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Difference between revisions of "IMG3 File Format"
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− | + | The '''IMG3''' file format was introduced with [[iOS|iPhone OS]] 2.0b4 to replace the broken [[S5L File Formats|IMG2 format]]. This format is used on all devices with an [[S5L8920]] or older; [[S5L8960|A7]] and newer devices use [[IM4P File Format|IM4P]] and [[IMG4 File Format|IMG4]] files. |
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− | == |
+ | ==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. |
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− | typedef struct Img3_t { |
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+ | |||
− | uint32_t magic; // ASCII_LITTLE_ENDIAN("Img3") |
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+ | 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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+ | |||
+ | == Contents == |
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+ | All numbers are stored in [[wikipedia:Endianness#Little-endian|little endian]] byte order; this includes the magic ''numbers'' (<code>magic</code> and <code>ident</code>). |
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+ | typedef struct img3File { |
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+ | uint32_t magic; // ASCII_LE("Img3") |
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uint32_t fullSize; // full size of fw image |
uint32_t fullSize; // full size of fw image |
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uint32_t sizeNoPack; // size of fw image without header |
uint32_t sizeNoPack; // size of fw image without header |
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// size of the start of the data section (the code) up to |
// size of the start of the data section (the code) up to |
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// the start of the RSA signature (SHSH section) |
// the start of the RSA signature (SHSH section) |
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− | uint32_t |
+ | uint32_t ident; // identifier of image, used when bootrom is parsing images |
// list to find LLB (illb), LLB parsing it to find iBoot (ibot), |
// list to find LLB (illb), LLB parsing it to find iBoot (ibot), |
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− | // etc. |
+ | // etc. |
+ | img3Tag tags[]; // continues until end of file |
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}; |
}; |
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+ | typedef struct img3Tag { |
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− | ==Tag Format== |
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+ | uint32_t magic; // [[#Tags|see below]] |
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− | typedef struct Img3Tag_t { |
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+ | uint32_t totalLength; // length of tag including "magic" and these two length values |
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− | uint32_t magic; |
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− | uint32_t |
+ | uint32_t dataLength; // length of tag data |
− | + | uint8_t data[dataLength]; |
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+ | uint8_t pad[totalLength - dataLength - 12]; // Typically padded to 4 byte multiple |
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}; |
}; |
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− | ==Tags== |
+ | == Tags == |
+ | Due to being written in little-endian byte order, these tags are actually backwards when written to the file (e.g. <code>VERS</code> is stored as <code>S R E V</code>). |
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− | [[VERS]]: iBoot version of the image |
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+ | [[VERS]]: [[iBoot]] version of the image |
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[[SEPO]]: Security Epoch |
[[SEPO]]: Security Epoch |
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[[SDOM]]: Security Domain |
[[SDOM]]: Security Domain |
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[[PROD]]: Production Mode |
[[PROD]]: Production Mode |
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− | [[CHIP]]: Chip to be used with. example: |
+ | [[CHIP]]: Chip to be used with. example: <code>0x8900</code> for [[S5L8900]]. |
[[BORD]]: Board to be used with |
[[BORD]]: Board to be used with |
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− | [[KBAG]]: |
+ | [[KBAG]]: Contains the IV and key required to decrypt; encrypted with the [[GID Key]] |
[[SHSH]]: RSA encrypted SHA1 hash of the file |
[[SHSH]]: RSA encrypted SHA1 hash of the file |
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[[CERT]]: Certificate |
[[CERT]]: Certificate |
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− | [[ECID]]: Exclusive Chip ID unique to every device |
+ | [[ECID]]: Exclusive Chip ID unique to every device |
− | [[TYPE]]: Type of image, should contain the same string as |
+ | [[TYPE]]: Type of image, should contain the same string as the header's <code>ident</code> |
[[DATA]]: Real content of the file |
[[DATA]]: Real content of the file |
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+ | [[Nonce|NONC]]: [[Nonce]] used when file was signed. |
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+ | [[CEPO]]: Chip epoch |
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+ | [[OVRD]]: |
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+ | [[RAND]]: |
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+ | [[SALT]]: |
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==Signature Check== |
==Signature Check== |
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Decryption is done using the modulus at cert + 0xA15 |
Decryption is done using the modulus at cert + 0xA15 |
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0xC to [[SHSH]] is SHAed |
0xC to [[SHSH]] is SHAed |
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− | |||
− | ==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 with the [[GID Key]] to get the key and IV, and use those to decrypt the [[DATA]] section of the firmware file. |
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− | |||
− | 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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[[Category:File Formats]] |
[[Category:File Formats]] |
Latest revision as of 18:35, 2 March 2023
The IMG3 file format was introduced with iPhone OS 2.0b4 to replace the broken IMG2 format. This format is used on all devices with an S5L8920 or older; A7 and newer devices use IM4P and IMG4 files.
Contents
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.
Contents
All numbers are stored in little endian byte order; this includes the magic numbers (magic
and ident
).
typedef struct img3File { uint32_t magic; // ASCII_LE("Img3") uint32_t fullSize; // full size of fw image uint32_t sizeNoPack; // size of fw image without header uint32_t 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) uint32_t ident; // identifier of image, used when bootrom is parsing images // list to find LLB (illb), LLB parsing it to find iBoot (ibot), // etc. img3Tag tags[]; // continues until end of file };
typedef struct img3Tag { uint32_t magic; // see below uint32_t totalLength; // length of tag including "magic" and these two length values uint32_t dataLength; // length of tag data uint8_t data[dataLength]; uint8_t pad[totalLength - dataLength - 12]; // Typically padded to 4 byte multiple };
Tags
Due to being written in little-endian byte order, these tags are actually backwards when written to the file (e.g. VERS
is stored as S R E V
).
VERS: iBoot version of the image 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 IV and key 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 TYPE: Type of image, should contain the same string as the header'sident
DATA: Real content of the file NONC: Nonce used when file was signed. CEPO: Chip epoch OVRD: RAND: SALT:
Signature Check
Decryption is done using the modulus at cert + 0xA15 0xC to SHSH is SHAed