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Android Verified Boot enforced with 7.0

Sami Tolvanen of Google posted a blog about Android Verified Boot and how things have changed with Android 7.0:

Android uses multiple layers of protection to keep users safe. One of these layers is verified boot, which improves security by using cryptographic integrity checking to detect changes to the operating system. Android has alerted about system integrity since Marshmallow, but starting with devices first shipping with Android 7.0, we require verified boot to be strictly enforcing. This means that a device with a corrupt boot image or verified partition will not boot or will boot in a limited capacity with user consent. Such strict checking, though, means that non-malicious data corruption, which previously would be less visible, could now start affecting process functionality more. By default, Android verifies large partitions using the dm-verity kernel driver, which divides the partition into 4 KiB blocks and verifies each block when read, against a signed hash tree. A detected single byte corruption will therefore result in an entire block becoming inaccessible when dm-verity is in enforcing mode, leading to the kernel returning EIO errors to userspace on verified partition data access. This post describes our work in improving dm-verity robustness by introducing forward error correction (FEC), and explains how this allowed us to make the operating system more resistant to data corruption. These improvements are available to any device running Android 7.0 and this post reflects the default implementation in AOSP that we ship on our Nexus devices.[…]

Full post:
http://android-developers.blogspot.com/2016/07/strictly-enforced-verified-boot-with.html

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