Auto-completion functionality for seed phrase entry provides real benefit to the
user, reducing the number of keystrokes required and permitting quick re-entry
of mistyped words. In addition, unifying the number of keystrokes among words
improves security against acoustic side-channel attacks. To this end, three
new interactive mnemonic entry modes are introduced by this patch.
Each entry mode is optimized for a particular wordlist. The “short” mode, for
example, takes advantage of the fact that each word in the Monero wordlist is
uniquely identifiable by its first three letters. For MMGen’s default Electrum
wordlist, which lacks this unique substring property, the “minimal” mode was
developed to reduce keystrokes to a minimum while retaining the option of
obfuscating entry with pad characters.
Users who prefer not to use auto-completion may specify the “full” mode, which
emulates the previous default behavior.
Overview of the key entry modes:
- 'full' (all wordlists): words are typed in full and entered with the ENTER
or SPACE key, or by exceeding the pad character limit (see below).
- 'short' (BIP39, Monero): words are entered automatically once user types
UNIQ_SS_LEN (see below) valid word letters. 3-letter words in the BIP39
wordlist must be entered with the ENTER or SPACE key, or by exceeding the
pad character limit.
- 'fixed' (BIP39, Electrum): words are entered automatically once user types
UNIQ_SS_LEN characters in total. Words shorter than UNIQ_SS_LEN must be
padded to fit. Thus the total number of characters entered is the same for
all words.
- 'minimal' (Electrum): words are entered automatically once user types the
minimum number of characters required to uniquely identify a word (varies
from word to word). Words that are substrings of other words in the wordlist
must be entered with the ENTER or SPACE key, or by exceeding the pad
character limit. This is the only mode that checks user input letter by
letter.
Pad character limits by mode:
-----------------------------
short: 16
minimal: 16
full: longest_word - word_len
fixed: uniq_ss_len - word_len
Wordlist parameters:
--------------------
Parameter Electrum BIP39 XMRSEED
--------- -------- ----- -------
uniq_ss_len: 10 4 3
shortest_word: 3 3 4
longest word: 12 8 12
optimum mode: minimal fixed short
Default modes for each wordlist may be configured in 'mmgen.cfg' via the
'mnemonic_entry_modes' option.
Usage / testing:
$ mmgen-walletconv -i words
$ mmgen-walletconv -i bip39
$ mmgen-tool mn2hex_interactive fmt=mmgen mn_len=12 print_mn=1
$ mmgen-tool mn2hex_interactive fmt=bip39
$ mmgen-tool mn2hex_interactive fmt=xmrseed
$ test/unit_tests.py mn_entry
$ test/test.py -e input
