Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

Currently, circa. 5.8.0, the hashing value for a new hash is initialised to 0.

Would initialising this to a random 32-bit value chosen fresh for each hash at runtime, largely elleviate if not entirely suppress the possibility of a hash_clash attack against a perl hash-based system?

Whilst it would still be possible to compute 48 generators that could be combined as described in the article for any given initialisation of the hash, computing them for all possible 2**31 possible initialisations would be considerably more expensive. Finding a way of determining which initialisation had been randomly chosen for any given hash, of any given start of any given program on any given system renders choosing the right set of 48 generators almost impossible?

Or am I missing something obvious again?

Update:The change I was proposing would affect the following code from hv.c:59 (as of 5.8.0).

@hv.h - 5.8.0 #define PERL_HASH(hash,str,len) \ STMT_START { \ register const char *s_PeRlHaSh_tmp = str; \ register const unsigned char *s_PeRlHaSh = (const unsigned char *) +s_PeRlHaSh_tmp; \ register I32 i_PeRlHaSh = len; \ - register U32 hash_PeRlHaSh = 0; \ /* Randomise the initialisation (Pseudo code only:) */ + register U32 hash_PeRlHaSh = rand(0xFFFFFFFF); \ while (i_PeRlHaSh--) { \ hash_PeRlHaSh += *s_PeRlHaSh++; \ hash_PeRlHaSh += (hash_PeRlHaSh << 10); \ hash_PeRlHaSh ^= (hash_PeRlHaSh >> 6); \ } \ hash_PeRlHaSh += (hash_PeRlHaSh << 3); \ hash_PeRlHaSh ^= (hash_PeRlHaSh >> 11); \ (hash) = (hash_PeRlHaSh + (hash_PeRlHaSh << 15)); \ } STMT_END

Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller

In reply to Re: Hash Clash on purpose by BrowserUk
in thread Hash Clash on purpose by John M. Dlugosz

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others rifling through the Monastery: (7)
    As of 2015-11-29 12:06 GMT
    Find Nodes?
      Voting Booth?

      What would be the most significant thing to happen if a rope (or wire) tied the Earth and the Moon together?

      Results (750 votes), past polls