Go to
https://aesencryption.net/ (something my or your mom would find on the internet), input the seed words, encrypt, count the number of characters.
I don't to visit any website. I know how AES works behind the scenes. I don't care what a random website outputs on an arbitrary input.
Your pRoPosEd method either involves a) external/online software to do
No, it doesn't. Check
openssl for example. It comes with literally every linux distro out there.
b) storing it digitally in a file for easier copy-paste into said external software
Not true.
or c) writing down 100-300 random hard-to-read Base64 characters on a piece of paper, case-sensitive, and hoping for no human error when typing it into said external software (and on paper!).
As shown in my previous post, a 12 word mnemonic results in 48 byte which can be easily represented by 48 characters.
My method [...] and yes, security through obscurity [...]
That is
one reason why it is bad.
Another one is that
it leaks bits of the plain text.
Any of these 2 reasons is enough to deem that as a bad design.
A wrench attack is the only thing my method is really vulnerable to
It's not.
Simply cryptanalysis and even bruteforcing is enough to break your "scheme".
It might work for you, you can feel safe as much as you want.
Trust me, no one here cares about you and your coins.
Just stop pretending your "mechanism" is good. It is not even close to being acceptable.