[Bitcoin-development] BIP 38 NFC normalisation issue

Jeff Garzik jgarzik at bitpay.com
Tue Jul 15 15:53:36 UTC 2014


On whitespace:  Security UX testing I've seen shows it is mentally
easier for some users to memorize and use longer passphrases, if they
are permitted spaces.  I've not seen anything written on use of
tabs/NLs/FFs in passphrases.

I can see the logic of some systems, that convert \s+ into ' ' for
purposes of password hashing, even though that might frustrate a
security nerd or two.
http://security.stackexchange.com/questions/32691/why-not-allow-spaces-in-a-password

I do think control characters should be filtered.

On Tue, Jul 15, 2014 at 11:32 AM, Andreas Schildbach
<andreas at schildbach.de> wrote:
> Can you provide the rationale for standard practice? For example, why
> should whitespace be allowed? I regularly use trim() on any passphrase
> (or other input ftm).
>
> So what's the action point? Should we amend the spec to filter control
> characters? That would get rid of the \u0000 problem.
>
>
> On 07/15/2014 05:17 PM, Jeff Garzik wrote:
>> Unicode guarantees that null-terminated strings still work.  U+0000
>> terminates a unicode (or C) string.  strlen() gets the string byte
>> count.  mbstowcs() gets the character count.
>>
>> Whitespace can be problematic, but should be allowed.  Control
>> characters should be filtered.  Emoticons probably cannot be filtered
>> without substandard approaches such as character blacklists, a road
>> you do not want to travel.
>>
>> (all this is simply standard practice)
>>
>>
>> On Tue, Jul 15, 2014 at 9:07 AM, Eric Winer <enwiner at gmail.com> wrote:
>>> I don't know for sure if the test vector is correct NFC form.  But for what
>>> it's worth, the Pile of Poo character is pretty easily accessible on the
>>> iPhone and Android keyboards, and in this string it's already in NFC form
>>> (f09f92a9 in the test result).  I've certainly seen it in usernames around
>>> the internet, and wouldn't be surprised to see it in passphrases entered on
>>> smartphones, especially if the author of a BIP38-compatible app includes a
>>> (possibly ill-advised) suggestion to have your passphrase "include special
>>> characters".
>>>
>>> I haven't seen the NULL character on any smartphone keyboards, though - I
>>> assume the iOS and Android developers had the foresight to know how much
>>> havoc that would wreak on systems assuming null-terminated strings.  It
>>> seems unlikely that NULL would be in a real-world passphrase entered by a
>>> sane user.
>>>
>>>
>>> On Tue, Jul 15, 2014 at 8:03 AM, Mike Hearn <mike at plan99.net> wrote:
>>>>
>>>> [+cc aaron]
>>>>
>>>> We recently added an implementation of BIP 38 (password protected private
>>>> keys) to bitcoinj. It came to my attention that the third test vector may be
>>>> broken. It gives a hex version of what the NFC normalised version of the
>>>> input string should be, but this does not match the results of the Java
>>>> unicode normaliser, and in fact I can't even get Python to print the names
>>>> of the characters past the embedded null. I'm curious where this normalised
>>>> version came from.
>>>>
>>>> Given that "pile of poo" is not a character I think any sane user would
>>>> put into a passphrase, I question the value of this test vector. NFC form is
>>>> intended to collapse things like umlaut control characters onto their prior
>>>> code point, but here we're feeding the algorithm what is basically garbage
>>>> so I'm not totally surprised that different implementations appear to
>>>> disagree on the outcome.
>>>>
>>>> Proposed action: we remove this test vector as it does not represent any
>>>> real world usage of the spec, or if we desperately need to verify NFC
>>>> normalisation I suggest using a different, more realistic test string, like
>>>> Zürich, or something written in Thai.
>>>>
>>>>
>>>>
>>>> Test 3:
>>>>
>>>> Passphrase ϓ␀𐐀💩 (\u03D2\u0301\u0000\U00010400\U0001F4A9; GREEK UPSILON
>>>> WITH HOOK, COMBINING ACUTE ACCENT, NULL, DESERET CAPITAL LETTER LONG I, PILE
>>>> OF POO)
>>>> Encrypted key: 6PRW5o9FLp4gJDDVqJQKJFTpMvdsSGJxMYHtHaQBF3ooa8mwD69bapcDQn
>>>> Bitcoin Address: 16ktGzmfrurhbhi6JGqsMWf7TyqK9HNAeF
>>>> Unencrypted private key (WIF):
>>>> 5Jajm8eQ22H3pGWLEVCXyvND8dQZhiQhoLJNKjYXk9roUFTMSZ4
>>>> Note: The non-standard UTF-8 characters in this passphrase should be NFC
>>>> normalized to result in a passphrase of0xcf9300f0909080f09f92a9 before
>>>> further processing
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>
>>>
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>>
>>
>>
>
>
>
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-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/




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