Mobile keyboard "predictive text" feature perfectly reproduces mnemonic phrases, cybersecurity professionals urge clearing cache and disabling predictive function.

Cybersecurity professional Redditor Andre accidentally discovered that the predictive text feature on his smartphone guessed the mnemonic phrase for his Bitcoin wallet. He shared the process and solutions for Android and iOS phones respectively.

"Predictive Text" Guessing Recovery Seed Phrases

Redditor Andre previously shared this surprising cybersecurity issue on Reddit, mentioning that the recovery seed phrases refer to the 2,048 randomly generated words in the Bitcoin Improvement Proposal (BIP) 39.

Andre pointed out that the predictive text function on smartphones suggests the next word after the user inputs the first word of the recovery seed phrase. This indicates that the smartphone has recorded the user's input into a personalized dictionary, allowing it to accurately suggest/predict 12-24 words.

Based on his testing:

• Google Keyboard Gboard: No impact, but users should still check if the predictive function is manually enabled.
• Samsung Keyboard: Requires manual activation of "Auto Replace Text" and "Suggest Corrections" to start recording.
• Microsoft SwiftKey: Starts recording upon download and activation of the app.

Clearing Predictive Text Cache

Although fully predicting all recovery seed phrases and their order may still be challenging, Andre pointed out that if someone malicious gains access to a phone, they could open any chat app, input any word from the BIP39 list, and view the suggested words given by the phone. He emphasized the importance of security, urging users to clear the predictive text cache and take preventive measures.

Users can follow these steps based on their situation:

1. Check if the phone can predict recovery seed phrases:

After typing the first word of the recovery seed phrase, does the second word suggestion appear? Andre emphasized that English is not the primary language on his phone, so when it inputs English words, the phone automatically saves less common words.

2. Clear predictive cache and disable predictive text function

For Samsung Keyboard, clearing keyboard history requires a reset as follows:

• General Settings
• Language and Input
• Keyboard, select Samsung Keyboard
• Reset
• Clear Personalized Predictions
• Click Clear

Refer to the Samsung Taiwan website for instructions on disabling the predictive text function.

For iPhone users, the operation to clear keyboard history is as follows:

• General
• Transfer or Reset iPhone
• Click Reset, not Erase All Content and Settings
• Click Reset Keyboard Dictionary

Note that this action will erase all word suggestions, so please consider it carefully.

For predictive text reference, visit the Apple official website or go to General Settings, Keyboard, and turn off "Predictive Text."