Hey Guys,

I’d like to propose a feature to bitcoin to solve the following problems:

- When people read or write private keys it is very easy to mistake a letter or number.

- When entering a private key a mistake isn’t identified until the entire key is entered.

- When an error is made in providing a private key the location of the error isn’t indicated within the private key.

- Private keys stored on paper can be lost if a single character is damaged or poorly transcribed.

First provide an option to use to the NATO phonetic alphabet when displaying or entertaining private keys. To indicate lower case the word should not be capitalized. Capital letters and numbers should be capitalized.

The nato phonetic alphabet is a long-standing international standard (as international as the use of letters and numbers already used in base58) and has been designed to make each letter easily distinguishable when spoken and written. 

By using whole words, that are easily distinguishable and from a very short word database (58 well known words that are either the English numbers or words that begin with the letter indicated) the likelihood of errors in recovery are reduced.

The second part of the solution is to insert checksum letters. If every 5th word is actually a checksum for the previous 4 words, you end up with 13 sentences such as:

ALFA tango THREE SIX bravo

In this case bravo is actually a checksum for the previous 4 words and can be calculated and verified as the private key is entered. If the user accidentally trumped BRAVO instead of bravo the checksum would immediately indicate an error within these 5 words (in most cases) making for a greatly improved user experience.

An additional side effect of this is that even if an entire word is lost on multiple lines, the  checksum would probably make guessing the correct words relatively easy.

I realize some of these issues have been discussed in relation to bip39, but I hope this is more likely to be adopted by bitcoin core as it uses existing private keys, has no impact on keygen, does not require a standardized and well known word list for every language, and is essential just a display format that hopefully wouldn’t require invasive code changes.

Thanks in advance for your feedback.

-JW