In the blockchain, every transaction has a transactionId where does this come from?

2 Answers 2


TXID is the double sha256 hash of the signed transaction, used to uniquely identify a particular transaction.

When you create/sign a transaction that hash will be generated with your transaction.

  • So it's the digital signature? Is there a comprehensive website that I can use to read up on bitcoin? From a programmers point of view. Commented Mar 15, 2018 at 20:28
  • Yeah, There's a book called Mastering Bitcoin by Andreas Antonopoulos , Best book ever.
    – Tailer
    Commented Mar 15, 2018 at 20:29
  • If TxId is the hash of the transaction data, how it is made unique to guard against fraudulent duplicate transactions (including timestamp)? Commented Dec 27, 2020 at 14:40
  • @HiranmayGhosh: The output of cryptographic hash functions is collision resistant and 2^256 is a huge space of numbers.
    – Murch
    Commented Dec 27, 2020 at 17:02
  • It is the double sha256. Commented Dec 29, 2020 at 12:19

The TXID is the hash of the transaction.

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