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Hash-Encrypt-Hash (HEH) is a proposed block cipher mode of operation
which extends the strong pseudo-random permutation property of block
ciphers (e.g. AES) to arbitrary length input strings. This provides a
stronger notion of security than existing block cipher modes of
operation (e.g. CBC, CTR, XTS), though it is usually less performant.
It uses two keyed invertible hash functions with a layer of ECB
encryption applied in-between. The algorithm is currently specified by
the following Internet Draft:
https://tools.ietf.org/html/draft-cope-heh-01
This patch adds HEH as a symmetric cipher only. Support for HEH as an
AEAD is not yet implemented.
HEH will use an existing accelerated ecb(block_cipher) implementation
for the encrypt step if available. Accelerated versions of the hash
step are planned but will be left for later patches.
This patch backports HEH to the 4.4 Android kernel, initially for use by
ext4 filenames encryption. Note that HEH is not yet upstream; however,
patches have been made available on linux-crypto, and as noted there is
also a draft specification available. This backport required updating
the code to conform to the legacy ablkcipher API rather than the
skcipher API, which wasn't complete in 4.4.
Signed-off-by: Alex Cope <alexcope@google.com>
Bug: 32975945
Signed-off-by: Eric Biggers <ebiggers@google.com>
Change-Id: I945bcc9c0115916824d701bae91b86e3f059a1a9
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