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Date: Thu, 16 Jul 2015 11:23:59 +0200
From: Dmitry Khovratovich <>
To: "" <>
Subject: Re: [PHC] patents

That's sad. The MSR paper you mention is probably

On Thu, Jul 16, 2015 at 10:48 AM, Solar Designer <> wrote:

> Hi,
> Earlier this year, I became aware, from Jeremy Spilman, of 2 patents
> that might (or might not, I am not a patent lawyer) apply to purposeful
> use of yescrypt's ROM as a secret.  My understanding is that they do not
> apply to uses of a ROM for port-hardness, which is what I am primarily
> proposing it for.
> One of these patents is Jeremy's own on what he calls Blind Hashing,
> already discussed in here.  (It made me pretty sad and angry at first,
> as I think it's a good idea that is a pity to have taken away from the
> larger community until the patent expires.  Also, obviously several
> people were thinking of similar approaches, not just Jeremy.)
> IIRC, the Blind Hashing patent talks specifically about looking up extra
> "salts", so it is unclear to me (not being a patent lawyer and not
> having read the patent closely) if this language applies to simultaneous
> use of a RAM and ROM like yescrypt does where no intermediate tiny value
> (salt-like) is ever derived.  Hopefully not.  For upgraded hashes, with
> g > 0, there are obviously tiny intermediate values - the old,
> pre-upgrade hashes.  I don't know if it fits under "salts" per that
> patent or not.  But even if it does, it shouldn't apply when the ROM
> isn't being used as a secret, but is used e.g. for port-hardness.
> The other patent, which I also haven't read closely, covers an idea
> expressed in IIRC a Microsoft Research paper from several years ago.
> In the paper, it's essentially the same idea Steve Thomas proposed
> shortly before Passwords12 - a large ROM on a system connected at low
> bandwidth just sufficient for defensive use but not for quickly
> downloading the ROM.  (I don't have that paper reference handy at the
> moment.  I may dig it up and post later, or Jeremy may.)
> In both cases, the number of lookups was intended to be low - just
> sufficient to hopefully prevent at least 1 of them (in each one hash
> computation) from completing when an attacker has only a portion of the
> ROM (e.g. only 1/4 of it), for most candidate passwords tested.
> In yescrypt's use of ROM, the number of lookups is a lot higher, as
> needed to provide port-hardness.
> Overall, I feel these patents do not directly apply to yescrypt's ROM,
> and not at all to its primary intended use, yet I felt I needed to post
> about them in here.  I'd appreciate advice on whether/how to mention
> related yet likely not directly applying patents like that in a revised
> yescrypt specification document.
> Alexander

Best regards,
Dmitry Khovratovich

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