In security news, I faced a new term related to hash functions: it is reported that the "in-house hash function" used in IOTA platform is broken (i.e. Curl-P hash function). You can find the complete paper introducing the vulnerability here.

But I do not understand if the term of "in-house" represents a specific type of hash function? And in general, what does "in-house" mean here?

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    I believe the definition of "In-house hash function" is "Don't use our product, we have no idea what we're doing". (see Steffen's answer for a less cheeky response) Nov 21, 2018 at 14:22
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    It means the same thing that "homeowner wiring" means to electricians. Nov 21, 2018 at 20:23
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    @EricLippert Be fair. There's less of a chance of a catastrophic fire and loss of life with homeowner wiring.
    – anon
    Nov 21, 2018 at 22:03
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    “in-house” is a term which, if heard several times at an interview causes one to lose desire to be offered the job. Generally speaking, “in-house” can be seen as the polar opposite of “industry standard”.
    – Mawg
    Nov 22, 2018 at 13:03

3 Answers 3


From the explanation of in-house in the Cambridge Directory: "Something that is done in-house is done within an organization or business by its employees rather than by other people".

Here it means developing your own hash algorithm instead of using a public one. Usually that means that it is developed by only a few people with only limited expertise in the problem area and without any public input. Thus it is very likely that the self-developed one gets eventually broken once more experts in cryptography take a look at it.

See also Why shouldn't we roll our own? and How valuable is secrecy of an algorithm?.

  • 76
    Hearing "in-house" with anything security related is always a HUGE red flag.
    – Marie
    Nov 21, 2018 at 16:35
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    And hearing "in-house" with anything crypto related is an even larger red flag even more often.
    – Maya
    Nov 21, 2018 at 21:47
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    Also see Is my developer's home-brew password security right or wrong, and why?, although I suspect Dave's algorithm was much, much worse than IOTA's.
    – jpmc26
    Nov 21, 2018 at 21:49
  • In short, in this context, "in-house" means "trouble"!
    – Muzer
    Nov 22, 2018 at 9:53

In the context of cryptography "in-house" is a synonym for "questionable origin and unverified strength".

It specifically means that they developed their own hashing function (or in other cases encryption, key-exchange scheme, etc.).

This, in cryptography, is a Bad Idea with capital letters. While developing your own library of common functions or your own webservice framework or whatever can have a perfectly good use-case, cryptography is one of the fields where a tiny mistake can make the whole thing incredibly fragile in a way that you will never find out. If you build your own webserver ("our high-performance in-house webserver...") and there's a problem, you have a good chance of finding out sooner rather than later because it crashes, or sends the wrong files, or performs badly. But if your crypto algorithm has a problem that destroys its cryptographic strength, you have to be very lucky that someone who breaks it actually tells you. The people who try to break it are almost certain to be attackers, because very few cryptographers waste their time on some in-house crypto hack. They know to stick with public algorithms where it actually matters if they find something, to more than one company.


I agree with the answer given an hour before this one about in-house meaning, "non-standard and probably not very sophisticated or rugged." There may still be one argument in favor of using an in-house hash. That is, it may be different enough from the standard ones out there that a hacker may decide it is too much work to figure out how to reverse engineer it. Even if you accept this argument, this sort of do-it-yourself approach should only ever be used to protect very low-value data.

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    This line of reasoning - relying on an attacker not knowing the implementation details and hoping that they won't find out - is named "Security by Obscurity". Since this is only a slowdown, rarely really a barrier, it is generally frowned upon and strongly recommended against. One area where it still does make sense is if your assets drop rapidly in worth in a short time (days to months) and an attack after one year is much less of an impact. Most game and movie DRM / copy protection schemes fall under this category.
    – Zefiro
    Nov 21, 2018 at 18:21
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    It's almost a trope at this point that whenever a "why is X bad?" question is posted, there will be an answer that says, paraphrasing, "well it's not that bad, because at least the attackers won't know how your version works". In other words, an appeal to Security by Obscurity. And yes, I get that this answer doesn't reject the premise, but others have done.
    – Tom W
    Nov 21, 2018 at 19:04
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    @Zefiro: There is a difference between "hoping that an attacker doesn't find out", and considering the cost/benefit ratios for possible attacks. To be sure, the risk of a popular encryption or hashing scheme being defeated may be slight, despite the level of research into attacks on them, but the probability of a scheme no prospective attackers would care about being defeated might be even lower.
    – supercat
    Nov 21, 2018 at 19:52
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    @Zefiro This reasoning is not about an attacker not knowing the implementation details. I think you need to read it again. It's about an attacker not having sufficient motivation to bother trying to break the algorithm. (It's still wrong, but not because it's security by obscurity, because it's not security at all. The problem is that you're very likely to drastically overestimate how much security you actually have, and that's exactly what happened here.) Nov 21, 2018 at 20:14
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    @supercat The problem is that normally, it's just security by obscurity. If you, say, shuffle an otherwise secure hash before storing (and unshuffle on retrieval and comparison), sure, that does extremely little for security, but it doesn't harm it. If all that's done is the shuffle, that's... very bad. And it's the latter case that's normally done, not the former. So people say "don't ever use it", because that's a good rule of thumb, and once you're experienced enough to know the difference, you're experienced enough to know when to ignore rules of thumb.
    – anon
    Nov 21, 2018 at 22:06

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