Optional data is binary data placed in the PDI after the image header table (IHT). You can include your own optional data like data, version, and so on. For more information, refer to optionaldata.
This data is authenticated as part IHT Signature and IHT is added as additional authenticated data (AAD) for the first secure header (SH) of the image header (IH) during encryption along with IHT. This implies that the optional data content remains as plain text.
As part of Authentication Optimization, for partitions that use the same authentication keys, the partition hashes are placed as part of Optional Data. For more information, see Authentication Optimization.
This was added to support optional metadata that is always in clear text and is not considered Image or Partition information. This is located immediately after the IHT. The size of this data is determined by the Size of IHT Optional Data (offset 0x58) field in the IHT. The content is a list of the following data structure:
| Offset | Name | Description |
|---|---|---|
| 0x0 | ID |
The Data ID field identifies the type of data contained in the data structure. 0: None, can be used for padding 1: PLM Build Time configuration metadata as defined in the PLM Configuration document 2: Data structure version information used in In-Place PLM Update Compatibility Check 4: Reserved |
| 0x2 | Size |
Total optional data size in words The Size field specifies the number of words in the data structure. The minimal value is 1, indicating that no data or checksum is present . This is useful for padding. Value 2 indicates that checksum is present, but no data. |
| 0x4 | Data | Actual data including padding |
| Last | Checksum | Sum of all the previous words in this data structure |