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update AVB signature layout in README.expert.md

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cfig 7 years ago
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README.expert.md
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@ -67,26 +67,79 @@
|<recovery dtbo> | recovery dtbo length |
|--------------------------------+-------------------------|
|<padding> | min(n * page_zie - len)|
+----------------------------------------------------------+
+----------------------------------------------------------+ --> end of data part
### 3. signature part
#### 3.1 Boot Image Signature (VBoot 1.0)
+--------------------------------+-------------------------+
+--------------------------------+-------------------------+ --> end of data part
|<signature> | signature length |
|--------------------------------+-------------------------|
|<padding> | defined by boot_signer |
+----------------------------------------------------------+
+--------------------------------+-------------------------+
#### 3.2 AVB Footer (VBoot 2.0)
item size in bytes position
+--------------------------------+-------------------------+ --> end of data part (say locaton A)
| VBMeta Header | total 256 |
| | |
| - Header Magic "AVB0" | 4 |
| - avb_version Major | 4 |
| - avb_version Minor | 4 |
| - authentication blob size | 8 |
| - auxiliary blob size | 8 |
| - algorithm type | 4 |
| - hash offset | 8 |
| - hash size | 8 |
| - signature offset | 8 |
| - signature size | 8 |
| - pub key offset | 8 |
| - pub key size | 8 |
| - pub key metadata offset | 8 |
| - pub key metadata size | 8 |
| - descriptors offset | 8 |
| - descriptors size | 8 |
| - rollback index | 8 |
| - flags | 4 |
| - RESERVED | 4 |
| - release string | 47 |
| - NULL | 1 |
| - RESERVED | 80 |
|--------------------------------+-------------------------+ --> (location A) + 256
| Authentication Blob | |
| - Hash of Header & Aux Blob | alg.hash_num_bytes |
| - Signature of Hash | alg.signature_num_bytes |
| - Padding | align by 64 |
+--------------------------------+-------------------------+
|<signature> | signature length |
|--------------------------------+-------------------------|
| ... | ... |
|<padding> | defined by avbtool, |
|<padding> | it will pad to requested|
|<padding> | image size |
| ... | ... |
+----------------------------------------------------------+
| Auxiliary Blob | |
| - descriptors | |
| - pub key | |
| - pub key meta data | |
| - padding | align by 64 |
+--------------------------------+-------------------------+
| Padding | align by block_size |
+--------------------------------+-------------------------+ --> (location A) + (block_size * n)
+--------------------------------+-------------------------+
| | |
| | |
| DONOT CARE CHUNK | |
| | |
| | |
+--------------------------------+-------------------------+
+--------------------------------+-------------------------+ --> partition_size - block_size
| Padding | block_size - 64 |
+--------------------------------+-------------------------+ --> partition_size - 64
| AVB Footer | total 64 |
| | |
| - Footer Magic "AVBf" | 4 |
| - Footer Major Version | 4 |
| - Footer Minor Version | 4 |
| - original image size | 8 |
| - VBMeta offset | 8 |
| - VBMeta size | 8 |
| - Padding | 28 |
+--------------------------------+-------------------------+ --> partition_size

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