Boost logo

Boost :

Subject: Re: [boost] [optional] operator<(optional<T>, T) -- is it wrong?
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2014-12-03 11:24:07

On Dec 2, 2014, at 7:31 PM, Niall Douglas <s_sourceforge_at_[hidden]> wrote:

> On 2 Dec 2014 at 17:40, Howard Hinnant wrote:
>>> Out of curiosity I went and looked up what Python did to solve this
>>> (here's the discussion: In the
>>> end, they simply XOR salted the hash with a cryptographically
>>> generated random number produced at process launch (source:
>>> and carried on with their previous algorithm.
>> Here is a very short python script:
>> which appears to recover those random salts for the process. I tried it
>> out on 2.7.5 and it appears to work really well.
> This is as expected, as Pythons before 3.3 require a special
> environment variable to be set to turn on the secure hash. Apparently
> many Python programs assume the order of the standard hash algorithm,
> so they couldn't just turn it on without years of warning about the
> change.
> I just tried your script on Python 3.4 and got 0 candidate solutions
> whereas 2.7 does yield solutions. I don't claim their chosen solution
> is foolproof, but Python probably does see a lot more untrusted
> inputs than probably C++ does. If there were a gaping security hole
> there, we would surely have heard about it.

More info on why this attack failed on Python 3.4:

These articles claim that Python 3.4 and forward have simply adopted SipHash.

For anyone interested, there is a hash_append-compatible implementation of the SipHash24 variant here, in the files siphash.h/siphash.cpp:

You can experiment with this code without getting into hash_append by simply doing:

#include <iostream>
#include <random>
#include <string>
#include "siphash.h"

    // initialize random seeding
    std::random_device rd;
    std::mt19937_64 eng{rd()};

    // initialize siphash object
    acme::siphash hash(eng(), eng());

    // get something to hash
    std::string s("some data”);

    // hash it
    hash(, s.size());
    auto key = static_cast<std::size_t>(hash);

    // output the hash
    std::cout << key << '\n';


Boost list run by bdawes at, gregod at, cpdaniel at, john at