BitcoinCash/specification
1
Fork 0
Code Issues Pull Requests Releases Activity

Updated multiple pages to be 1 sentence per line.

Browse Source 
Updated the following files:

contributors.md
protocol/blockchain/transaction.md
project-history.md
target-audience.md
protocol/blockchain/hash.md
This commit is contained in:
Josh Green
2019-12-22 11:20:49 -05:00
committed by bitcoin
parent ce14cd4d98
commit 0d0a122c8f
5 changed files with 60 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files
protocol/blockchain/hash.md
+24 -11
View File
@@ -1,25 +1,38 @@
# Hashes
# Hash
A variety of hashing algorithms are used throughout the Bitcoin Cash protocol. In this specification we will not get into what hashes are, nor the details of the specific hashing algorithms used, as that is covered well elsewhere. Instead, this page will focus on which hashing algorithms are used, where they are used, and why they are used there.
A variety of hashing algorithms are used throughout the Bitcoin Cash protocol.
This specification does not explain what hashes are, nor the details of the specific hashing algorithms used, as that is covered well elsewhere.
Instead, this page will focus on which hashing algorithms are used, where they are used, and why they are used there.
## SHA-256
[SHA-256](https://en.wikipedia.org/wiki/SHA-2) is widely used throughout the Bitcoin Cash protocol to identify blocks and transactions along with a variety of purposes in transaction scripts. The most notable uses of SHA-256 are:
[SHA-256](https://en.wikipedia.org/wiki/SHA-2) is widely used throughout the Bitcoin Cash protocol to identify blocks and transactions along with a variety of purposes in transaction scripts.
The most notable uses of SHA-256 are:
- Block Hashing (Double SHA-256)
- A SHA-256 hash is taken of the block header. The output hash is then hashed again with SHA-256. This resultant hash is referred to simply as the block hash and is used as a unique identifier for the block.
- This double hash removes the possibility of a [length extension attack](https://en.wikipedia.org/wiki/Length_extension_attack) which a single SHA-256 is vulnerable to. While this is generally not a problem for Bitcoin Cash since the pre-image (the actual data of the block) is available, it trades a minor amount of inefficiency for confidence that this property of SHA-256 cannot be exploited.
- Double SHA-256 has it's own operation for ease-of-use, [OP_HASH256](/protocol/blockchain/script/opcodes/op-hash256)
- A SHA-256 hash is taken of the block header.
The output hash is then hashed again with SHA-256.
This resultant hash is referred to simply as the block hash and is used as a unique identifier for the block.
- This double hash removes the possibility of a [length extension attack](https://en.wikipedia.org/wiki/Length_extension_attack) which a single SHA-256 is vulnerable to.
While this is generally not a problem for Bitcoin Cash since the pre-image (the actual data of the block) is available, it trades a minor amount of inefficiency for confidence that this property of SHA-256 cannot be exploited.
- Double SHA-256 has its own Bitcoin [Script](/protocol/blockchain/script) operation for ease-of-use, [OP_HASH256](/protocol/blockchain/script/opcodes/op-hash256)
- Transaction Hashing (Double SHA-256)
- Transactions are also hashed using a double application of SHA-256. This is referred to as the transaction hash and is used to uniquely identify the transaction. (NOTE: Historical transaction hashes are not universally unique, there are two sets of two identical coinbase transactions and thus repeated hashes. Since [BIP-34](/protocol/forks/bip-0034), the block height is now required to be in the coinbase transaction, so this should not be possible in the future.)
- Transactions are also hashed using a double application of SHA-256.
This is referred to as the transaction hash and is used to uniquely identify the transaction.
(NOTE: Historical transaction hashes are not universally unique, there are two sets of two identical coinbase transactions (and thus identical hashes).
Since [BIP-34](/protocol/forks/bip-0034), the block height is now required to be in the coinbase transaction, which drastically reduces the possibility of duplicate transaction hashes in the future.)
- The two cases where this occurred are the following transactions which each appear in two blocks:
- <code>D5D27987D2A3DFC724E359870C6644B40E497BDC0589A033220FE15429D88599</code>
- <code>E3BF3D07D4B0375638D5F1DB5255FE07BA2C4CB067CD81B84EE974B6585FB468</code>
- `D5D27987D2A3DFC724E359870C6644B40E497BDC0589A033220FE15429D88599`
- `E3BF3D07D4B0375638D5F1DB5255FE07BA2C4CB067CD81B84EE974B6585FB468`
## RIPEMD-160
[RIPEMD-160](https://en.wikipedia.org/wiki/RIPEMD) is used in Bitcoin Cash scripts to create short, quasi-anonymous representations of payees for transactions. Since its brevity is also a potential liability for the anonymity it provides (since shorter hashes generally provide less collision-resistance), it is used in conjunction with SHA-256 when generating an address from a public key. That is, <code>(public key) -> SHA-256 -> RIPEMD-160 -> (address)</code>. This SHA-256 then RIPEMD-160 process has its own operation for ease-of-use, [OP_HASH160](/protocol/blockchain/script/op-codes/op-hash160).
[RIPEMD-160](https://en.wikipedia.org/wiki/RIPEMD) is used in Bitcoin Cash scripts to create short, quasi-anonymous representations of payees for transactions.
Since its brevity is also a potential liability for the anonymity it provides (since shorter hashes generally provide less collision-resistance), it is used in conjunction with SHA-256 when generating an address from a public key.
That is, `(public key) -> SHA-256 -> RIPEMD-160 -> (address)`.
This SHA-256 then RIPEMD-160 process has its own operation for ease-of-use, [OP_HASH160](/protocol/blockchain/script/op-codes/op-hash160).
## Murmur
[MurmurHash](https://en.wikipedia.org/wiki/MurmurHash) is used in Bitcoin to support [Bloom filters](https://en.wikipedia.org/wiki/Bloom_filter). The specific version used is the MurmurHash version 3 (32-bit), with the first hash initialized to <code>(numberOfHashesRequired * 0xFBA4C795L + nonce)</code> where <code>nonce</code> is a randomly chosen 32-bit unsigned integer.
[MurmurHash](https://en.wikipedia.org/wiki/MurmurHash) is used in Bitcoin to support [Bloom filters](https://en.wikipedia.org/wiki/Bloom_filter).
The specific version used is the MurmurHash version 3 (32-bit), with the first hash initialized to `(numberOfHashesRequired * 0xFBA4C795L + nonce)` where `nonce` is a randomly chosen 32-bit unsigned integer.
protocol/blockchain/transaction.md
+21 -3
View File
@@ -1,6 +1,13 @@
# Transaction
A transaction is how transfers are made in the blockchain. It comprises of a set of [transaction inputs](#transaction-inputs) which will be spent to a set of [transaction outputs](#transaction-outputs). The blockchain mining and full node software ensures that every transaction follows the blockchain's rules before admitting the transaction into a block. Verification of a transaction ensures that the inputs have not already been spent, that the total number of satoshis, the smallest quantity of Bitcoin Cash, provided as input is greater than or equal to the number of satoshis output (any extra is given to the miner as a transaction fee), and that the transaction is syntactically and cryptographically valid.
A Transaction is how bitcoins are transferred on the blockchain.
It comprises of a set of [Transaction Inputs](#transaction-inputs) which will be spent to a set of [Transaction Outputs](#transaction-outputs).
The mining nodes and full node software ensures that every transaction follows the blockchain's rules before admitting a transaction into a block.
Verification of a transaction ensures that:
- The Transaction Inputs have not already been spent.
- The total value contained in the Transaction Inputs is greater than (or equal) to the value specified within the Transaction Outputs.
- The Transaction is syntactically and cryptographically valid, and that the previous Unspent Transaction Outputs' [Locking Script](/protocol/blockchain/transaction/locking-script)s are correctly unlocked via the Transaction Inputs' [Unlocking Script](/protocol/blockchain/transaction/unlocking-script).
## Format
@@ -15,7 +22,10 @@ A transaction is how transfers are made in the blockchain. It comprises of a set
## Transaction Inputs
Transaction inputs are the "debits" of Bitcoin Cash and not only designate the satoshis that will be transferred as a part of the transaction, but they also provide proof of ownership via the [unlocking script](/protocol/blockchain/transaction/unlocking-script). A transaction input references a unspent transaction output, or UTXO, from a prior transaction. If a transaction would like to spend multiple UTXOs, it must have multiple inputs, one for each UTXO.
Transaction inputs are the "debits" of Bitcoin Cash and not only designate the satoshis that will be transferred as a part of the transaction, but they also provide proof of ownership via the [Unlocking Script](/protocol/blockchain/transaction/unlocking-script).
A Transaction Input references an unspent Transaction Output (oftern referred to as a "UTXO"), from a prior transaction.
If a Transaction would like to spend multiple UTXOs, it must have multiple inputs, one for each UTXO.
The Transaction Output that is being spent by a Transaction Input is often referred to as the "PrevOut", short for the "Previous Output".
### Format
@@ -28,7 +38,11 @@ Transaction inputs are the "debits" of Bitcoin Cash and not only designate the s
## Transaction Outputs
Transaction outputs are the "credits" of Bitcoin Cash. Each transaction output denotes a number of satoshis and the requirements are spending them. These requirements take the form of a [locking script](/protocol/blockchain/transaction/locking-script) and can equate to anything from the satoshis only being spendable by the owner of a specific private key, to anyone being able to spend them, to no one being able to spend them. While a transaction output has not been spent by another transaction (i.e. had its locking script "unlocked" by an input of a valid transaction) it is referred to as an unspent transaction output, or UTXO. After the output has been spent, it is referred to as a previous output, or PrevOut.
Transaction outputs are the "credits" of Bitcoin Cash.
Each transaction output denotes a number of satoshis and the requirements are spending them.
These requirements take the form of a [locking script](/protocol/blockchain/transaction/locking-script) and can equate to anything from the satoshis only being spendable by the owner of a specific private key, to anyone being able to spend them, to no one being able to spend them.
While a transaction output has not been spent by another transaction (i.e. had its locking script "unlocked" by an input of a valid transaction) it is referred to as an unspent transaction output, or UTXO.
A Transaction Output that is being spent by a Transaction Input is often referred to as the "PrevOut", short for the "Previous Output".
### Format
@@ -37,3 +51,7 @@ Transaction outputs are the "credits" of Bitcoin Cash. Each transaction output
| value | 8 bytes | unsigned integer<sup>[(LE)](/protocol/misc/endian/little)</sup> | The number of satoshis to be transferred. |
| locking script length | variable | [variable length integer](/protocol/formats/variable-length-integer) | The size of the unlocking script in bytes. |
| locking script | variable | bytes<sup>[(BE)](/protocol/misc/endian/big)</sup> | The contents of the locking script. |
## Transaction Fees
Extra satoshis from the Transaction Inputs that are not accounted for in the Transaction Outputs may be collected by the miner as the transaction fee.