<p>First of all the <code>sighashType</code> field with (or without) any bit fields is used in source data while for signing. The signature does not sign itself, but it signs <code>sighashType</code>. So, changing <code>sighashType</code> invalidates signature.</p>

<p>Second, the data for signature is created in different manner.</p>

CC BY-SA 3.0
2017-11-01T04:43:10.937Z
2017-11-01T04:43:10.937Z
amaclin
<p>BCC transactions are "replay-protected" by the SIGHASH_FORKID 0x40.
However why can't I take one such transaction, flip off the 0x40 bit and here's a valid transaction on the BTC chain?</p>

<p>I guess that bit enters into the signature somewhere, but where?</p>

<bitcoin-cash><replay-attack>
What prevents one from replaying a BCC transaction by nulling the SIGHASH_FORKID bit?
Gurg Hackpof
# What prevents one from replaying a BCC transaction by nulling the SIGHASH_FORKID bit?

(Asked by: username_0 on 2017-11-01)

BCC transactions are "replay-protected" by the SIGHASH\_FORKID 0x40.
However why can't I take one such transaction, flip off the 0x40 bit and here's a valid transaction on the BTC chain?

I guess that bit enters into the signature somewhere, but where?

**Tags:** bitcoin-cash, replay-attack


---

## 1 answers

### Answer by username_1 on 2017-11-01. Score: 4 | Accepted answer

First of all the `sighashType` field with (or without) any bit fields is used in source data while for signing. The signature does not sign itself, but it signs `sighashType`. So, changing `sighashType` invalidates signature.

Second, the data for signature is created in different manner.


---

