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myarbrough@oreilly.com 2014-11-18 07:21:37 -08:00
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@ -227,7 +227,7 @@ Most bitcoin implementations use the((("OpenSSL cryptographic library"))) http:/
The bitcoin address is what appears most commonly in a transaction as the "recipient" of the funds. If we were to compare a bitcoin transaction to a paper check, the bitcoin address is the beneficiary, which is what we write on the line after "Pay to the order of." On a paper check, that beneficiary can sometimes be the name of a bank account holder, but can also include corporations, institutions, or even cash. Because paper checks do not need to specify an account, but rather use an abstract name as the recipient of funds, that makes paper checks very flexible as payment instruments. Bitcoin transactions use a similar abstraction, the bitcoin address, to make them very flexible. A bitcoin address can represent the owner of a private/public key pair, or it can represent something else, such as a payment script, as we will see in <<p2sh>>. For now, let's examine the simple case, a bitcoin address that represents, and is derived from, a public key.
The bitcoin address is derived from the public key through the use of one-way cryptographic hashing. A "hashing algorithm" or simply "hash algorithm" is a one-way function that produces a fingerprint or "hash" of an arbitrary-sized input. Cryptographic hash functions are used extensively in bitcoin: in bitcoin addresses, in script addresses, and in the mining proof of work algorithm. The algorithms used to make a bitcoin address from a public key are the((("Secure Hash Algorithm (SHA)"))) Secure Hash Algorithm (SHA) and the((("RACE Integrity Primitives Evaluation Message Digest (RIPEMD)"))) RACE Integrity Primitives Evaluation Message Digest (RIPEMD), specifically((("RIPEMD160")))((("SHA256"))) SHA256 and RIPEMD160.
The bitcoin address is derived from the public key through the use of one-way cryptographic hashing. A "hashing algorithm" or simply "hash algorithm" is a one-way function that produces a fingerprint or "hash" of an arbitrary-sized input. Cryptographic hash functions are used extensively in bitcoin: in bitcoin addresses, in script addresses, and in the mining proof-of-work algorithm. The algorithms used to make a bitcoin address from a public key are the((("Secure Hash Algorithm (SHA)"))) Secure Hash Algorithm (SHA) and the((("RACE Integrity Primitives Evaluation Message Digest (RIPEMD)"))) RACE Integrity Primitives Evaluation Message Digest (RIPEMD), specifically((("RIPEMD160")))((("SHA256"))) SHA256 and RIPEMD160.
Starting with the public key K, we compute the SHA256 hash and then compute the RIPEMD160 hash of the result, producing a 160-bit (20-byte) number:
[latexmath]
@ -254,7 +254,7 @@ image::images/msbt_0405.png["pubkey_to_address"]
==== Base58 and Base58Check Encoding
In order to represent long numbers in a compact way, using fewer symbols, many computer systems use mixed-alphanumeric representations with a base (or radix) higher than 10. For example, whereas the traditional decimal system uses the 10 numerals 0 through 9, the hexadecimal system uses 16, with the letters A through F as the six additional symbols. A number represented in hexadecimal format is shorter than the equivalent decimal representation. Even more compact,((("Base-64 representation"))) Base-64 representation uses 26 lower-case letters, 26 capital letters, 10 numerals, and two more characters such as "\+" and "/" to transmit binary data over text-based media such as email. Base-64 is most commonly used to add binary attachments to email. Base58 is a text-based binary-encoding format developed for use in bitcoin and used in many other crypto-currencies. It offers a balance between compact representation, readability, and error detection and prevention. Base58 is a subset of Base64, using the upper- and lowercase letters and numbers, but omitting some characters that are frequently mistaken for one another and can appear identical when displayed in certain fonts. Specifically, Base58 is Base64 without the 0 (number zero), O (capital o), l (lower L), I (capital i), and the symbols "\+" and "/". Or, more simply, it is a set of lower and capital letters and numbers without the four (0, O, l, I) just mentioned.
In order to represent long numbers in a compact way, using fewer symbols, many computer systems use mixed-alphanumeric representations with a base (or radix) higher than 10. For example, whereas the traditional decimal system uses the 10 numerals 0 through 9, the hexadecimal system uses 16, with the letters A through F as the six additional symbols. A number represented in hexadecimal format is shorter than the equivalent decimal representation. Even more compact,((("Base-64 representation"))) Base-64 representation uses 26 lower-case letters, 26 capital letters, 10 numerals, and two more characters such as "\+" and "/" to transmit binary data over text-based media such as email. Base-64 is most commonly used to add binary attachments to email. Base58 is a text-based binary-encoding format developed for use in bitcoin and used in many other cryptocurrencies. It offers a balance between compact representation, readability, and error detection and prevention. Base58 is a subset of Base64, using the upper- and lowercase letters and numbers, but omitting some characters that are frequently mistaken for one another and can appear identical when displayed in certain fonts. Specifically, Base58 is Base64 without the 0 (number zero), O (capital o), l (lower L), I (capital i), and the symbols "\+" and "/". Or, more simply, it is a set of lower and capital letters and numbers without the four (0, O, l, I) just mentioned.
[[base58alphabet]]
.bitcoin's Base58 alphabet
@ -269,7 +269,7 @@ To add extra security against typos or transcription errors, Base58Check is a Ba
((("data, converting to Base58Check")))To convert data (a number) into a Base58Check format, we first add a prefix to the data, called the "version byte," which serves to easily identify the type of data that is encoded. For example, in the case of a bitcoin address the prefix is zero (0x00 in hex), whereas the prefix used when encoding a private key is 128 (0x80 in hex). A list of common version prefixes is shown in <<base58check_versions>>.
Next we compute the "double-SHA" checksum, meaning we apply the SHA256 hash-algorithm twice on the previous result (prefix and data):
Next, we compute the "double-SHA" checksum, meaning we apply the SHA256 hash-algorithm twice on the previous result (prefix and data):
----
checksum = SHA256(SHA256(prefix+data))
@ -277,7 +277,7 @@ checksum = SHA256(SHA256(prefix+data))
From the resulting 32-byte hash (hash-of-a-hash), we take only the first four bytes. These four bytes serve as the error-checking code, or((("checksum"))) checksum. The checksum is concatenated (appended) to the end.
The result is composed of three items, a prefix, the data, and a checksum. This result is encoded using the Base58 alphabet described previously. <<base58check_encoding>> illustrates the Base58Check encoding process.
The result is composed of three items: a prefix, the data, and a checksum. This result is encoded using the Base58 alphabet described previously. <<base58check_encoding>> illustrates the Base58Check encoding process.
[[base58check_encoding]]
.Base58Check encoding: a Base58, versioned, and checksummed format for unambiguously encoding bitcoin data