Proposal: Add the unordered-containers package and the hashable package to the Haskell Platform
Felipe Almeida Lessa
felipe.lessa at gmail.com
Wed Mar 20 18:08:02 CET 2013
Although I'd prefer a secure-by-default implementation, this is a good
compromise. Then unordered-containers' docs should reference
SipHashed in a prominent.
On Wed, Mar 20, 2013 at 2:02 PM, Thomas Schilling
<nominolo at googlemail.com> wrote:
> To make this more precise the next version of hashable (say, 1.3)
> would include this:
> newtype SipHashed a = SipHashed a
> class SipHashable a where
> sipHashWithSalt :: Int -> a -> Int
> instance SipHashable a => Hashable (SipHashed a) where
> hashWithSalt salt (SipHashed x) = sipHashWithSalt salt x
> Then all Hashable instances are taken from hashable-1.1. All Hashable
> instances from hashable-1.2 are renamed to become instances of
> Alternatively, hashable-1.2 could be renamed to hashable-sip-1.0 or so.
> Note that I do not propose to make this change now. We include
> hashable-1.1 now, and the above will be the upgrade path to include
> secure hashing.
> On 20 March 2013 16:47, Thomas Schilling <nominolo at googlemail.com> wrote:
>> OK. I think a reasonable approach would be the following:
>> - add hashable-1.1 (ie., without SipHash) to the platform
>> - later create a new release of hashable, that is fast by default and
>> provides SipHash functionality via a newtype wrapper (or it could be a
>> new package that defines the newtype and all the standard instances)
>> What's important is that the default behaviour (fast vs. secure) won't
>> change in a later version of the platform.
>> We should also make it clear that hashable (even with siphash) does
>> not aim to implement secure hashing. I.e., no replacement for proper
>> HMACs, SHA1, etc.
>> On 19 March 2013 16:51, Johan Tibell <johan.tibell at gmail.com> wrote:
>>> Hi Thomas,
>>> On Tue, Mar 19, 2013 at 8:41 AM, Thomas Schilling <nominolo at googlemail.com>
>>>> On 19 March 2013 16:01, Johan Tibell <johan.tibell at gmail.com> wrote:
>>>> > http://trac.haskell.org/haskell-platform/wiki/Proposals/unordered-containers
>>>> The links to the repos are wrong. It should be "tibbe" instead of
>>>> Bryan's recent change to change "hashable" to use SipHash is certainly
>>>> the right default. There were some complaints about performance for
>>>> use cases where security is not an issue. What are the options for
>>>> users that wish to use a different hash function? According to the
>>>> paper, SipHash is about 2x slower than CityHash.
>>> 2x is *a lot*. 2x is about the performance difference between Map and
>>> HashMap. Since the raison d'etre for HashMap is that it's faster than Map,
>>> if we'd see a 2x slowdown in HashMap there would be little reason to use it.
>>> For example, 'delete' for HashMap ByteString got almost 2x slower with
>>> hashable-1.2. Since 'delete' does more than just hashing, that means that
>>> SipHash is quite a bit slower than the current (insecure) hash function.
>>> Another example: with GHC 7.6.2 HashMap String is almost unusable slow (5x
>>> slower than before). This is likely due to a GHC bug, but it's something we
>>> need to investigate. At the moment I don't encourage people to upgrade to
>>> The right way to go is probably to make this a user decision. Many
>>> applications (e.g. data processing) has no need for the security guarantee
>>> so paying for it makes little sense.
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