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The resource key hash is a mechanism allowing Google to verify the integrity of the wrapped encryption keys without having access to the keys.
Generating the resource key hash requires access to the unwrapped key including the DEK, the resource_name and the perimeter_id specified during the key wrapping operation.
We use the cryptographic function HMAC-SHA256 with unwrapped_dek as a key and the concatenation of metadata as data ("ResourceKeyDigest:", resource_name, ":", perimeter_id). The resource_name and perimeter_id should be UTF-8 encoded strings.
For example, when resource_name = "my_resource", perimeter_id = "my_perimeter" and unwrapped_dek = 0xf00d, the resource key hash is:
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2024-11-14 UTC."],[],["The core mechanism is generating a resource key hash to verify wrapped encryption key integrity. This involves using HMAC-SHA256 with the unwrapped DEK as the key and a specific concatenation of metadata as data. The metadata consists of \"ResourceKeyDigest:\", the UTF-8 encoded `resource_name`, \":\", and the UTF-8 encoded `perimeter_id`. An example shows generating the hash using `openssl` with a sample `resource_name`, `perimeter_id`, and `unwrapped_dek`.\n"]]
