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Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF

From "Jason A. Donenfeld" <Jason@zx2c4.com>
Newsgroups linux.kernel
Subject Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF
Date 2016-12-16 17:00 +0100
Message-ID <sP35n-5AA-1@gated-at.bofh.it> (permalink)
References <sONDj-3Jb-7@gated-at.bofh.it> <sORGV-6gY-3@gated-at.bofh.it> <sP07v-3Df-21@gated-at.bofh.it> <sP07v-3Df-19@gated-at.bofh.it> <sP35n-5AA-3@gated-at.bofh.it>
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Hi JP & George,

My function names:
- SipHash -> siphash
- HalfSipHash -> hsiphash

It appears that hsiphash can produce either 32-bit output or 64-bit
output, with the output length parameter as part of the hash algorithm
in there. When I code this for my kernel patchset, I very likely will
only implement one output length size. Right now I'm leaning toward
32-bit. Questions:

- Is this a reasonable choice?
- When hsiphash is desired due to its faster speed, are there any
circumstances in which producing a 64-bit output would actually be
useful? Namely, are there any hashtables that could benefit from a
64-bit functions?
- Are there reasons why hsiphash with 64-bit output would be
reasonable? Or will we be fine sticking with 32-bit output only?

With both hsiphash and siphash, the division of usage will probably become:
- Use 64-bit output 128-bit key siphash for keyed RNG-like things,
such as syncookies and sequence numbers
- Use 64-bit output 128-bit key siphash for hashtables that must
absolutely be secure to an extremely high bandwidth attacker, such as
userspace directly DoSing a kernel hashtable
- Use 32-bit output 64-bit key hsiphash for quick hashtable functions
that still must be secure but do not require as large of a security
margin

Sound good?

Jason

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Thread

Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 04:50 +0100
  Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 13:50 +0100
    Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 17:00 +0100
      Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 18:40 +0100
        Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 19:10 +0100
          Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 21:20 +0100
            Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF Theodore Ts'o <tytso@mit.edu> - 2016-12-16 21:50 +0100
              Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 23:20 +0100
                Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-17 00:50 +0100
                Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-17 02:50 +0100
                Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-17 03:20 +0100
                Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add  cryptographically secure PRF Theodore Ts'o <tytso@mit.edu> - 2016-12-17 16:50 +0100
                Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add  cryptographically secure PRF Jeffrey Walton <noloader@gmail.com> - 2016-12-17 17:20 +0100
                Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add  cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-19 18:30 +0100
              Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 23:20 +0100
                Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF Andy Lutomirski <luto@amacapital.net> - 2016-12-16 23:20 +0100
      Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-17 13:50 +0100
    Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF Tom Herbert <tom@herbertland.com> - 2016-12-16 20:50 +0100
      Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add  cryptographically secure PRF Daniel Micay <danielmicay@gmail.com> - 2016-12-16 21:50 +0100
        Re: [kernel-hardening] Re: [PATCH v5 1/4] siphash: add  cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 22:10 +0100
      Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-16 21:50 +0100
        Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF Tom Herbert <tom@herbertland.com> - 2016-12-16 22:00 +0100
      Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-17 16:30 +0100
        RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF David Laight <David.Laight@ACULAB.COM> - 2016-12-19 15:20 +0100
          RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF "George Spelvin" <linux@sciencehorizons.net> - 2016-12-19 19:20 +0100
    Re: [PATCH v5 1/4] siphash: add cryptographically secure PRF "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-16 21:50 +0100

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