A Bitcoin address, or simply address, is an identifier of 27-34 alphanumeric characters, beginning with the number 1, 3 or bc1, that represents a possible destination for a bitcoin payment. Addresses can be generated at no cost by any user of Bitcoin. It is also possible to get a Bitcoin address using an account at an exchange or online wallet service. Also you can generate it offline and store on paper or at any digital storage.
There are currently three address formats in use in Bitcoin mainnet:
- P2PKH (Pay 2 Public Key Hash) which begin with the number 1
- P2SH (Pay 2 Script Hash) type starting with the number 3.
- Bech32 type starting with bc1.
It is also possible to get a Bitcoin address using an account at an exchange or online wallet service. Also you can generate it offline and store on paper or at any digital storage. There are currently three address formats in use in Bitcoin mainnet: P2PKH (Pay 2 Public Key Hash) which begin with the number 1. Mar 31, 2018 Bitcoin & Cryptology Let’s explore some more about the Seed and the pairing of Private Keys, Public Keys and Bitcoin Addresses. Our Electrum Wallet was generated using some random words called the Seed. But what exactly is this Seed, and what does it do? At the heart of Bitcoin is advanced Cryptology software that is used.
Full list of Bitcoin address prefixes
Example use | Leading symbol(s) | Example |
---|---|---|
Pubkey hash (P2PKH address) | 1 | 17VZNX1SN5NtKa8UQFxwQbFeFc3iqRYhem |
Script hash (P2SH address) However, the Spyhunter patch gets the newest technologies to detect such kind of dangerous applications. It is a real-time malware blocker intention to reduce malware and other potentially unwanted applications from installing or implementing. Vocaloid 5 activation key generator. Rootkits are usually hidden on your computer hard disk and encrypt folder and files to prevent detection by anti-virus applications. SpyHunter 5’s innovative blockers are offered as FREE-of-charge capabilities.Spyhunter 5 Serial Key detects and eliminates rootkits, which are made to collect your private data and ruined the hard drive information. SegWit Pay 2 Witness Public Key Hash (P2SH-P2WPKH) | 3 | 3EktnHQD7RiAE6uzMj2ZifT9YgRrkSgzQX |
SegWit mainnet (P2WPKH address) | bc1 | bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4 |
SegWit Testnet (P2WPKH address) | tb1 | tb1qw508d6qejxtdg4y5r3zarvary0c5xw7kxpjzsx |
SegWit mainnet (P2WSH address) | bc1 | bc1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3qccfmv3 |
SegWit Testnet (P2WSH address) | tb1 | tb1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3q0sl5k7 |
Private key (WIF, uncompressed pubkey) | 5 | 5Hwgr3u458GLafKBgxtssHSPqJnYoGrSzgQsPwLFhLNYskDPyyA |
Private key (WIF, compressed pubkey) | K or L | L1aW4aubDFB7yfras2S1mN3bqg9nwySY8nkoLmJebSLD5BWv3ENZ |
BIP32 pubkey | xpub | xpub661MyMwAqRbcEYS8w7XLSVeEsBXy79zSzH1J8vCdxAZningWLdN3 zgtU6LBpB85b3D2yc8sfvZU521AAwdZafEz7mnzBBsz4wKY5e4cp9LB |
BIP32 private key | xprv | xprv9s21ZrQH143K24Mfq5zL5MhWK9hUhhGbd45hLXo2Pq2oqzMMo63o StZzF93Y5wvzdUayhgkkFoicQZcP3y52uPPxFnfoLZB21Teqt1VvEHx |
Testnet pubkey hash | m or n | mipcBbFg9gMiCh81Kj8tqqdgoZub1ZJRfn |
Testnet script hash | 2 | 2MzQwSSnBHWHqSAqtTVQ6v47XtaisrJa1Vc |
Testnet Private key (WIF, uncompressed pubkey) | 9 | 92Pg46rUhgTT7romnV7iGW6W1gbGdeezqdbJCzShkCsYNzyyNcc |
Testnet Private key (WIF, compressed pubkey) | c | cNJFgo1driFnPcBdBX8BrJrpxchBWXwXCvNH5SoSkdcF6JXXwHMm |
Testnet BIP32 pubkey | tpub | tpubD6NzVbkrYhZ4WLczPJWReQycCJdd6YVWXubbVUFnJ5KgU5MDQrD9 98ZJLNGbhd2pq7ZtDiPYTfJ7iBenLVQpYgSQqPjUsQeJXH8VQ8xA67D |
Testnet BIP32 private key | tprv | tprv8ZgxMBicQKsPcsbCVeqqF1KVdH7gwDJbxbzpCxDUsoXHdb6SnTPY xdwSAKDC6KKJzv7khnNWRAJQsRA8BBQyiSfYnRt6zuu4vZQGKjeW4YF |
In cryptocurrencies, a private key allows a user to gain access to their wallet. The person who holds the private key fully controls the coins in that wallet. For this reason, you should keep it secret. And if you really want to generate the key yourself, it makes sense to generate it in a secure way.
Here, I will provide an introduction to private keys and show you how you can generate your own key using various cryptographic functions. I will provide a description of the algorithm and the code in Python.
Do I need to generate a private key?
Most of the time you don’t. For example, if you use a web wallet like Coinbase or Blockchain.info, they create and manage the private key for you. It’s the same for exchanges.
Mobile and desktop wallets usually also generate a private key for you, although they might have the option to create a wallet from your own private key.
So why generate it anyway? Here are the reasons that I have:
- You want to make sure that no one knows the key
- You just want to learn more about cryptography and random number generation (RNG)
What exactly is a private key?
Formally, a private key for Bitcoin (and many other cryptocurrencies) is a series of 32 bytes. Now, there are many ways to record these bytes. It can be a string of 256 ones and zeros (32 * 8 = 256) or 100 dice rolls. It can be a binary string, Base64 string, a WIF key, mnemonic phrase, or finally, a hex string. For our purposes, we will use a 64 character long hex string.
Why exactly 32 bytes? Great question! You see, to create a public key from a private one, Bitcoin uses the ECDSA, or Elliptic Curve Digital Signature Algorithm. More specifically, it uses one particular curve called secp256k1.
Now, this curve has an order of 256 bits, takes 256 bits as input, and outputs 256-bit integers. And 256 bits is exactly 32 bytes. So, to put it another way, we need 32 bytes of data to feed to this curve algorithm.
There is an additional requirement for the private key. Because we use ECDSA, the key should be positive and should be less than the order of the curve. The order of secp256k1 is
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
, which is pretty big: almost any 32-byte number will be smaller than it.Naive method
So, how do we generate a 32-byte integer? The first thing that comes to mind is to just use an RNG library in your language of choice. Python even provides a cute way of generating just enough bits:
Looks good, but actually, it’s not. You see, normal RNG libraries are not intended for cryptography, as they are not very secure. They generate numbers based on a seed, and by default, the seed is the current time. That way, if you know approximately when I generated the bits above, all you need to do is brute-force a few variants.
When you generate a private key, you want to be extremely secure. Remember, if anyone learns the private key, they can easily steal all the coins from the corresponding wallet, and you have no chance of ever getting them back.
So let’s try to do it more securely.
Cryptographically strong RNG
Along with a standard RNG method, programming languages usually provide a RNG specifically designed for cryptographic operations. This method is usually much more secure, because it draws entropy straight from the operating system. The result of such RNG is much harder to reproduce. You can’t do it by knowing the time of generation or having the seed, because there is no seed. Well, at least the user doesn’t enter a seed — rather, it’s created by the program.
Key Generator Download
In Python, cryptographically strong RNG is implemented in the
secrets
module. Let’s modify the code above to make the private key generation secure!That is amazing. I bet you wouldn’t be able to reproduce this, even with access to my PC. But can we go deeper?
Specialized sites
There are sites that generate random numbers for you. We will consider just two here. One is random.org, a well-known general purpose random number generator. Another one is bitaddress.org, which is designed specifically for Bitcoin private key generation.
Can random.org help us generate a key? Definitely, as they have service for generating random bytes. But two problems arise here. Random.org claims to be a truly random generator, but can you trust it? Can you be sure that it is indeed random? Can you be sure that the owner doesn’t record all generation results, especially ones that look like private keys? The answer is up to you. Oh, and you can’t run it locally, which is an additional problem. This method is not 100% secure.
Now, bitaddress.org is a whole different story. It’s open source, so you can see what’s under its hood. It’s client-side, so you can download it and run it locally, even without an Internet connection.
So how does it work? It uses you — yes, you — as a source of entropy. It asks you to move your mouse or press random keys. You do it long enough to make it infeasible to reproduce the results.
Are you interested to see how bitaddress.org works? For educational purposes, we will look at its code and try to reproduce it in Python.
Quick note: bitaddress.org gives you the private key in a compressed WIF format, which is close to the WIF format that we discussed before. For our purposes, we will make the algorithm return a hex string so that we can use it later for a public key generation.
Bitaddress: the specifics
Bitaddress creates the entropy in two forms: by mouse movement and by key pressure. We’ll talk about both, but we’ll focus on the key presses, as it’s hard to implement mouse tracking in the Python lib. We’ll expect the end user to type buttons until we have enough entropy, and then we’ll generate a key.
Bitaddress does three things. It initializes byte array, trying to get as much entropy as possible from your computer, it fills the array with the user input, and then it generates a private key.
Bitaddress uses the 256-byte array to store entropy. This array is rewritten in cycles, so when the array is filled for the first time, the pointer goes to zero, and the process of filling starts again.
Generate ssl certificate and key. Here we’ll use /root/certs: su - rootmkdir /root/certs && cd /root/certs.Create the certificate: openssl req -new -newkey rsa:4096 -x509 -sha256 -days 365 -nodes -out MyCertificate.crt -keyout MyKey.keyYou will be prompted to add identifying information about your website or organization to the certificate. That location will vary depending on your needs. Create the Certificate.Change to the root user and change to the directory in which you want to create the certificate and key pair. Since a self-signed certificate won’t be used publicly, this information isn’t necessary. If this certificate will be passed on to a certificate authority for signing, the information needs to be as accurate as possible.The following is a breakdown of the OpenSSL options used in this command.
The program initiates an array with 256 bytes from window.crypto. Then, it writes a timestamp to get an additional 4 bytes of entropy. Finally, it gets such data as the size of the screen, your time zone, information about browser plugins, your locale, and more. That gives it another 6 bytes.
Bitcoin Public Key Generator Using Seed Free
After the initialization, the program continually waits for user input to rewrite initial bytes. When the user moves the cursor, the program writes the position of the cursor. When the user presses buttons, the program writes the char code of the button pressed.
Finally, bitaddress uses accumulated entropy to generate a private key. It needs to generate 32 bytes. For this task, bitaddress uses an RNG algorithm called ARC4. The program initializes ARC4 with the current time and collected entropy, then gets bytes one by one 32 times.
This is all an oversimplification of how the program works, but I hope that you get the idea. You can check out the algorithm in full detail on Github.
Doing it yourself
For our purposes, we’ll build a simpler version of bitaddress. First, we won’t collect data about the user’s machine and location. Second, we will input entropy only via text, as it’s quite challenging to continually receive mouse position with a Python script (check PyAutoGUI if you want to do that).
That brings us to the formal specification of our generator library. First, it will initialize a byte array with cryptographic RNG, then it will fill the timestamp, and finally it will fill the user-created string. After the seed pool is filled, the library will let the developer create a key. Actually, they will be able to create as many private keys as they want, all secured by the collected entropy.
Initializing the pool
Here we put some bytes from cryptographic RNG and a timestamp.
__seed_int
and __seed_byte
are two helper methods that insert the entropy into our pool array. Notice that we use secrets
.Seeding with input
Here we first put a timestamp and then the input string, character by character.
Generating the private key
This part might look hard, but it’s actually very simple.
First, we need to generate 32-byte number using our pool. Unfortunately, we can’t just create our own
random
object and use it only for the key generation. Instead, there is a shared object that is used by any code that is running in one script.What does that mean for us? It means that at each moment, anywhere in the code, one simple
random.seed(0)
can destroy all our collected entropy. We don’t want that. Thankfully, Python provides getstate
and setstate
methods. So, to save our entropy each time we generate a key, we remember the state we stopped at and set it next time we want to make a key.Second, we just make sure that our key is in range (1,
CURVE_ORDER
). This is a requirement for all ECDSA private keys. The CURVE_ORDER
is the order of the secp256k1 curve, which is FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
.Finally, for convenience, we convert to hex, and strip the ‘0x’ part.
In action
Let’s try to use the library. Actually, it’s really simple: you can generate a private key in three lines of code!
You can see it yourself. The key is random and totally valid. Moreover, each time you run this code, you get different results.
Conclusion
As you can see, there are a lot of ways to generate private keys. They differ in simplicity and security.
Generating a private key is only a first step. The next step is extracting a public key and a wallet address that you can use to receive payments. The process of generating a wallet differs for Bitcoin and Ethereum, and I plan to write two more articles on that topic.
If you want to play with the code, I published it to this Github repository.
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I am making a course on cryptocurrencies here on freeCodeCamp News. The first part is a detailed description of the blockchain.
I also post random thoughts about crypto on Twitter, so you might want to check it out.