What does malleable mean in "transaction malleability"?

2

Does malleable mean modifiable?

If you can malleate a transaction you can modify some of its parts leaving the transaction as still valid (the signatures are not broken).

If you can malleate the transaction outputs you can modify the outputs.

If you can malleate the order of inputs you can modify the order of inputs.

But the bitcoin.stackexchange.com "transaction-malleability" tag says:

A property of Bitcoin transactions that allows them to be replicated with another transaction id before they are included in a block.

This confuses me. Does transaction have an ID at all, and if it does ID seems totally irrelevant?

croraf

Posted 2017-11-27T22:13:42.913

Reputation: 1 112

Answers

1

Malleability is ability to change the binary contents of transaction (that also includes its TXID) without invalidating it, by someone else after broadcast and before the confirmation in block.

amaclin

Posted 2017-11-27T22:13:42.913

Reputation: 5 763

Couldn't the word modifiable be used instead malleable, because this is just modifying the transaction in some way, if I understand correctly?croraf 2017-11-27T22:29:33.467

Hm. Let us take any txA and any txB. Can we say that txB is a modification of txA where all bytes of txA were modified to bytes of txB ? :))))amaclin 2017-11-27T22:40:31.483

Than the word change (changable) instead malleate (malleable). Malleable just sounds fancy, but in fact just means change the transaction?croraf 2017-11-27T22:42:04.957

3It's a standard term in cryptography. Malleability specifically refers to the ability to change a signature without being authorized to sign.Pieter Wuille 2017-11-27T22:59:52.330