IMG3 File Format

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Revision as of 03:04, 10 August 2008 by Cool name (talk | contribs)
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This is the replacement for the IMG2 File Format in 2.0 firmware.

Header

struct Img3 {
 unsigned int magic;
 unsigned int dataLenPad;
 unsigned int u1; // offSet to 20 byte footer
 unsigned int certOffset;
 unsigned int name;
 unsigned int type;
 unsigned int nameOffset;
 unsigned int dataLen;
} typedef Img3;

Tag Format

unsigned int magic;
unsigned int total_length;   //data_length+0xC
unsigned int data_length;

Tags

VERS: Version
SEPO: Unknown
BORD: Board to be used with
KBAG: contains the KEY and IV required to decrypt encrypted with the GID-key
SHSH: RSA encrypted SHA1 hash of the file
CERT: Certificate

Encryption

Apple got smarter this time, requiring the Hardware AES engine to be run per file. Decrypt the KBAG tag data (0x20 bytes?) with the hardware AES engine and get the 0x10 byte IV and the 0x10 byte KEY.

Resources

cmw's IMG3 Unpacker