Android uses dm-crypt for disk encryption, and it is available since Android 3. And as you would know dm-crypt works at block device layer. So storage like YAFFS which works directly at nand flash chip level would not allow you to encrypt. But all other storage (which can be read block by block) can be encrypted.

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Android has been in the forefront of implementing data protection measures by offering encryption tools for its devices. Unfortunately, most users don’t know how to enable this feature. In fact, most Android users don’t even know what encryption does and why it is essential to encrypt mobile phones and other devices.

What is end-to-end encryption and how does it work

How does encryption work? Android phones do not automatically encrypt themselves, but Google makes it easy for the user to set up. Here's our guide on how to encrypt an Android device. Android uses dm-crypt for disk encryption, and it is available since Android 3. And as you would know dm-crypt works at block device layer. So storage like YAFFS which works directly at nand flash chip level would not allow you to encrypt. But all other storage (which can be read block by block) can be encrypted. The name and location of the encryption option will vary depending on your device manufacturer and Android version. Open the Settings app. Type security or encrypt in the app's search bar to find related settings. Tap the option to encrypt your device.