Stuart McLachlan
stuart at lexacorp.com.pg
Sat Mar 19 07:06:47 CDT 2011
That got my interest piqued. So I've just built a small DLL (13KB) to calculate SHA1 digests for either strings or files. All you need to use it is to put the DLL somewhere in your PATH such as %SYSTEMROOT\System32 and include a couple of declarations in your application. Declare Function SHA1StringDigest Lib "LXSHA1.DLL" Alias "SHA1STRINGDIGEST" (Message As String) As String Declare Function SHA1FileDigest Lib "LXSHA1.DLL" Alias "SHA1FILEDIGEST" (FileName As String) As String It correctly returns the test results below for either the string or a file containing the same data. If anyone wants a copy, let me know. -- Stuart On 19 Mar 2011 at 21:20, Stuart McLachlan wrote: > Using your SHA1 function, what message digests do you get for the > standard test cases: > > 1. abc > 2. abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq > > These should return: > > 1. A9993E36 4706816A BA3E2571 7850C26C 9CD0D89D > 2. 84983E44 1C3BD26E BAAE4AA1 F95129E5 E54670F1 > > See Examples 1 and 2 at > http://www.itl.nist.gov/fipspubs/fip180-1.htm > > > > -- > Stuart > > > On 19 Mar 2011 at 20:20, Stuart McLachlan wrote: > > > How are you creating your hash? > > > > Can you post a few examples of different data strings and colliding > > SHA1 hashes. I can probably make a lot of money out of them. > > AFAIK, no one other than you has found any. > > > > -- > > Stuart > > > > > > On 18 Mar 2011 at 22:08, jwcolby wrote: > > > > > In my databases I create SHA1 hashes to enable joining between > > > tables and pull identical records (identical for the fields > > > hashed). > > > I create: > > > > > > 1) A HashAddr of the zip5, zip4 and addr. IOW I simply append the > > > three values and feed them into SHa1 and out pops a number which I > > > store in a field in my table. > > > > > > 2) A HashFamily of the Zip5, Zip4, Addr ad LName. > > > > > > 3) A HashPerson of Zip5, Zip4, Addr, LName and FName. > > > > > > I am getting known collisions between different addresses (I have > > > discovered and investigated collisions) in my HashAddr when I have > > > many millions of addresses. I need to address this. > > > > > > Back when I made my design decisions (2004) my hardware consisted > > > of single core processors, 4 gigs ram, Windows x32 etc. Now I > > > have 8 cores, 32 gigs Ram, Windows X64 etc. IOW I was to a great > > > extent constrained by my hardware "back in the day" whereas I am > > > much less so now. > > > > > > I am about to redesign my process. > > > > > > I am considering simply appending in the city and state strings to > > > all of the inputs: Addr, City, St, Zip5, Zip4 as the address base > > > and then the same with LName and FName for the other two > > > respective hashes. > > > > > > The objective is to minimize hash collisions, not prevent some > > > crypto attack. I use these hash fields to join between multi > > > million record tables so If I need to discover info in TableA > > > where the HashAddr is the same as in TableB, I need the > > > probability of a collision between different addresses > > > (family/Person) to be as close to zero as I can get it. > > > > > > My questions are: > > > > > > 1) Whether anyone out there is using a hash in this manner? > > > 2) Has anyone seen a table of collision probability between > > > messages of a given (short) message length. My message is 9 > > > digits for the zip5/4 and the address could be something as short > > > as PO Box 1, or Apt 1. IOW the total message length of 14 is > > > pretty common. Adding the state would give me minimum message > > > lengths of only 16 and City would only add a few more characters. > > > 3) Does anyone know if just adding the same data back in again > > > would decrease the collision probability. IOW > > > Zip5,Zip4,Addr,City,St,Zip5,Zip4Etc. > > > > > > Any experience out there? > > > > > > > > > -- > > > John W. Colby > > > www.ColbyConsulting.com > > > _______________________________________________ > > > dba-VB mailing list > > > dba-VB at databaseadvisors.com > > > http://databaseadvisors.com/mailman/listinfo/dba-vb > > > http://www.databaseadvisors.com > > > > > > > > > > > > > > _______________________________________________ > > dba-VB mailing list > > dba-VB at databaseadvisors.com > > http://databaseadvisors.com/mailman/listinfo/dba-vb > > http://www.databaseadvisors.com > > > > > > > > _______________________________________________ > dba-VB mailing list > dba-VB at databaseadvisors.com > http://databaseadvisors.com/mailman/listinfo/dba-vb > http://www.databaseadvisors.com > >