DroidFS/app/libgocryptfs/gocryptfs_internal/eme

EME for Go

EME (ECB-Mix-ECB or, clearer, Encrypt-Mix-Encrypt) is a wide-block encryption mode developed by Halevi and Rogaway in 2003 [eme].

EME uses multiple invocations of a block cipher to construct a new cipher of bigger block size (in multiples of 16 bytes, up to 2048 bytes).

Quoting from the original [eme] paper:

We describe a block-cipher mode of operation, EME, that turns an n-bit block cipher into a tweakable enciphering scheme that acts on strings of mn bits, where m ∈ [1..n]. The mode is parallelizable, but as serial-efficient as the non-parallelizable mode CMC [6]. EME can be used to solve the disk-sector encryption problem. The algorithm entails two layers of ECB encryption and a “lightweight mixing” in between. We prove EME secure, in the reduction-based sense of modern cryptography.

Figure 2 from the [eme] paper shows an overview of the transformation:

This is an implementation of EME in Go, complete with test vectors from IEEE [p1619-2] and Halevi [eme-32-testvec].

It has no dependencies outside the standard library.

Is it patentend?

In 2007, the UC Davis has decided to abandon [patabandon] the patent application [patappl] for EME.

Related algorithms

EME-32 is EME with the cipher set to AES and the length set to 512. That is, EME-32 [eme-32-pdf] is a subset of EME.

EME2, also known as EME* [emestar], is an extended version of EME that has built-in handling for data that is not a multiple of 16 bytes long.
EME2 has been selected for standardization in IEEE P1619.2 [p1619.2].

References

[eme]

A Parallelizable Enciphering Mode
Shai Halevi, Phillip Rogaway, 28 Jul 2003
https://eprint.iacr.org/2003/147.pdf

Note: This is the original EME paper. EME is specified for an arbitrary number of block-cipher blocks. EME-32 is a concrete implementation of EME with a fixed length of 32 AES blocks.

[eme-32-email]

Re: EME-32-AES with editorial comments
Shai Halevi, 07 Jun 2005
http://grouper.ieee.org/groups/1619/email/msg00310.html

[eme-32-pdf]

Draft Standard for Tweakable Wide-block Encryption
Shai Halevi, 02 June 2005
http://grouper.ieee.org/groups/1619/email/pdf00020.pdf

Note: This is the latest version of the EME-32 draft that I could find. It includes test vectors and C source code.

[eme-32-testvec]

Re: Test vectors for LRW and EME
Shai Halevi, 16 Nov 2004
http://grouper.ieee.org/groups/1619/email/msg00218.html

[emestar]

EME*: extending EME to handle arbitrary-length messages with associated data
Shai Halevi, 27 May 2004
https://eprint.iacr.org/2004/125.pdf

[patabandon]

Re: [P1619-2] Non-awareness patent statement made by UC Davis
Mat Ball, 26 Nov 2007
http://grouper.ieee.org/groups/1619/email-2/msg00005.html

[patappl]

Block cipher mode of operation for constructing a wide-blocksize block cipher from a conventional block cipher
US patent application US20040131182
http://www.google.com/patents/US20040131182

[p1619-2]

IEEE P1619.2™/D9 Draft Standard for Wide-Block Encryption for Shared Storage Media
IEEE, Dec 2008
http://siswg.net/index2.php?option=com_docman&task=doc_view&gid=156&Itemid=41

Note: This is a draft version. The final version is not freely available and must be bought from IEEE.

Package Changelog

v1.1.1, 2020-04-13

• Update go vet call in test.bash to work on recent Go versions
• No code changes

v1.1, 2017-03-05

• Add eme.New() / *EMECipher convenience wrapper
• Improve panic message and parameter wording

v1.0, 2015-12-08

• Stable release