Ethereum message signing hex preview incorrect

[fabioberger]

When signing this message on a Ledger Nano S:

0x21c78f55e3f54ab5d872bfea03ad05d7bfb3d35dc1a537fd3ae731cdbb9bea21

which is the result of running:

0x3bd03be584f9df8a79ed49d8502c63d5fcff148157544242ffdbcc2b64321b1e

through:

keccak256("\x19Ethereum Signed Message:\n" + len(message) + message))

I am shown the following "message hash" on the Ledger Nano S display when prompted to confirm the signing:

1DAO...8EEE

When I'd expect to be shown:

21C7...EA21

If I disregard this discrepancy and sign the message anyway and verify the v, r, s values with the message I sent to the Ledger, I can verify that it is in-fact the message that was signed. The signature is valid for the expected value.

Why is this other "message hash" being presented to the user? Where does it come from? Any clarity on this would be great since we want our users to be able to confirm that they are signing the exact message they think they are signing.

[btchip]

This other hash is the sha256 hash of the message you're signing - it has been implemented this way so the user can verify it using a third party hashing solution not aware of specific Ethereum rules if the message is long

[fabioberger]

Thanks for the reply @btchip, applying the sha256 to:

0x21c78f55e3f54ab5d872bfea03ad05d7bfb3d35dc1a537fd3ae731cdbb9bea21

returns:

C234EDC89887D503823DA1AFE86C669F4B7FCFC2DC2D44334B4B02E7ECB5F019

With the 0x prefix and:

C8A9EF7D671BBB549D7736780819BF6D383A42EE7B7F2A59DC173F8FE701CFFF

Without it.

Neither matches:

1DAO...8EEE

Can you show an example and which implementation of sha256 is being used?

[pollastri-pierre]

Hi you need to hash the actual data not it's ascii representation. 2017-08-09 10:51 GMT+02:00 Fabio Berger <notifications@github.com>:

…

Thanks for the reply @btchip <https://github.com/btchip>, applying the sha256 to: 0x21c78f55e3f54ab5d872bfea03ad05d7bfb3d35dc1a537fd3ae731cdbb9bea21 returns: C234EDC89887D503823DA1AFE86C669F4B7FCFC2DC2D44334B4B02E7ECB5F019 With the 0x prefix and: C8A9EF7D671BBB549D7736780819BF6D383A42EE7B7F2A59DC173F8FE701CFFF Without it. Neither matches: 1DAO...8EEE Can you show an example and which implementation of sha256 is being used? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACcnwAr31tgHR9YU3rEtkQy5vTX6KiJQks5sWXMogaJpZM4OxmDc> .

-- Pierre Pollastri.

[fabioberger]

@pollastri-pierre could you perhaps post an example?

[btchip]

here's a Python example

>>> x = "3bd03be584f9df8a79ed49d8502c63d5fcff148157544242ffdbcc2b64321b1e".decode('hex')
>>> import hashlib
>>> h = hashlib.sha256()
>>> h.update(x)
>>> h.digest().encode('hex')
'1da0d1ce808a922fd381994f85fb8da16f464e4078cc6a20899bbd9956ff8eee'

[fabioberger]

Ah thank you so much! That was really helpful! Now look at how nice our message signing explanation dialog will look for all the wonderful Ledger users out there 💃

[btchip]

Looking great 👍 so closing that one