This feature derives a deterministic password from your seed, according to BIP-85 (with the recent changes proposed here). Generated passwords can be sent as keystrokes via USB to the host computer, effectively using Coldcard as specialized password manager.
In addition to deriving up to 10,000 distinct secure passwords, the Coldcard Mk4 can also type them into a computer by emulating a USB keyboard, and simulating the keystrokes needed to type the password.
Switching...shown on the screen.
Emulated Keystrokes are mapped to specific characters based on your host PC keyboard language settings. For Coldcard to be able to type the correct BIP-85 password your host computer MUST use language settings that corresponds to a QWERTY key layout, including number row directly above QWERTY:
1 2 3 4 5 6 7 8 9 0 - = Q W E R T Y U I O P [ ] \ A S D F G H J K L ; ' Z X C V B N M , . /
Passwords generated and shown on Coldcard will always be correct with respect to BIP-85. However, when sending keystrokes, for example on German keyboard, what was typed will not match the text that was generated and shown on Coldcard's screen.
For example, if the correct password is
zYLoepugzdVJvdL56ogNV but when used
with German keyboard language settings, what will be typed is
yZLoepugydVJvdL56ogNV. You can see that German keyboard is not
QWERTY, but it is QUERTZ (y and z are swapped).
Even with "non-standard" keyboard language settings, Coldcard always sends exact same keystrokes for specific password index. It is deterministic, as long the keyboard language settings do not change. However, BIP-85 won't be respected in this case.
Check BIP-85 for complete specification of the new addition to BIP-85.
Coldcard does not allow you to specify password length - we always use length of 21. Passwords of this length generated according to BIP will have approximately 126 bits of entropy. This is on par with bitcoin security model and therefore all passwords the Coldcard will generate are considered very strong.
Using below seed, path and index, we generate passwords shown in the table:
wife shiver author away frog air rough vanish fantasy frozen noodle athlete pioneer citizen symptom firm much faith extend rare axis garment kiwi clarify
Although the Coldcard is emulating a keyboard at the lowest possible level, for some reason occasionally high-level applications have trouble with our high-speed typing.
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