The 2.5 kernel gets crypto [LWN.net]

One of the first things Linus merged once he got back home was the brand new cryptographic API written by James Morris, David S. Miller, and Jean-François Dive, with ideas and code taken from many other places. This patch is interesting for a couple of reasons: it is a brand-new, previously unseen kernel crypto implementation, and it is the first time that serious cryptographic code has been included in the mainline kernel tree. With luck, worldwide crypto regulations will remain sane enough that this code can stay there.

This API's purpose is to provide fast, general-purpose cryptographic operations for the rest of the kernel. The driving need in the short term is IPSec (which has also been partially merged), but other applications, such as cryptographic filesystems, can also make use of this facility. Needless to say, use in the networking and filesystem layers places some strong performance demands on the cryptographic layer.

The new crypto API is based on the scatterlist structure, which is used in many other parts of the I/O subsystem. Scatterlists give direct access to the page structures describing the memory to be operated on, below the level of the virtual memory system. Among other things, this architecture means that data can be encrypted or decrypted "in place" in the buffers that are used for I/O operations. It should, in other words, be fast (if the crypto algorithms themselves are fast).

Three basic types of "transforms" are supported by this API: ciphers, digests, and compressors. The kernel currently has implementations for DES (including triple DES), MD4, MD5, and SHA. See Documentation/crypto/api-intro.txt for a quick overview of how this API works.

(As a postscript: a few people have asked if this API would be made available to user space. It would not be hard to write a system call or pseudo-device which would export this functionality, but it is hard to imagine why that would be useful. It would be better just to run the crypto algorithms in user space directly).

(Log in to post comments)

The 2.5 kernel gets crypto

Posted Oct 31, 2002 2:31 UTC (Thu) by kbob (guest, #1770) [Link]

The new crypto API is based on the scatterlist structure, which is used in many other parts of the I/O subsystem.

Using scatterlists also makes it easier to offload crypto functions to crypto hardware the way BSD does. I don't know whether anyone is talking about hardware assist, but it has to be in the back of some minds.

The 2.5 kernel gets crypto

Posted Nov 1, 2002 19:31 UTC (Fri) by leandro (guest, #1460) [Link]

> people have asked if this API would be made available to user space. It would not be hard to write a system call or pseudo-device which would export this functionality, but it is hard to imagine why that would be useful. It would be better just to run the crypto algorithms in user space directly

Simplicity. User space would be duplicate code with the one in the kernel. If people could use the code in the kernel, there would be less code to audit and optimize. There could be a penalty for context switching, but this could be an acceptable tradeoff.