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--- atracdownload-wiki [2010/06/08 09:10] – megadiscman
+++ atracdownload-wiki [2011/08/10 22:04] (current) – alex
@@ Line 1: / Line 1: @@
-This document is based on [[atracdownload]] from the FreeMD repository
+This document is based on [[atracdownload]] from the FreeMD repository. Also compare http://bertrik.sikken.nl/netmd/download.html
 ====== Downloading an ATRAC track to a NetMD unit ======
@@ Line 25: / Line 25: @@
-==== 1. UNKNOWN PURPOSE ====
+==== 1. DISABLE TRACK PROTECTION FOR NEXT SESSION ====
   => 00 18 00 08 00 46 f0 03 01 03  2b ff 00 01 00 00 01
   <= 09 18 00 08 00 46 f0 03 01 03  2b 00 00 01 00 00 01
+This instruction tells the MD unit to not set the "protected" bit for following downloaded tracks. It is effective until reset with the same instruction, but having the last byte 00, or the end of the current session.
 ==== 2. START AUTHENTICATED SESSION ====
-  => 00 18 00 08 00 46 f0 03 01 03  80 ff 00 00 00 00 00
+  => 00 18 00 08 00 46 f0 03 01 03  80 ff
-  <= 09 18 00 08 00 46 f0 03 01 03  80 00 00 00 00 00 00
+  <= 09 18 00 08 00 46 f0 03 01 03  80 00
 NOTE: You hear head movement (disc spinning up).
@@ Line 41: / Line 42: @@
 ==== 3.  REQUEST FOR LEAF ID ====
-  => 00 18 00 08 00 46 f0 03 01 03  11 ff 00 00 00 00 00
+  => 00 18 00 08 00 46 f0 03 01 03  11 ff
   <= 09 18 00 08 00 46 f0 03 01 03  11 00 01 00 00 21 cf 06 00 00
@@ Line 101: / Line 102: @@
      $m(1) ... $m(8)
   <= 09 18 00 08 00 46 f0 03 01 03 20 00 00 00 00
-     !m(1) ... !m(1)
+     !m(1) ... !m(8)
-$m is a nonce from the host and !m is a nonce from the device. These two 8-byte-values are used to create a 16-byte 3DES key.
+$m is a nonce from the host and !m is a nonce from the device. These two 8-byte-values are concatenated to form a 16-byte value. The Retail MAC without padding of that value, using the root key of the EKB transferred as key for the MAC will be the session key.
-==== 6. TRANSFER ENCRYPTED CONTENT KEY ? ====
+For "Retail MAC" aka "CBC-MAC-Y" aka "ISO/IEC 9797-1, algorithm 3" see google. It basically is standard DES CBC-MAC for all but the last blocks, while the last block is encrypted using 3DES-CBC. The initial IV is zero.
+==== 6. TRANSFER CONTENT ID AND ENCRYPTION KEY ====
   => 00 18 00 08 00 46 f0 03 01 03 22 ff 00 00
      $m(1) ... $m(32)
   <= 00 18 00 08 00 46 f0 03 01 03 22 00 00 00
+$m(1) ... $m(32) is DES encrypted using the session key negotiated in the previous step. The corresponding plain text is
+01 01 01 $c(1) ... $c(20) $k(1) ... $k(8)
+where $c(1) ... $c(20) is the Content ID of the track to transfer (a kind of UUID to recognize the copyrighted work) and $k(1) ... $k(8) is the Key Encryption Key.
 ==== 7. TRANSFER TRACK DATA ====
@@ Line 119: / Line 128: @@
 ffff is a placeholder for the track number (indicated by 10 01).
-$p$q is the format, 0006 for SP, 9402 for LP2 and a800 for LP4.  $r$s
+$p$q is the format, 0006 for SP, 9402 for LP2 and a800 for LP4.  $r$s for LP2 and LP4 is the number of frames (of 96 bytes for LP4 or 192 bytes for LP2); $t$u$v$w is the number of bytes transferred through the bulk pipe. The number includes the packing overhead.
-is an unknown value proportional to the file size.  $t$u$v$w is the
-size of bytes transfered.
+The meaning or $r$s for SP is not yet known.
 The player returns __twice__ from this command.  First it just echoes it
@@ Line 132: / Line 141: @@
   <= 09 18 00 08 00 46 f0 03 01 03 28 ff 00 01
 10 01 00 !t 00 $p $q 00 00 $r $s $t $u $v $w
+     $m(0) ... $m(32)
 The track number of the recorded track is returned in !t.
-NOTE: We don't know how $p$w is calculated.
+$m(x) is DES CBC encrypted by the session key (IV zero), and after decryption contains the concatenation of
+  - An 8 byte value identifying the track (needed on check-in to verify which copyrighted work will be deleted and adjust the check-out counter)
+  - Four padding bytes (seen as 00 00 00 00 or 01 01 01 01)
+  - The 20-byte Content ID
 NOTE: The data is split into blocks of 3f00 bytes each (except the
 last one), and each one has a header:
-00 00 00 00 00 $u $v $m(1) ... $m(8)
+00 00 00 00 00 $u $v $k(1) ... $k(8) $i(1) ... $i(8)
-where $u$v is the block size (usually 3f00) and $m(x) is unknown
+where $u$v is the block size (usually 3f00), $k(x) is the key for DES CBC encryption of the data in this block, and $i(x) is the IV for the DES CBC encryption. The key itself is DES **decrypted** by the key encryption key, i.e. you have to **encrypt** it to get the plain key.
-(possibly a key).
-This means for the total nr of bytes: len + (len/3f00)*16 + 16
+This means for the total nr of bytes: len + ((len+0x3eff)/3f00)*24
 ==== 8. TOC Edit ====
@@ Line 164: / Line 176: @@
 01 00 $t
-$t is the track number.  $m(x) is possibly some Integrity Check Value.
+$t is the track number.  $m(x) is a simple authorization value: It's 0000000000000000 DES encrypted by the session key.
 ==== 10. FORGET SESSION KEY ====
@@ Line 173: / Line 185: @@
 ==== 11. END AUTHENTICATED SESSION ====
-  => 00 18 00 08 00 46 f0 03 01 03 81 ff 00 00 00
+  => 00 18 00 08 00 46 f0 03 01 03 81 ff
-  <= 09 18 00 08 00 46 f0 03 01 03 81 00 00 00 00
+  <= 09 18 00 08 00 46 f0 03 01 03 81 00