Ethereum: Why does Bitcoin Core print SHA256 hashes (uint256) bytes in reverse order?

understanding of the hatch and the challenges of adjusting Sha-256 Ethereum

As a developer who works with Bitcoin core, it is one of the most common problems that have appeared, print hash-256 in reverse order. This phenomenon led to frustration among developers, especially during functional testing. In this article, we imitate why Core Bitcoin pushes hash-256 in reverse order and examine the ways to solve this problem.

Task Sha-256

SHA-256 (Secured Hash Hash Algorithm) is a cryptographic hash function designed to produce unique fingerprint fingerprints. These fingerprints are generated by acting as an entrance, applying the SHA-256 algorithm and creating a 256-bit output (64-momeal). In the Bitcoin core, the Ethash command uses this hash feature to generate the Merkle Blockchain tree and other cryptographic structures.

Why Sha-256 Hash print in reverse order

When converting Hashov Uint256 in chains using the" printf "format in the Bitcoin nucleus, the bytes will be transformed due to the chain printing method. More accurate:

1.

• When printing an unsigned integer using%Uis the most important byte (MSB) first, followed by the least significant byte (LSB).

• Inuint256, each byte represents an 8 -bit unsigned integer.

• In the default setting, whenUNT256is converted into chains from the Bitcoin nucleus due to this order of reverse exit.

Functional tests challenges

Reversed output can lead to confusion during functional testing. For example::

• When you compare two hashs using "Ethash Compare", the comparison can fail if the hash values ​​are not printed in the same order.

• In some tests, inversion could affect the expected behavior of cryptographic functions used by blockchain.

Solving the problem

You can use multiple solutions to solve this problem:

• Print hashy as hexadecimal chains : Useprintfx instead of%u ‘to print hashs as hexadecimal chains. This ensures that production is not perverted.

`Bash

Echou "0x1234567890abcdef" printf "%x"

• Use your own formatting function : Write your own format chain usingprintfwith the desired output format. For example, you can use%08xto print Hashov as 8 -digit hexadecimal chains.

Bash

Echou "0x1234567890abcdef" printf "%08x"

• Use theprintfcommand with a specific separator : You can enter your own separator between values ​​using the '-t printfoption. For example::

Bash

ETHASH printing -T, -Stdout "0x1234567890ABCDEF" | ... ...

`

By implementing these solutions or customizations, you should be able to solve the Hash-256 has in reverse order in the Bitcoin core and make sure your functional tests are correct.

ethereum first bitcoin