20050414, 12:15  #1 
Apr 2005
3 Posts 
conversion to GF(2)
would it be possible to "convert"
GF(211921F4A73A3761B88323D6A34DF9E984D08FF25C491DF5DB3251310FAB9C36ACE903E01D41B9BF1EA5CBEAA79FD1D7036835E45933E34825B87C9AB45C2C4F^1) to GF(2), for utilizing Coppersmith's indexcalculus ? eg, convert from one GF representation to another, with all numbers converted to GF2, espeically the polynomial etc. Best Regards, Bud 
20050414, 13:45  #2  
Nov 2003
2^{6}·113 Posts 
Quote:
I will assume that the large hex number is prime. At least it is odd What do you mean by "convert"?? You are not changing representations within a fixed field; you are asking about some (hypothetical) relation between GF(p) and GF(2)??? You can conduct an index calculus attack on GF(p) by the number field sieve. The field given above would require a massive effort. Good luck. Can you clarify? 

20050414, 17:58  #3 
Apr 2005
3 Posts 
Dear Dr Silverman,
Perhaps this is a stupid question, but the question is: Is it possible to convert modular arithmetices (espcially) discrete logs in prime fields GF(p) to GF(2) representation ? Like if we have an diskrete log like a^x mod p = b (which is to solve for x) in a prime field GF(p)  all parameters a,b,x,p elements of this field. Is there any possibility to convert those number to GF(2) like a,b elements in GF(2), p probably the irreducible polynomial, with the goal to solve the log in this field ? 
20050414, 18:18  #4 
May 2004
2^{4}×5 Posts 
Is your question the following?
Does there exist a polynomialtime reduction from the problem "Discrete log in GF(p)" to the problem "Discrete log in GF(2^n)" ? I put the 2^n in there because I know of an *extremely* efficient algorithm to compute discrete logs in GF(2) Dave 
20050414, 18:35  #5 
Apr 2005
3 Posts 
Hello,
And thanks for the reply, the answer would indeed be yes, can we somehow translate our problem to GF(2) for usage of the powerful dlp solving algorithms which exists ? Are you talking about coppersmith's indexcalculus ? Best Regards 
20050414, 20:12  #6  
Nov 2003
2^{6}·113 Posts 
Quote:
by "convert modular arithmetic in prime fields to GF(2) representation". What do you mean by "convert"? by "representation". All finite fields of a given order are isomorphic. Thus, any map from GF(a) to GF(b) will either be surjective or injective, depending on the size of the fields. There will never exist a 11 map unless the sizes are the same. The only time solving a discrete log in one field helps to solve a DL in another is if the first field is a subfield of the second AND the target log in the second field is in the orbit of the generator used in the first field. May I suggest that you do some reading about the structure of Finite Fields? Lidl & Neiderreiter's book is superb. NFS *IS* an index calculus algorithm. One can solve logs in GF(p) with it. 

20050414, 21:17  #7  
Apr 2004
Copenhagen, Denmark
74_{16} Posts 
Quote:
 Cheers, Jes 

20050414, 21:26  #8  
Feb 2005
2^{2}·3^{2}·7 Posts 
Quote:
Quote:


20050415, 12:23  #9  
Nov 2003
1110001000000_{2} Posts 
Quote:
One must solve the matrix mod p1, not just mod p. 

20050416, 01:13  #10  
Aug 2002
101000000_{2} Posts 
Quote:


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