Hello Richard, On Sun, Jan 17, 2010 at 11:02:34PM +0100, Richard Zidlicky wrote: > > diff --git a/Documentation/crypto/lmk.txt b/Documentation/crypto/lmk.txt > > new file mode 100644 > > index 0000000..91ca7f7 > > --- /dev/null > > +++ b/Documentation/crypto/lmk.txt > > @@ -0,0 +1,102 @@ > > +Loop-AES compatible cipher block chaining modes > > +----------------------------------------------- > > + > > +The following table shows the Loop-AES name of the mode, the > > +Loop-AES version first supporting it, and the equivalent cipher > > +specification string for dm-crypt: > > + > > + single-key Loop-AES v1.x cbc-plain > > + multi-key-v2 Loop-AES v2.x lmk2-plain64-multi:64 > > + multi-key-v3 Loop-AES v3.x lmk3-plain64-multi:64 > > + > > +This text describes the multi-key-v2 and multi-key-v3 modes and > > +their implementation in the Linux kernel. > > pointer to alternative implementation with loop-AES? OK, I will point to Loop-AES itself. > > +The multi-key modes describe a combination of CBC using a > > +specific IV derivation function with the use of multiple > > +independent encryption keys. > > + > > +The IV derivation and block chaining are implemented as > > +blkciphers named "lmk2" and "lmk3". The support for multiple > > +encryption keys is implemented in dm-crypt. > > + > > +Multiple keys: > > + > > + Each sector is encrypted/decrypted with one of 64 independent > > + keys selected by the following rule: > > + > > + key = keys[sectornum % 64] > > + > > +IV derivation: > > + > > + IVs are derived from an MD5 digest of the sector number, parts > > + of the plaintext data and a mode specific format constant. The > > + multi-key-v3 mode additionally uses a 128-bit IV seed. > > + > > + v2IV = MD5(plaintext[16..511] || > > + le64(truncated-sector-number) || > > + le32(format-magic)) > > + > > + v3IV = MD5(ivseed || > > + plaintext[16..511] || > > + le64(truncated-sector-number) || > > + le32(format-magic)) > > ivseed = key_table[64] is nowhere declared. This is an implementation detail of Loop-AES, so I don't consider it belonging to the description of the modes here. Loop-AES v3 keyfiles contain 65 keys of which the last key is used as IV seed. > Also "||" should be explained, it is probably conatenation like in > Jari's description? Hard to think of a really intuitive notation.."o" > or "<<" might be intuitive for many but does not look too good in this > case, especially in ASCII. OK, I agree this needs pointing out. The "||" for concatenation is what I'm familiar with, I don't think I would understand "o" or "<<" as well. I will explain what it does. > > + The input IV supplied to lmk2 or lmk3 is expected to be the > > + sector number in 64-bit little endian as supplied by the > > + plain64 dm-crypt IV generator. It gets truncated to 56 bits > > + with the most significant byte set to 0x80: > > I believe preceding paragraoh can be completely omitted, is not easier to > understand than the pseudocode. OK. I'll drop the last sentence, the first one describing where the IV is expected to come from seems relevant. > > + truncated-sector-number = > > + (sectornum & 0x00ffffffffffffff) | 0x8000000000000000 > > would be better above the IV derivation descriptions. Noted. > > +Mode multi-key-v2 (lmk2-plain64-multi:64): > > + > > + key = keys[sectornum % 64] > > + > > + encrypt: > > + IV = MD5(plaintext[16..511] || > > + le64(truncated-sector-number) || > > + le32(format-magic)) > > no need to repeat the IV description here, could use the v2/v3IV in the pseudocode > bellow. I think repeating it makes it clearer which parts happen at which time, so I'd leave this as is. > For the decryption IVs it would be then better to use some more distinct > names because eg IV2 is fairly close to v2IV. Good point, thanks. Will change. > Btw did you send the other parts of the patch to the list? I did only > ever receive the description part so feel free to email me the other > parts. I did send them all to linux-crypto@vger. I'm not sure why you didn't receive them. I'll send you the missing parts and CC you on the next submission. Thanks again for your comments, Max - Linux-crypto: cryptography in and on the Linux system Archive: http://mail.nl.linux.org/linux-crypto/
