如何创建与IPFS兼容的多哈希

问题描述

我正在尝试创建与IPFS兼容的mutihash，但是不匹配.我在这里问是因为我还没有找到一个从哈希到最终结果的例子.

I'm trying to create an IPFS compatible mutihash but it is not matching. I am asking here because I have not yet found an example that takes this from hashing to the end result.

echo -n multihash > multihash.txt


ipfs add multihash.txt
added QmZLXzjiZU39eN8QirMZ2CGXjMLiuEkQriRu7a7FeSB4fg multihash.txt


sha256sum multihash.txt
9cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47  multihash.txt

node

> var bs58=require('bs58')
bs58.encode(new Buffer('9cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47','hex'))
'BYptxaTgpcBrqZx9tghNCWFfUuYBcGfLydEvDjXqBV7k'

> var mh=require('multihashes')
mh.toB58String(mh.encode(new Buffer('9cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47','hex'), 'sha2-256'))
'QmYtUc4iTCbbfVSDNKvtQqrfyezPPnFvE33wFmutw9PBBk'

目的是使用多哈希程序包重新创建IPFS路径QmZLXzjiZU39eN8QirMZ2CGXjMLiuEkQriRu7a7FeSB4fg.

The intent is to re-create the IPFS path QmZLXzjiZU39eN8QirMZ2CGXjMLiuEkQriRu7a7FeSB4fg using the multihashes package.

我能够创建相同的哈希QmYtUc...9PBBk，如此处的示例所示: https://github.com/multiformats/multihash#example

I'm able to create the same hash QmYtUc...9PBBk as shown in the example here: https://github.com/multiformats/multihash#example

推荐答案

IPFS使用 multihash 格式，如下:

IPFS uses multihash where the format is the following:

哈希函数代码列表可以在此表中找到

The list of hash function codes can be found in this table.

以下是使用 SHA2-256 作为哈希函数的过程的一些伪代码

Here's some pseudocode of the process using SHA2-256 as the hashing function.

sha2-256   size  sha2-256("hello world")
0x12       0x20  0xb94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

将这三个项目串联起来会产生

Concatenating those three items will produce

1220b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

然后将其编码为 base58

QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4

---

以下是如何在JavaScript中实质上实现多哈希的示例:

const crypto = require('crypto')
const bs58 = require('bs58')

const data = 'hello world'

const hashFunction = Buffer.from('12', 'hex') // 0x20

const digest = crypto.createHash('sha256').update(data).digest()

console.log(digest.toString('hex')) // b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

const digestSize = Buffer.from(digest.byteLength.toString(16), 'hex')

console.log(digestSize.toString('hex')) // 20

const combined = Buffer.concat([hashFunction, digestSize, digest])

console.log(combined.toString('hex')) // 1220b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

const multihash = bs58.encode(combined)

console.log(multihash.toString()) // QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4

---

有一个CLI可用于生成多哈希:

$ go get github.com/multiformats/go-multihash/multihash
$ echo -n "hello world" | multihash -a sha2-256
QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4

---

如@David所说， IPFS中的文件被转换"为Unixfs文件"，这是 DAG .因此，当您使用add将文件上传到IPFS时，数据具有元数据包装器，当您对其进行多哈希处理时，它会给您带来不同的结果.

---

As @David stated, A file in IPFS is "transformed" into a Unixfs "file", which is a representation of files in a DAG. So when you use add to upload a file to IPFS, the data has metadata wrapper which will give you a different result when you multihash it.

例如:

$ echo -n "hello world" | ipfs add -Q
Qmf412jQZiuVUtdgnB36FXFX7xg5V6KEbSJ4dpQuhkLyfD

---

这是Node.js中的一个示例，该示例如何生成与ipfs add完全相同的多重哈希:

---

Here's an example in Node.js of how to generate the exact same multihash as ipfs add:

const Unixfs = require('ipfs-unixfs')
const {DAGNode} = require('ipld-dag-pb')

const data = Buffer.from('hello world', 'ascii')
const unixFs = new Unixfs('file', data)

DAGNode.create(unixFs.marshal(), (err, dagNode) => {
  if (err) return console.error(err)

  console.log(dagNode.toJSON().multihash) // Qmf412jQZiuVUtdgnB36FXFX7xg5V6KEbSJ4dpQuhkLyfD
})

---

希望这会有所帮助

---

Hope this helps

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