20200623, 01:43  #177  
"Robert Gerbicz"
Oct 2005
Hungary
1393_{10} Posts 
Quote:


20200623, 02:32  #178 
"Mihai Preda"
Apr 2015
29·41 Posts 
To allow portable verification of proofs, producers/verifiers must agree exactly on the hash algorithm (identical hash output). To make software errors less likely, it's best not to share the code but to use independent implementations. That's why I try to keep the hash schema simple, to make it easy to specify and independently implement correctly. I don't see yet why it's beneficial to have the hash be prime.

20200623, 03:01  #179  
P90 years forever!
Aug 2002
Yeehaw, FL
7×1,021 Posts 
Quote:
Quote:
I haven't coded any hash algorithms yet, pending an agreement on algorithm. My proofofconcept hash_function is h0=const, h[i]=(prev_hash + 15). I have plenty other work to do. 

20200623, 04:23  #180  
"Pavel Atnashev"
Mar 2020
43 Posts 
Quote:
Quote:
This works only for prime numbers and is easy to prevent, just require gcd(random,N1)=1. Alternatively, if N1 has specific form, you can test just specific factors. Proth N1 is very smooth, Mersenne N1 has divisors that look like Mersenne numbers themselves (if I understand correctly). Also consider the possible real world scenarios, which apply to all such cheating schemes. If you going to cheat with 1/1000 chance of success, you better hit it at the first time. Because if you fail, instead of being credited with a prime find you'll be banned from the prime universe. 

20200623, 05:00  #181  
"Mihai Preda"
Apr 2015
29·41 Posts 
Quote:
Quote:
For the hash algorithm, the question still stands whether any hardening is needed. Unless hardening in shown to be needed, the simple truncation of SHA3256 of the agreedupon size should be used as being the simplest. 

20200623, 08:13  #182 
"Pavel Atnashev"
Mar 2020
43 Posts 
I use 64bit md5 with no divisors <1000 "just in case". But I see the appeal of shorter unhardened hashes. Server load is linear with hash size.

20200623, 09:12  #183  
"Robert Gerbicz"
Oct 2005
Hungary
7×199 Posts 
Quote:
Is it intended? You could do this also in disk (using the same size). 

20200623, 11:13  #184  
"Mihai Preda"
Apr 2015
29×41 Posts 
Quote:
Edit: I missed "on the stack". I think they are not on the stack, but on the heap (gwalloc/gwfree) Last fiddled with by preda on 20200623 at 11:19 

20200623, 15:30  #185 
"Pavel Atnashev"
Mar 2020
43 Posts 
Bruteforce attack:
Code:
for (h0 = 1; h0 < max_hash; h0++) { y = x^(h0*h0); u_1 = x^(h0); if (hash(y) == h0) break; } u_i[i>1] = 1; 
20200623, 19:08  #186  
"Will Edgington"
Nov 2010
Utah, USA
24_{10} Posts 
Possible flexible file format
The ecm program (which uses libgmp) has a simple format for P1 and P+1 save files:
Code:
METHOD=P+1; B1=4299950000; N=71214505243381290342289358884062903424409248782929244751545497061659676830181069893652125357260888204241872521545920863671266091156523160599053871978101713571014846232692265302193576 41629634637632902818929376633641165995708421341209033069328278856607776384578328080846029713646218471064646270016968312691054210973840071649700163924918271; X=0x41a4cc7860dfb15fcdd98bcdbccc9b8b63796ad4e38c6fb055 967b800ea0c27fb8c1b5ff8f2a1d87c50196bc5869ced0d93597a447d7f7e233ead9e7036256b64a1ce7720274b605632205655335a629c10691284cce6ef7528b871a71e7e022c4ccc5a152b6e6b858dcda73ba0fde2f769912d837a4b164d5626ad62bc0752b2f7a1 73626a51231ba139d12; CHECKSUM=3059612973; PROGRAM=GMPECM 7.0.4; Y=0x0; X0=0xf7b36de6; Y0=0x0; WHO=wedgingt@wedgingt; TIME=Thu Apr 11 13:58:53 2019  Will Quote:


20200623, 21:54  #187  
"Mihai Preda"
Apr 2015
29·41 Posts 
Quote:
The attack would be somuchmore less practical for 48 or 64 bit hash. So, I'd take the above attack more like an indication of "lack of a practical attack", right? Last fiddled with by preda on 20200623 at 21:55 

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