How Does a Change in One Bit of Input Affect the Hash Output?

A change in a single bit of the input data will result in a completely different hash output due to the 'avalanche effect,' a key property of cryptographic hash functions. This effect ensures that even a tiny modification to a transaction (e.g. changing one digit of the amount) results in a drastically different, unpredictable hash digest.

This property is crucial for the integrity check provided by ECDSA signatures, as the original signature will immediately fail verification against the new hash.