Implement fingerprint login method

[0140454]

Related issue: #229

In the current implementation, we have to enter password to open wallet.
To implement fingerprint login method, i think we need to save user password in a secure method for future use.

Therefore, in this commit, if user allows to open wallet using fingerprint, app will encrypt user password (not CrAzYpass) using RSA algorithm and save ciphertext in SharedPreferences.

On access to the wallet, user can touch fingerprint sensor to use saved password to unlock the wallet.

[Codivorous]

I feel like we should implement CrAzYpass on this as well, before it gets merged. But really good work!

[m2049r]

this is really nice!!

• please delete the keys/prefs for removed wallets - since wallets can be removed manually this should be done somewhere around LognFragment.loadList() (after filterList)
• please add the fingerprint switch to the "change password" code (prompt_changepw layout) to enable to turn this on/off after creation.
• from reading the code I think that a wallet named "MonerujoRSA" would use the CrAzYpass key. and so removing the wallet would also destroy all wallets' passwords. we should maybe rename this key to something like "wallet" and use "wallet-[Wallet Name]" for the wallet keys?
• we want to avoid someone using your finger to access your funds. it may be a good idea to allow fingerprint access only to open the wallet or "Receive Menu" in the wallet list. and require the passphrase for sending & viewing details (details in open wallet should need passphrase only if wallet was opened with fingerprint or - maybe easier - is openable by fingerprint). but a sub-average hacker can get around this software restriction easily (modify the github code to not request passphrase) which they can install since they have access to the device (otherwise they can't use the finger). so maybe we just add a security warning to the help.

[0140454]

About last item,
maybe we can pop up a security warning while user switches on "Allow to open wallet using fingerprint" ?

If you allow to open wallet using fingerprint, anyone who can get your fingerprint will have access to your funds.
For example, malicious user around you can unlock your wallet when you are asleep.

Are you sure to enable this function?

[m2049r]

Security warning is a good idea. Two small changes to your text:

• ... will have full access to your funds.
• For example, a malicious ...

[0140454]

Thanks for your correction.

Now, app will pop up security warning when user enables this function.

[m2049r]

actually, it's not totally true about replacing the app with a hacked one because the app signatures have to match. but I think the security warning is the way to go nonetheless.

[0140454]

You're right.
Let me implement the above-mentioned to provide best information security?

• If user opens wallet using fingerprint
  It has to verify the identity with password again when sending funds or viewing details.
  Other operations, such as receiving or just viewing wallet balance, don't need to verify the identity.
• If user opens wallet using password
  All is same as before.

[m2049r]

@erciccione this adds some new strings:

• prompt_fingerprint_auth
• bad_fingerprint
• generate_fingerprint_hint
• generate_fingerprint_warn

chinese is already done