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Clarified hash endianness

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Added Bitcoin Cash treatment of hash endianness which differs from mainstream hash implementations.
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Paul Chandler
2020-03-25 03:11:54 -04:00
committed by bitcoin
parent 22b441b023
commit f4cdd5a4ac
1 changed files with 3 additions and 4 deletions
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protocol/blockchain/hash.md
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@@ -5,7 +5,6 @@ This specification does not explain what hashes are, nor the details of the spec
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:
@@ -25,14 +24,14 @@ Since [BIP-34](/protocol/forks/bip-0034), the block height is now required to be
- `D5D27987D2A3DFC724E359870C6644B40E497BDC0589A033220FE15429D88599`
- `E3BF3D07D4B0375638D5F1DB5255FE07BA2C4CB067CD81B84EE974B6585FB468`
In contrast to many hashing algorithm implementations, Bitcoin Cash block and transaction hashes are *displayed* and *sent over the network* using a little-endian representation.
This can be confusing when, for example, a block hash is treated as a big-endian integer during comparisons with the block difficulty for block validation or mining.
## 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, `(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
## 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 `(numberOfHashesRequired * 0xFBA4C795L + nonce)` where `nonce` is a randomly chosen 32-bit unsigned integer.