Re: [Bitcoin-development] BIP 38 NFC normalisation issue

[Andreas Schildbach <andreas@schildbach.de>]

Here is a good article that helped me with what's going wrong:

http://www.oracle.com/technetwork/articles/javase/supplementary-142654.html

Basically, Java is stuck at 16 bits per char due to legacy reasons. They
admit that for a new language, they would probably use 32 (or 24?) bits
per char.

\u literals express UTF-16 encoding, so you have to use 16 bits. I
learned that for codepoint 0x010400, I could write "\uD801\uDC00", which
is the UTF-16 encoding of that codepoint.

Other languages have literals for codepoints. E.g. Python can use
u"\U00010400" or HTML has 𐐀  Unfortunately, Java is missing such
a construct (at least in Java6).


On 07/17/2014 12:59 PM, Mike Hearn wrote:
> Glad we got to the bottom of that. That's quite a nasty
> compiler/language bug I must say. Not even a warning. Still, python
> crashes when trying to print the name of a null character. It wouldn't
> surprise me if there are other weird issues lurking. Would definitely
> sleep better with a more restricted character set.
> 
> On 17 Jul 2014 00:04, "Andreas Schildbach" <andreas@schildbach.de
> <mailto:andreas@schildbach.de>> wrote:
> 
>     Please excuse me. I had a more thorough look at the original problem and
>     found that the only problem with the original test case was that you
>     cannot specify codepoints from the SMP using \u in Java. I always tried
>     \u010400 but that doesn't work.
> 
>     Here is a fix for bitcoinj. The test now passes.
> 
>     https://github.com/bitcoinj/bitcoinj/pull/143
> 
>     We can (and probably should) still need to filter control chars, I'll
>     have a look at that now again.
> 
> 
>     On 07/16/2014 11:06 PM, Aaron Voisine wrote:
>     > If I first remove \u0000, so the non-normalized passphrase is
>     > "\u03D2\u0301\U00010400\U0001F4A9", and then NFC normalize it, it
>     > becomes "\u03D3\U00010400\U0001F4A9"
>     >
>     > UTF-8 encoded this is: 0xcf93f0909080f09f92a9 (not the same as what
>     > you got, Andreas!)
>     >
>     > Encoding private key:
>     5Jajm8eQ22H3pGWLEVCXyvND8dQZhiQhoLJNKjYXk9roUFTMSZ4
>     > with this passphrase, I get a BIP38 key of:
>     > 6PRW5o9FMb4hAYRQPmgcvVDTyDtr6R17VMXGLmvKjKVpGkYhBJ4uYuR9wZ
>     >
>     > I recommend rather than simply removing control characters from the
>     > password that instead the spec require that passwords containing
>     > control characters are invalid. We don't want people trying to be
>     > clever and putting them in thinking they are adding to the password
>     > entropy.
>     >
>     > Also for UI compatibility across many platforms, I'm also in favor
>     > disallowing any character below U+0020 (space)
>     >
>     > I can submit a PR once we figure out why Andreas's passphrase was
>     > different than what I got.
>     >
>     > Aaron Voisine
>     > breadwallet.com <http://breadwallet.com>
>     >
>     >
>     > On Wed, Jul 16, 2014 at 4:04 AM, Andreas Schildbach
>     > <andreas@schildbach.de <mailto:andreas@schildbach.de>> wrote:
>     >> Damn, I just realized that I implement only the decoding side of
>     BIP38.
>     >> So I cannot propose a complete test vector. Here is what I have:
>     >>
>     >>
>     >> Passphrase: ϓ␀𐐀💩 (\u03D2\u0301\u0000\U00010400\U0001F4A9; GREEK
>     >> UPSILON WITH HOOK, COMBINING ACUTE ACCENT, NULL, DESERET CAPITAL
>     LETTER
>     >> LONG I, PILE OF POO)
>     >>
>     >> Passphrase bytes after removing ISO control characters and NFC
>     >> normalization: 0xcf933034303066346139
>     >>
>     >> Bitcoin Address: 16ktGzmfrurhbhi6JGqsMWf7TyqK9HNAeF
>     >>
>     >> Unencrypted private key (WIF):
>     >> 5Jajm8eQ22H3pGWLEVCXyvND8dQZhiQhoLJNKjYXk9roUFTMSZ4
>     >>
>     >>
>     >> Can someone calculate the encrypted key from it (using whatever
>     >> implementation) and I will verify it decodes properly in bitcoinj?
>     >>
>     >>
>     >>
>     >> On 07/16/2014 12:46 PM, Andreas Schildbach wrote:
>     >>> I will change the bitcoinj implementation and propose a new test
>     vector.
>     >>>
>     >>>
>     >>>
>     >>> On 07/16/2014 11:29 AM, Mike Hearn wrote:
>     >>>> Yes sorry, you're right, the issue starts with the null code point.
>     >>>> Python seems to have problems starting there too. It might work
>     if we
>     >>>> took that out.
>     >>>>
>     >>>>
>     >>>> On Wed, Jul 16, 2014 at 11:17 AM, Andreas Schildbach
>     >>>> <andreas@schildbach.de <mailto:andreas@schildbach.de>
>     <mailto:andreas@schildbach.de <mailto:andreas@schildbach.de>>> wrote:
>     >>>>
>     >>>>     Guys, you are always talking about the Unicode astral
>     plane, but in fact
>     >>>>     its a plain old (ASCII) control character where this
>     problem starts and
>     >>>>     likely ends: \u0000.
>     >>>>
>     >>>>     Let's ban/filter ISO control characters and be done with
>     it. Most
>     >>>>     control characters will never be enterable by any keyboard
>     into a
>     >>>>     password field. Of course I assume that
>     Character.isISOControl() works
>     >>>>     consistently across platforms.
>     >>>>
>     >>>>    
>     http://docs.oracle.com/javase/7/docs/api/java/lang/Character.html#isISOControl%28char%29
>     >>>>
>     >>>>
>     >>>>     On 07/16/2014 12:23 AM, Aaron Voisine wrote:
>     >>>>     > If the user creates a password on an iOS device with an
>     astral
>     >>>>     > character and then can't enter that password on a JVM
>     wallet, that
>     >>>>     > sucks. If JVMs really can't support unicode NFC then
>     that's a strong
>     >>>>     > case to limit the spec to the subset of unicode that all
>     popular
>     >>>>     > platforms can support, but it sounds like it might just
>     be a JVM
>     >>>>     > string library bug that could hopefully be reported and
>     fixed. I get
>     >>>>     > the same result as in the test case using apple's
>     >>>>     > CFStringNormalize(passphrase, kCFStringNormalizationFormC);
>     >>>>     >
>     >>>>     > Aaron Voisine
>     >>>>     > breadwallet.com <http://breadwallet.com>
>     <http://breadwallet.com>
>     >>>>     >
>     >>>>     >
>     >>>>     > On Tue, Jul 15, 2014 at 11:20 AM, Mike Hearn
>     <mike@plan99.net <mailto:mike@plan99.net>
>     >>>>     <mailto:mike@plan99.net <mailto:mike@plan99.net>>> wrote:
>     >>>>     >> Yes, we know, Andreas' code is indeed doing normalisation.
>     >>>>     >>
>     >>>>     >> However it appears the output bytes end up being
>     different. What
>     >>>>     I get back
>     >>>>     >> is:
>     >>>>     >>
>     >>>>     >> cf930001303430300166346139
>     >>>>     >>
>     >>>>     >> vs
>     >>>>     >>
>     >>>>     >> cf9300f0909080f09f92a9
>     >>>>     >>
>     >>>>     >> from the spec.
>     >>>>     >>
>     >>>>     >> I'm not sure why. It appears this is due to the
>     character from
>     >>>>     the astral
>     >>>>     >> planes. Java is old and uses 16 bit characters
>     internally - it
>     >>>>     wouldn't
>     >>>>     >> surprise me if there's some weirdness that means it
>     doesn't/won't
>     >>>>     support
>     >>>>     >> this kind of thing.
>     >>>>     >>
>     >>>>     >> I recommend instead that any implementation that wishes
>     to be
>     >>>>     compatible
>     >>>>     >> with JVM based wallets (I suspect Android is the same) just
>     >>>>     refuse any
>     >>>>     >> passphrase that includes characters outside the BMP. At
>     least
>     >>>>     unless someone
>     >>>>     >> can find a fix. I somehow doubt this will really hurt
>     anyone.
>     >>>>     >>
>     >>>>     >>
>     >>>>    
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