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2018-02-22crypto: speck - export common helpersEric Biggers1-41/+49
Export the Speck constants and transform context and the ->setkey(), ->encrypt(), and ->decrypt() functions so that they can be reused by the ARM NEON implementation of Speck-XTS. The generic key expansion code will be reused because it is not performance-critical and is not vectorizable, while the generic encryption and decryption functions are needed as fallbacks and for the XTS tweak encryption. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-02-22crypto: speck - add support for the Speck block cipherEric Biggers1-0/+299
Add a generic implementation of Speck, including the Speck128 and Speck64 variants. Speck is a lightweight block cipher that can be much faster than AES on processors that don't have AES instructions. We are planning to offer Speck-XTS (probably Speck128/256-XTS) as an option for dm-crypt and fscrypt on Android, for low-end mobile devices with older CPUs such as ARMv7 which don't have the Cryptography Extensions. Currently, such devices are unencrypted because AES is not fast enough, even when the NEON bit-sliced implementation of AES is used. Other AES alternatives such as Twofish, Threefish, Camellia, CAST6, and Serpent aren't fast enough either; it seems that only a modern ARX cipher can provide sufficient performance on these devices. This is a replacement for our original proposal (https://patchwork.kernel.org/patch/10101451/) which was to offer ChaCha20 for these devices. However, the use of a stream cipher for disk/file encryption with no space to store nonces would have been much more insecure than we thought initially, given that it would be used on top of flash storage as well as potentially on top of F2FS, neither of which is guaranteed to overwrite data in-place. Speck has been somewhat controversial due to its origin. Nevertheless, it has a straightforward design (it's an ARX cipher), and it appears to be the leading software-optimized lightweight block cipher currently, with the most cryptanalysis. It's also easy to implement without side channels, unlike AES. Moreover, we only intend Speck to be used when the status quo is no encryption, due to AES not being fast enough. We've also considered a novel length-preserving encryption mode based on ChaCha20 and Poly1305. While theoretically attractive, such a mode would be a brand new crypto construction and would be more complicated and difficult to implement efficiently in comparison to Speck-XTS. There is confusion about the byte and word orders of Speck, since the original paper doesn't specify them. But we have implemented it using the orders the authors recommended in a correspondence with them. The test vectors are taken from the original paper but were mapped to byte arrays using the recommended byte and word orders. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>