PSA: My phone just guessed my private key. If you use mobile (phone) wallets, clear your text prediction cache.

So, you know how when creating a new seed phrase in a wallet some apps make you reenter the entire seed?

Yeah, predictive typing remembers your used words and will suggest the second word as soon as you type the first one, especially if it's a word you not commonly use.

In my case my phone is in a different language than english as well, so it automatically adds typed words to the dictionary, which means my custom dictionary contains words in my language, and 24 english words...

This makes it easy to attack, get your hands on a phone, start any chat app, and start typing any words off the BIP39 list, and see what the phone suggests.

Do yourself a solid and prevent that from happening by clearing your predictive type cache.

Here's how to do it on Android:

https://intoput.com/clear-samsung-keyboard-history/

Here's how to do it on iPhone:

https://www.macworld.co.uk/how-to/how-remove-words-from-iphone-predictive-text-3642859/#:~:text=To%20reset%20your%20keyboard%20dictionary,%20head%20into%20your%20iPhone's%20settings,predictive%20words%20from%20showing%20up.

//EDIT: People are asking what app made me enter the entire thing. The wallet in question now presents a confirmation in the style of "confirm the 4th and 18th word by choosing from a list". Assuming they didn't update in the meantime, it is likely, I generated a wallet, wrote the seed down, deleted the wallet, and restored it from the written down seed to make sure I wrote it down correctly before transfering funds into it.

Also, I have played around with this for a bit. I have a Samsung phone with Android 12. This does not work (read: you schould not be vulnerable to it predicting every word in the correct order) if you use Gboard. On Samsung keyboard, it works if you have manually enabled "Auto replace" and "suggest text corrections". On Microsoft Swiftkey keyboard, it works(read: you are vulnerable) out of the box.

As I explained in a comment below, you can try it yourself. I did it with the phrase "I love eating bicycles at midnight". Open your browser on your phone. Into the search field, enter "I love eating". Note how your phone doesn't suggest "bicycles". Now finish the phrase and hit enter to search for it. Now close your browser, go into say, whatsapp, and start typing "I love" into a chat. Note the next word it suggests. Keep following the phrase to the end. It's fun!