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myarbrough@oreilly.com 2014-11-18 07:21:04 -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 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: 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] [latexmath]