[Cryptography] Blockchain without proof of work

[Patrick Chkoreff]

Ángel wrote on 1/11/19 6:57 PM:

> I am a bit worried by the truncation part. The fact that a hash function
> is collision-resistant does NOT mean that the first N-bits (in your case
> 25) are as collision resistant as the whole hash.
> Thus, you may find for instance that a SHA2 truncated to 128 bits is
> actually suffering more collisions than a "weaker" MD5.

That I don't understand.  If taking the first 128 bits of SHA-512 is
less collision-resistant than some other 128 bit hash, wouldn't that
indicate a serious flaw in SHA-512?


-- Patrick