Pierluigi Paganini February 10, 2019

Google announced Adiantum, a new encryption method devised to protect Android devices without cryptographic acceleration.

Google announced Adiantum, a new encryption method devised to protect Android devices without cryptographic acceleration.

“Adiantum is an innovation in cryptography designed to make storage encryption more efficient for devices without cryptographic acceleration, to ensure that all devices can be encrypted.” reads the announcement published by Google.

Since Android version 6.0, user data are protected with Advanced Encryption Standard (AES) encryption, however, the feature is slow on mobile devices using low-end processors that haven’t hardware to support it.

The new encryption form has been created for devices running Android 9 and higher that doesn’t support AES CPU instructions.

For this reason, Google developed Adiantum that supports the ChaCha stream cipher in a length-preserving mode.
ChaCha allows improving security and performance in the absence of dedicated hardware acceleration.

Google experts pointed out that Adiantum encryption/decryption processes on ARM Cortex-A7 processors are around five times faster compared to AES-256-XTS.

“Unlike modes such as XTS or CBC-ESSIV, Adiantum is a true wide-block mode: changing any bit anywhere in the plaintext will unrecognizably change all of the ciphertext, and vice versa.  It works by first hashing almost the entire plaintext,” continues Google.

“We also hash a value called the “tweak” which is used to ensure that different sectors are encrypted differently. This hash is then used to generate a nonce for the ChaCha encryption. After encryption, we hash again, so that we have the same strength in the decryption direction as the encryption direction”  

Adiantum could represent the optimal solution for a wide range of devices that haven’t dedicated hardware for encryption, such as smartwatches, smart TVs, and other IoT devices running on Android OS.

“Our hope is that Adiantum will democratize encryption for all devices. Just like you wouldn’t buy a phone without text messaging, there will be no excuse for compromising security for the sake of device performance.”
wrote Eugene Liderman, Director of Mobile Security Strategy, Android Security & Privacy Team, says. 

“Everyone should have privacy and security, regardless of their phone’s price tag,”

Google published technical details about the new encryption form in the paper titled “Adiantum: length-preserving encryption for entry-level processors.”

Pierluigi Paganini

(SecurityAffairs – Android, encryption)

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