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Difference between revisions of "IMG3 File Format"
ChronicDev (talk | contribs) |
ChronicDev (talk | contribs) |
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==Header== |
==Header== |
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struct Img3 { |
struct Img3 { |
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| − | + | u32 magic; // fourcc="IMG3" |
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| − | + | u32 fullSize; // full size of fw image |
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| − | + | u32 sizeNoPack; // size of fw image without header |
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| − | + | u32 sigCheckArea; // although that is just my name for it, this is the |
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| − | + | // size of the start of the data section (the code) up to |
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| − | + | // the start of the RSA signature (SHSH section) |
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| − | + | u32 iden; // identifier of image, used when bootrom is parsing images |
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| − | + | // list to find LLB (illb), LLB parsing it to find iBoot (ibot), |
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| − | + | // etc. |
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} typedef Img3; |
} typedef Img3; |
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==Tag Format== |
==Tag Format== |
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| − | + | u32 magic; |
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| − | + | u32 total_length; // data_length+0xC |
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| − | + | u32 data_length; |
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==Tags== |
==Tags== |
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VERS: Version |
VERS: Version |
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| − | SEPO: |
+ | [[SEPO]]: Security Epoch |
| + | [[SDOM]]: Security Domain |
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| − | PROD: Processor to be used with. |
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| + | [[PROD]]: Production Mode |
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| − | CHIP: Chip to be used with. "0x8900" for [[S5L8900]] and "0x8720" for [[S5L8720]]. Instead of there being a check against some piece of hardware, whatever is verifying this (bootrom / iBoot / LLB / etc.) has this hardcoded in. |
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| − | + | [[CHIP]]: Chip to be used with. example: "0x8900" for [[S5L8900]]. |
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| + | [[BORD]]: Board to be used with |
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[[KBAG]]: contains the KEY and IV required to decrypt encrypted with the [[GID-key]] |
[[KBAG]]: contains the KEY and IV required to decrypt encrypted with the [[GID-key]] |
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| − | SHSH: RSA encrypted SHA1 hash of the file |
+ | [[SHSH]]: RSA encrypted SHA1 hash of the file |
| − | CERT: Certificate |
+ | [[CERT]]: Certificate |
[[ECID]]: Exclusive Chip ID unique to every device with iPhone OS. |
[[ECID]]: Exclusive Chip ID unique to every device with iPhone OS. |
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==Encryption== |
==Encryption== |
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| − | Apple got smarter this time, requiring the Hardware AES engine to be run per file. Decrypt the [[KBAG]] tag data |
+ | Apple got smarter this time, requiring the Hardware AES engine to be run per file. Decrypt the [[KBAG]] tag data with the [[GID-key]] to get the key and IV, and use those to decrypt the [[DATA]] section of the firmware file. |
| − | + | In the current method, iBoot will always use the first 16 bytes of the [[KBAG]] as the IV, then the remaining 16 (aes-128, used with [[S5L8900]] and [[S5L8720]]), 24 (aes-192), or 32 (aes-256, used with [[S5L8920]]) bytes for the key. |
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==Resources== |
==Resources== |
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Revision as of 13:28, 7 August 2009
This is the replacement for the IMG2 File Format from firmware 2.0 and onward
Header
struct Img3 {
u32 magic; // fourcc="IMG3"
u32 fullSize; // full size of fw image
u32 sizeNoPack; // size of fw image without header
u32 sigCheckArea; // although that is just my name for it, this is the
// size of the start of the data section (the code) up to
// the start of the RSA signature (SHSH section)
u32 iden; // identifier of image, used when bootrom is parsing images
// list to find LLB (illb), LLB parsing it to find iBoot (ibot),
// etc.
} typedef Img3;
Tag Format
u32 magic; u32 total_length; // data_length+0xC u32 data_length;
Tags
VERS: Version SEPO: Security Epoch SDOM: Security Domain PROD: Production Mode CHIP: Chip to be used with. example: "0x8900" for S5L8900. 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 ECID: Exclusive Chip ID unique to every device with iPhone OS.
Signature Check
Decryption is done using the modulus at cert + 0xA15 0xC to HSHS is SHAed
Encryption
Apple got smarter this time, requiring the Hardware AES engine to be run per file. Decrypt the KBAG tag data with the GID-key to get the key and IV, and use those to decrypt the DATA section of the firmware file.
In the current method, iBoot will always use the first 16 bytes of the KBAG as the IV, then the remaining 16 (aes-128, used with S5L8900 and S5L8720), 24 (aes-192), or 32 (aes-256, used with S5L8920) bytes for the key.
