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Merge pulls #1105 and #1118

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- #1105: Dev Docs: drop mention of endianness in hash byte order
- #1118: Dev Docs: update v4 blocks text; mention version bits
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David A. Harding 2015-10-30 10:35:36 -04:00
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_includes/devdoc/bitcoin-core/api-intro.md
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@ -12,23 +12,23 @@ http://opensource.org/licenses/MIT.
{% autocrossref %}
Bitcoin Core RPCs accept and return hashes in the reverse of their
normal byte order. For example, the Unix `sha256sum` command would display the
SHA256(SHA256()) hash of mainnet block 300,000's header as the
following string:
Bitcoin Core RPCs accept and return the byte-wise reverse of computed
SHA-256 hash values. For example, the Unix `sha256sum` command displays the
SHA256(SHA256()) hash of mainnet block 300,000's header as:
> /bin/echo -n '020000007ef055e1674d2e6551dba41cd214debbee34aeb544c7ec670000000000000000d3998963f80c5bab43fe8c26228e98d030edf4dcbe48a666f5c39e2d7a885c9102c86d536c890019593a470d' | xxd -r -p | sha256sum -b | xxd -r -p | sha256sum -b
5472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc820000000000000000
The string above is also how the hash appears in the
The result above is also how the hash appears in the
previous-header-hash part of block 300,001's header:
<pre>02000000<b>5472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc82000\
0000000000000</b>ab0aaa377ca3f49b1545e2ae6b0667a08f42e72d8c24ae\
237140e28f14f3bb7c6bcc6d536c890019edd83ccf</pre>
However Bitcoin RPCs use the reverse byte order for hashes, so if you
However, Bitcoin Core's RPCs use the byte-wise reverse for hashes, so if you
want to get information about block 300,000 using the `getblock` RPC,
you need to reverse the byte order:
you need to reverse the requested hash:
> bitcoin-cli getblock \
000000000000000082ccf8f1557c5d40b21edabb18d2d691cfbf87118bac7254
@ -37,26 +37,19 @@ you need to reverse the byte order:
data, which is why the reversed string looks somewhat mangled.)
The rationale for the reversal is unknown, but it likely stems from
Bitcoin's use of hash digests (which are byte arrays in C++) as integers
Bitcoin Core's use of hashes (which are byte arrays in C++) as integers
for the purpose of determining whether the hash is below the network
target. Whatever the reason for reversing header hashes, the reversal
also extends to other hashes used in RPCs, such as TXIDs and merkle
roots.
Off-site documentation such as the Bitcoin Wiki tends to use the terms
big endian and little endian as shown in the table below, but they
aren't always consistent. Worse, these two different ways of
representing a hash digest can confuse anyone who looks at the Bitcoin
Core source code and finds a so-called "big endian" value being stored
in a little-endian data type.
As header hashes and TXIDs are widely used as global identifiers in
other Bitcoin software, this reversal of hashes has become the standard
way to refer to certain objects. The table below should make clear where
each byte order is used.
|---------------+---------------------|-----------------|
| Data | Internal Byte Order ("Big Endian") | RPC Byte Order ("Little Endian") |
| Data | Internal Byte Order | RPC Byte Order |
|---------------|---------------------|-----------------|
| Example: SHA256(SHA256(0x00)) | Hash: 1406...539a | Hash: 9a53...0614 |
|---------------|---------------------|-----------------|