Unlike basic encryption as explained in the previous section, digital signatures are a bit more complicated. The goal of digital signatures is twofold:. If the two values do not match , then you as the receiver of data know that either the data was tampered with, or the sender of this data is not the same person whose public key you are decrypting everything with.
If the two values do match , then you know the data has not been tampered with. You know this because the data was hashed before being sent.
Since a hash function is a one-way function, if the data payload was altered in any way, taking a hash of it would equal a different result than what you decrypted from the signed data. Finally, you know that the sender of this data matches the public key you possess. Let's take a look at a practical example. First, we have a module that signs a message and encrypts it. This is the "sender" of data:. You can see that this module returns the entire "package" of data that we will send over the network. Now imagine this data was sent over some insecure network, and the receiver of the data used the following module to verify it:.
If you run this file, you should get the success message, because we are using the correct keypair! In our above example, you might have wondered why we are sending such a large piece of data over a network:. JWTs are becoming the de-facto method of authenticating users in web applications, and many JWTs use the method described above to transfer user data in a verifiable way.
You'll notice that a JWT has 3 parts separated by periods. The first part is the header, the second part is the payload, and the third part is the digital signature. If you pasted the above JWT into this tool and select the RS algorithm, you would get the following data back:.
I think so! Within this JWT, we have a header that specifies which JWT algorithm was used which also inherently indicates which hashing function to use on the data , a body that carries our data, and a signature that represents the following pseudocode below :. Again, this is not a definitive tutorial on JWTs, but I wanted to show the basics of them to demonstrate one of the many common use cases of public-key cryptography!!
Mini private key format
A hacker could sign some data with his private key and convince the receiver that his public key is the correct one! When the receiver of the data receives it, he will go through the process of verification described in the previous section, and since the hacker signed with his private key and you decrypted it with his public key, you would be none the wiser! Using the same verification method described above, a receiver of data can not only verify that the sender of data is who he says he is, but the receiver of data can also verify that the public key they are using has been issued by a trusted Certificate Authority.
For example, if you are creating a website that runs the HTTPS protocol, you need to register for a certificate. A common tool installed on many Apache2 servers is the letsencrypt utility, which allows you to register a free certificate with the company, Lets Encrypt. Public Key Cryptography allows data traveling on an insecure channel to either be encrypted sign with public key or signed sign with private key. By browsing the internet, you are indirectly using both of these use cases on a daily basis.
Not sure. Knowledge that makes you feel smart? Have a great day and drop me a comment if you enjoyed this post. Created a dev. Thank you for this fantastic write-up. Thaddeus - Oct 8 ' KatrinKunze - Oct 6 ' Luka Bubalo - Sep 21 ' David R. Myers - Sep 9 ' To resolve this issue, when private keys are exported from a wallet, the WIF that is used to represent them is implemented differently in newer bitcoin wallets, to indicate that these private keys have been used to produce compressed public keys and therefore compressed bitcoin addresses. This allows the importing wallet to distinguish between private keys originating from older or newer wallets and search the blockchain for transactions with bitcoin addresses corresponding to the uncompressed, or the compressed, public keys, respectively.
That is because the private key has an added one-byte suffix shown as 01 in hex in Table , which signifies that the private key is from a newer wallet and should only be used to produce compressed public keys. Private keys are not themselves compressed and cannot be compressed. Notice that the hex-compressed private key format has one extra byte at the end 01 in hex. While the Base58 encoding version prefix is the same 0x80 for both WIF and WIF-compressed formats, the addition of one byte on the end of the number causes the first character of the Base58 encoding to change from a 5 to either a K or L.
Think of this as the Base58 equivalent of the decimal encoding difference between the number and the number While is one digit longer than 99, it also has a prefix of 1 instead of a prefix of 9. As the length changes, it affects the prefix. In Base58, the prefix 5 changes to a K or L as the length of the number increases by one byte. Remember, these formats are not used interchangeably. In a newer wallet that implements compressed public keys, the private keys will only ever be exported as WIF-compressed with a K or L prefix.
Import Private Key from Bitcoin Paper Wallet to Bitcoin Core
If the wallet is an older implementation and does not use compressed public keys, the private keys will only ever be exported as WIF with a 5 prefix. The goal here is to signal to the wallet importing these private keys whether it must search the blockchain for compressed or uncompressed public keys and addresses. If a bitcoin wallet is able to implement compressed public keys, it will use those in all transactions. The private keys in the wallet will be used to derive the public key points on the curve, which will be compressed.
The compressed public keys will be used to produce bitcoin addresses and those will be used in transactions. When exporting private keys from a new wallet that implements compressed public keys, the WIF is modified, with the addition of a one-byte suffix 01 to the private key. They are not compressed; rather, WIF-compressed signifies that the keys should only be used to derive compressed public keys and their corresponding bitcoin addresses.
The code uses a predefined private key to produce the same bitcoin address every time it is run, as shown in Example If you used the uncompressed public key instead, it would produce a different bitcoin address 14K1y…. The most comprehensive bitcoin library in Python is pybitcointools by Vitalik Buterin. Example shows the output from running this code.
Example is another example, using the Python ECDSA library for the elliptic curve math and without using any specialized bitcoin libraries. Example shows the output produced by running this script. Example uses os. Caution: Depending on the OS, os. In the following sections we will look at advanced forms of keys and addresses, such as encrypted private keys, script and multisignature addresses, vanity addresses, and paper wallets.
Private keys must remain secret.
Importing vs Sweeping
The need for confidentiality of the private keys is a truism that is quite difficult to achieve in practice, because it conflicts with the equally important security objective of availability. Keeping the private key private is much harder when you need to store backups of the private key to avoid losing it. A private key stored in a wallet that is encrypted by a password might be secure, but that wallet needs to be backed up.
At times, users need to move keys from one wallet to another—to upgrade or replace the wallet software, for example. But what if the backup itself is stolen or lost? These conflicting security goals led to the introduction of a portable and convenient standard for encrypting private keys in a way that can be understood by many different wallets and bitcoin clients, standardized by BIP see Appendix C. BIP proposes a common standard for encrypting private keys with a passphrase and encoding them with Base58Check so that they can be stored securely on backup media, transported securely between wallets, or kept in any other conditions where the key might be exposed.
The standard for encryption uses the Advanced Encryption Standard AES , a standard established by the NIST and used broadly in data encryption implementations for commercial and military applications.
Mini private key format - Bitcoin Wiki
The result of the BIP encryption scheme is a Base58Check-encoded encrypted private key that begins with the prefix 6P. If you see a key that starts with 6P , it is encrypted and requires a passphrase in order to convert decrypt it back into a WIF-formatted private key prefix 5 that can be used in any wallet. Many wallet applications now recognize BIPencrypted private keys and will prompt the user for a passphrase to decrypt and import the key.
Third-party applications, such as the incredibly useful browser-based Bit Address Wallet Details tab , can be used to decrypt BIP keys. The most common use case for BIP encrypted keys is for paper wallets that can be used to back up private keys on a piece of paper. Test the encrypted keys in Table using bitaddress. They designate the beneficiary of a bitcoin transaction as the hash of a script, instead of the owner of a public key. The feature was introduced in January with BIP see Appendix C , and is being widely adopted because it provides the opportunity to add functionality to the address itself.
The requirements are designated at the time the address is created, within the script, and all inputs to this address will be encumbered with the same requirements. Encoding a P2SH address involves using the same double-hash function as used during creation of a bitcoin address, only applied on the script instead of the public key:.
P2SH is not necessarily the same as a multisignature standard transaction. A P2SH address most often represents a multi-signature script, but it might also represent a script encoding other types of transactions. Currently, the most common implementation of the P2SH function is the multi-signature address script. As the name implies, the underlying script requires more than one signature to prove ownership and therefore spend funds.
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For example, Bob the coffee shop owner from Chapter 1 could use a multisignature address requiring 1-of-2 signatures from a key belonging to him and a key belonging to his spouse, ensuring either of them could sign to spend a transaction output locked to this address. Or Gopesh, the web designer paid by Bob to create a website, might have a 2-of-3 multisignature address for his business that ensures that no funds can be spent unless at least two of the business partners sign a transaction.
We will explore how to create transactions that spend funds from P2SH and multi-signature addresses in Chapter 6. Vanity addresses are valid bitcoin addresses that contain human-readable messages. Vanity addresses require generating and testing billions of candidate private keys, until a bitcoin address with the desired pattern is found.