I would say probably not, since there were only 4 variations of a simple substitution cypher, e.g. you could encrypt some text with option 1-4, and to decrypt you picked option 1-4... i.e. anyone could decrypt using the barbie typewriter and a maximum of 4 attempts... not really secure at all.

>simple substitution cypher

And for those that are unaware, substitution ciphers have been unsecure for over a millennium now. So relying on nobody guessing you used a Barbie typewriter isn't an option either.

It's much worse than that. Simple substitution ciphers are as secure as writing in a custom font: you only have to figure out which letter is represented by each symbol. This is usually not difficult when using frequency analysis or, heck, even brute force with some dictionary lookups to see which attempt contained the most existing words.

> Would this have been useful for spies?

Not in the slightest. If you would rank all types of encryption by strength, this would be one of the weakest ones, right between writing the text upside down and choosing a custom font.

It's a little like Enigma, except that the substitution is static, not changing on each key press.

It's nothing like Enigma: no plugboard, no sequence of rotors that can be switched out, and (as you've noted) no new alphabet on each keypress.

Enigma is not that easy to crack, even today. I wouldn't compare it to a simple substitution cipher as to laymen that sounds like it was some pretty good shit even if it wasn't as good as Enigma.

I'm pretty sure I've seen somewhere a JS implementation of an enigma cracker...

Afaik it's still quite complex to run. But JS is quite an optimised language these days, so that might not be far from the C implementation...

It's a useful prop for spies posing as little girls. As seen on The Americans.