From 4e4ff5da9850ff3fb1876ceea72ded30d2bbf20d Mon Sep 17 00:00:00 2001 From: Andreas Naive Date: Fri, 17 Jun 2011 23:34:53 +0000 Subject: [PATCH] removed some obsolete commentaries. Not worth. --- src/mame/machine/naomibd.c | 17 ++--------------- 1 file changed, 2 insertions(+), 15 deletions(-) diff --git a/src/mame/machine/naomibd.c b/src/mame/machine/naomibd.c index 992d7ed3bbe..250cdb6a972 100644 --- a/src/mame/machine/naomibd.c +++ b/src/mame/machine/naomibd.c @@ -1436,7 +1436,7 @@ M1: DMA read of protected ROM area M2: special read of ROM area which supplies decryption key first M3: normal read followed by write to cart's decryption buffer (up to 64kB), followed by M2 but from buffer area -M1's working is still unclear (more on this later), so we will be speaking of M2 & M3 most of the time. +Notes below refer to M2 & M3. The encryption is done by a stream cipher operating in counter mode, which use a 16-bits internal block cipher. @@ -1454,7 +1454,7 @@ internal block-cipher. So, at a given step, the internal block cipher will outpu given plaintext word, and the remaining 2 to the next plaintext word. The underlying block cipher consists of two 4-round Feistel Networks (FN): the first one takes the counter (16 bits), -the game-key (>=25 bits) and the sequence-key (16 bits) and output a middle result (16 bits) which will act as another key +the game-key (>=26 bits) and the sequence-key (16 bits) and output a middle result (16 bits) which will act as another key for the second one. The second FN will take the encrypted word (16 bits), the game-key, the sequence-key and the result from the first FN and will output the decrypted word (16 bits). @@ -1484,19 +1484,6 @@ It can be observed that a couple of sboxes have incomplete tables (a 255 value i as of december/2010 show small randomness and big correlations, making possible that some unseen bits could make the decryption need those incomplete parts. -When bit #1 of the heading control bits is set to 1, an additional decompression step seems to be carried out. As of -february/2010, Deunan Knute has put some work on analyzing the decompression algorithm, but probably much more work will -be needed to completely reverse engineer it. Interested devs with quick access to hardware tests are welcomed to join -the task. - -Guilty Gear X & Sega Tetris are examples of games using the decompression ingame. - -Due to technical details, it's more difficult to get custom decryption data from M1 carts, which hinders some types of -analysis. The only M1 cart which have received attention until now have been AH! MY GODDESS. The available data clearly -doesn't have the same structure than M2&M3 carts using only the decryption step. However, due to that some hardware tests -show cycled structures similar to the ones returned by M2&M3 carts using the decompression algo, it's conjectured that M1 -carts will be using the same decompression algorithm seen in M2&M3 ones. - ****************************************************************************************/ struct sbox