Curl is meant to be a lightweight crypto for IOT, a field of very active research. None of this is controversial to anyone that isn't looking for things to latch negativity onto.
This seems to contradict the researcher's own post [1]:
> We discovered a vulnerability in IOTA after reviewing their code on GitHub in July. We disclosed what we found to the IOTA team on July 14th, and have been in contact with them since then as we discovered new issues and exploits.
Finally, even if Curl is meant as a new, lightweight hash function, it was broken by differential cryptanalysis, not some novel, exotic attack vector. Sounds like it needs a lot of work before it's fit for purpose.
[1] https://medium.com/@neha/cryptographic-vulnerabilities-in-io...
https://blog.iota.org/curl-disclosure-beyond-the-headline-18...
This article also answers the wrong question. If the crytocurrency is not cryptographically secure all that stands between an attacker and a victim is a piece of malware or social engineering. The fact that the researchers didn't go all the way and document a specific attack that could be performed tomorrow does not mean that Curl was secure in practice.
Finally this continues to fail to address many salient points. Like why use trits? Why wasn't kekkac used from day one?
> "The replacement Kerl hash function is unmodified KECCAK-384 that only converts its input and output from/to 243 trits to 48 bytes using basic two’s complement. KECCAK-384 is well vetted and researched."
"Replacement" really does mean replacement, i.e. what they substituted in after the researchers successfully attacked their original hash function. (The new one is called "Kerl" and the old one is called "Curl", which seems confusing.)
I'm not sure how asserting that the replacement is well-researched addresses the OP's point that their history of (a) rolling their own hash function, and (b) not adequately considering differential cryptanalysis, is a red flag. True, that specific vulnerability can now be considered fixed, which might not be clear from the OP's post - but it's still evidence of incompetence, which doesn't bode well for the quality of the rest of their design.