I would like to know how transaction hash is determined.
For example,
https://blockchain.info/tx/278090c755aa016483ab3a9e6bffe1d2dfbf5b53edb7099b9946bc9dfe59f217. How does the network generate the underlined text? I searched Google but there is no answer - there was one in 2012. The explanation is way too complicated for me to understand.
I'm doing this on top of my head with a little help from the web, so may have some mistake, but these are the steps:
1. Transactions are encoded as (some data bytes):
- a 32 bit 'nVersion'
- a list of input transactions, vin
- a list of output transactions, vout
- a 32 bit 'nLockTime'
2. string all those together end to end (some data bytes as a string or block of text)
3. Taking the sha256 hash of this
4. Taking the sha256 hash of this (again)
You can combine step 3 and 4, sha256(sha256(input)). You do not have to know all the details of sha256 but you should learn the principles of hashing.
Then you have the transaction hash. Bitcoin uses the endian encoding, bytewise reversed.
Example with Genesis block:
Step 1)
nVersion: 01000000
inputs
count: 01
1st input:
prevout_hash: 0000000000000000000000000000000000000000000000000000000000000000
prevout_n: ffffffff
scriptSig: 4d:04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73
sequence: ffffffff
outputs
count: 01
1st output:
value: 00f2052a01000000 (hex(50*10^8) is 0000012a05f200, and bitcoin puts the bytes in reverse order)
scriptPubKey: 43:4104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac
nLockTime: 00000000
Step 2)
01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff4d04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73ffffffff0100f2052a01000000434104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac00000000
Step 3+4) (double sha256)
4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b
Have a look at pybitcoin tools
https://github.com/vbuterin/pybitcointools, you can easily create transaction hashes with that.
