Sure! If everything crypto were as simple as hashing, but protocol design and in particular privacy is not.
I was thinking along the lines of Bruce Schneier's infamous “Attacks always get better, they never get worse”.
In terms of hashes, md5 was once pretty secure. But we can't go back in time, we can't unlearn how to create hash collisions. And we can't force the world to only use 8 bit, 16 bit hardware from the 90s when brute forcing.
If the privacy of EU citizens were to solely rely on securely designed crypto of around a public ledger consider that 20 years of unbreakable crypto might be too little. What if every transaction you made 20 years ago was accessible to anyone? What if in 25 years they figured out how to make changes and no one could tell which one was authentic?
Sounds like scifi? Would probably be trivial for a block chain based on good old trusted DES.
