EXT4/Fscrypt Changes For Linux 4.18: Speck File-System Encryption Being Added

Theodore Ts'o at Google submitted the feature updates today for the EXT4 file-system and FSCRYPT file-system encryption framework updates for the Linux 4.18 kernel merge window.

On the EXT4 side are many clean-ups and bug fixes, including better dealing with supported EXT4 file-systems. Those changes are mostly routine maintenance work and nothing too dramatic.

But the FSCRYPT changes are going to be more controversial for this file-system encryption support relied upon by EXT4, F2FS, etc. The main change with the FSCRYPT support in Linux 4.18 is adding support for Speck128/Speck256 as supported algorithms.

The Speck crypto work was added for the Linux 4.17 kernel and now would be an option for file-system encryption with FSCRYPT-backed file-systems for Linux 4.18. Speck though, for the uninitiated, was developed at the US National Security Agency (NSA). This cipher is quite controversial due to the NSA withholding details on some aspects of its design and some alleging that the NSA has lied or fabricated details about Speck. Long story short, some believe Speck could be back-doored by the NSA or at the very least weak to attacks and not trustworthy due to originating at a US spy agency. The NSA states that Speck and the hardware-focused Simon ciphers were designed for delivering an acceptable level of encryption on low-power IoT hardware.

Ted Ts'o admits that Speck is controversial, but he says it's being added for the "lowest-end Android devices" where there is no other encryption option supported. Ted Ts'o followed up with, "This is really intended for "The Next Billion Users"; phones like Android Go that was disclosed at the 2017 Google I/O conference, where the unsubsidized price is well under $100 USD (so cheaper than the original OLPC target)." Basically, super-cheap, super low-end smartphones using old ~ARMv7 SoCs lacking hardware encryption extensions and Speck is the most efficient algorithm they currently have for at least offering some level of file-system encryption.

The FSCRYPT pull request with the Speck addition and other clean-ups can be viewed here. We'll see what ends up happening, but with Speck having been added last cycle to the Crypto subsystem, it will probably be allowed into FSCRYPT especially with it coming at Google's behest.