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Confirm: How to check bitcoin transaction id
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| How to check bitcoin transaction id | |
| How to check bitcoin transaction id | |
| How to check bitcoin transaction id |
TXID
The hash of a transaction's data.
A (Transaction ID) is basically an identification number for a bitcoin transaction.
Examples:
A is always 32 bytes (64 characters) and hexadecimal.
Creating a TXID
You get a by hashingtransaction data through SHA256 twice.
Searching for TXIDs in the blockchain.
If you’ve just hashed some transaction data and want to search for a TXID in the blockchain, you have to search for it in reverse byte order.
Why?
Because welcome to Bitcoin.
Due to historical accident, the tx and block hashes that bitcoin core uses are byte-reversed. I’m not entirely sure why. May be something like using openssl bignum to store hashes or something like that, then printing them as a number. – Wladimir van der Laan (Bitcoin Core developer)
In other words, this was a slight oversight in the early development of Bitcoin that has now become a standard.
Where are TXIDs used?
1. Searching the blockchain.
If you’ve just made a transaction, you can use the to find it in the blockchain. For example:
If you have been given a by your bitcoin wallet, it’s probably already in its “searchable” format (reverse byte order).
2. Spending outputs.
You use a when you want to use an existing output as an input in a new transaction.
Because after all, a is a unique identifier1 for a transaction.
Notes
Why hash twice? Why not once?
Things often get hashed twice in bitcoin for super-extra security.
SHA-256(SHA-256(x)) was proposed by Ferguson and Schneier in their excellent book “Practical Cryptography” (later updated by Ferguson, Schneier, and Kohno and renamed “Cryptography Engineering”) as a way to make SHA-256 invulnerable to “length-extension” attack. They called it “SHA-256d”. –
https://crypto.stackexchange.com/questions/779/hashing-or-encrypting-twice-to-increase-security/884#884
Hash functions like SHA256 are great for creating identification numbers, because they will take in any string of data and always spit out a short yet unique result.
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