoind provides a facility to import a private key without creating a sweep transaction.This is considered very dangerous, and not intended to be used even by power users or experts except in very specific cases. Importing keys could lead to the Bitcoins being stolen at any time, from a wallet which has imported an untrusted or otherwise insecure private key - this can include private keys generated offline and never seen by someone else[1][2].
An example private key
In Bitcoin, a private key is a 256-bit number, which can be represented one of several ways.Here is a private key in hexadecimal - 256 bits in hexadecimal is 32 bytes, or 64 characters in the range 0-9 or A-F.
Range of valid ECDSA private keys
Nearly every 256-bit number is a valid ECDSA private key. Specifically, any 256-bit number from 0x1 to 0xFFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFE BAAE DCE6 AF48 A03B BFD2 5E8C D036 4140 is a valid private key.
The range of valid private keys is governed by the secp256k1 ECDSA standard used by Bitcoin.
Hierarchical Deterministic (HD) Wallet Keys
- Main article: Hierarchical deterministic wallet
Wallet software may use a BIP 32 seed to generate many private keys and corresponding public keys from a single secret value. This is called a hierarchical deterministic wallet, or HD wallet for short. The seed value, or master extended key, consists of a 256-bit private key and a 256-bit chain code, for 512 bits in total. The seed value should not be confused with the private keys used directly to sign Bitcoin transactions.
(Optional) Enter a key passphrase in the 2 empty fields for the added security before continuing. Error generating a key for authentication pass phrases. Keep moving your mouse over the blank area in any manner to help generate randomness for a few moments until the progress is complete.With the keys finished, PuTTY will show the relative information about the pair along with the public key for easier copying.4.
Users are strongly advised to use HD wallets, for safety reasons: An HD wallet only needs to be backed up once typically using a seed phrase; thereafter in the future, that single backup can always deterministically regenerate the same private keys. Therefore, it can safely recover all addresses, and all funds sent to those addresses. Non-HD wallets generate a new randomly-selected private key for each new address; therefore, if the wallet file is lost or damaged, the user will irretrievably lose all funds received to addresses generated after the most recent backup.
Base58 Wallet Import format
- Main article: Wallet import format
When importing or sweeping ECDSA private keys, a shorter format known as wallet import format is often used, which offers a few advantages.The wallet import format is shorter, and includes built-in error checking codes so that typos can be automatically detected and/or corrected (which is impossible in hex format) and type bits indicating how it is intended to be used.Wallet import format is the most common way to represent private keys in Bitcoin.For private keys associated with uncompressed public keys, they are 51 characters and always start with the number 5 on mainnet (9 on testnet). Private keys associated with compressed public keys are 52 characters and start with a capital L or K on mainnet (c on testnet). This is the same private key in (mainnet) wallet import format:
When a WIF private key is imported, it always corresponds to exactly one Bitcoin address.Any utility which performs the conversion can display the matching Bitcoin address.The mathematical conversion is somewhat complex and best left to a computer, but it's notable that the WIF guarantees it will always correspond to the same address no matter which program is used to convert it.
The Bitcoin address implemented using the sample above is: 1CC3X2gu58d6wXUW_SAMPLE_ADDRESS_DO_NOT_SEND_MffpuzN9JAfTUWu4Kj
Mini private key format
- Main article: Mini private key format
Some applications use the mini private key format. Not every private key or Bitcoin address has a corresponding mini private key - they have to be generated a certain way in order to ensure a mini private key exists for an address. The mini private key is used for applications where space is critical, such as in QR codes and in physical bitcoins. The above example has a mini key, which is:
Summary
Any Bitcoins sent to the address 1CC3X2gu58d6wXUW_SAMPLE_ADDRESS_DO_NOT_SEND_MffpuzN9JAfTUWu4Kj can be spent by anybody who knows the private key implementing it in any of the three formats, regardless of when the bitcoins were sent, unless the wallet receiving them has since made use of the coins generated.The private key is only needed to spend the bitcoins, not necessarily to see the value of them.
If a private key controlling unspent bitcoins is compromised or stolen, the value can only be protected if it is immediately spent to a different output which is secure.Because bitcoins can only be spent once, when they are spent using a private key, the private key becomes worthless.It is often possible, but inadvisable and insecure, to use the address implemented by the private key again, in which case the same private key would be reused.
See Also
References
Bitcoin Master Public Key
- ↑Bitcoin StackExchange - Why doc says importing private keys is so dangerous?
- ↑Bitcoin StackExchange - Why so many warnings about importing private keys?