Secret key storage question

[Robert J. Hansen]

> Also, doing the math, I get the following for the suggested longest
> passphrase length (maybe you can point out what I've got wrong):

Provided the passphrase is totally random, then yes, a 20-glyph passphrase
would be about right.  If your passphrase is English, you're looking at 1.3
bits of entropy per glyph, or a 100-glyph passphrase.

Entropy estimation is hard.