[Bitcoin-development] BIP 38 NFC normalisation issue

Mike Hearn mike at plan99.net
Wed Jul 16 09:12:26 UTC 2014

I'm all for fixing bugs, but I know from bitter experience that outside the
BMP dragons lurk. Browsers don't even expose Unicode APIs at all. You end
up needing to ship an entire pure-js implementation, which can be too large
for some use cases (too much time sunk on that issue in my last job).

I'm hoping BIP 38 doesn't get widely used anyway, to be frank. People
moving private keys around by hand has caused quite a few problems in the
past, sometimes people lost money. It's better to work at the level of a
wallet and ideally ask people to move money using regular transactions. Way
less potential for errors.

Regardless, I'll file a JVM bug and see what the outcome is.

On Wed, Jul 16, 2014 at 12:23 AM, Aaron Voisine <voisine at gmail.com> 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
> On Tue, Jul 15, 2014 at 11:20 AM, Mike Hearn <mike at 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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