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Add one-by-one measurement report format.
Rename existing one to Standard All-Measurements Report Definition. Signed-off-by: Jiewen Yao <[email protected]>
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‎doc/standard_measurement_report.md‎

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@@ -13,9 +13,12 @@ SPDM Requester and consumed by a Verifier while all agents are operating in prod
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particular, a production Verifier may only support a measurement report of this type and can point
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to this document to advertise that restriction to other agents.
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## Standard Measurement Report Definition
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There are 2 types of Standard Measurement Report. A verifier should support All-Measurements Report
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and may support One-by-One-Measurements Report.
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The standard measurement report is a byte buffer that consists of the L1/L2 transcript along with
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## Standard All-Measurements Report Definition
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The standard all-measurements report is a byte buffer that consists of the L1/L2 transcript along with
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the signature over the transcript if the Responder supports signing. It is comprised of a single
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`GET_MEASUREMENTS` request and a single `MEASUREMENTS` response.
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* For SPDM 1.3 and later, `NewMeasurementRequested` is not set.
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* This requests the current state of the Responder and not its future state.
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## Standard One-by-One-Measurements Report Definition
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The standard one-by-one-measurements report is a byte buffer that consists of the L1/L2 transcript along with
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the signature over the transcript if the Responder supports signing. It is comprised of multiple
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`GET_MEASUREMENTS` requests and multiple `MEASUREMENTS` responses.
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For SPDM 1.0 and 1.1, the byte buffer is {`GET_MEASUREMENTS`(0), `MEASUREMENTS`(0),
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`GET_MEASUREMENTS`(1), `MEASUREMENTS`(1), ..., `GET_MEASUREMENTS`(n), `MEASUREMENTS`(n)}.
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For SPDM 1.2 and later, the byte buffer is {`VCA`, `GET_MEASUREMENTS`(0), `MEASUREMENTS`(0),
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`GET_MEASUREMENTS`(1), `MEASUREMENTS`(1), ..., `GET_MEASUREMENTS`(n), `MEASUREMENTS`(n)}.
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The `GET_MEASUREMENTS`(0) request has the following properties:
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* `Param2 = 0x00`
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* Total number of measurement blocks is requested.
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* Assuming that the Responder returns `n` measurement blocks in `MEASUREMENTS`(0).
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* `SignatureRequested` is not set.
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* For SPDM 1.2 and later, `RawBitStreamRequested` is not set.
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* For SPDM 1.3 and later, `NewMeasurementRequested` is not set.
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The `GET_MEASUREMENTS`(1) to `GET_MEASUREMENTS`(n) request has the following properties:
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* `Param2`
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* The requested measurement index. It should be between 0x1 and 0xFE, inclusive and incremental.
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* Only successful `GET_MEASUREMENTS`(x) and `MEASUREMENTS`(x) are recorded in the measurement report.
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* `SignatureRequested`
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* For `GET_MEASUREMENTS`(1), ..., and `GET_MEASUREMENTS`(n-1), it is not set.
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* For `GET_MEASUREMENTS`(n), if the Responder supports signature generation (`MEAS_CAP = 10b`)
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then it is set, else it is not set.
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* For SPDM 1.2 and later, if the requester detected the signed `MEASUREMENT`(n)
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`content change` field is `01b`(changed), the requester should discard this measurement report
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and recollect from the beginning.
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* For SPDM 1.2 and later, `RawBitStreamRequested` is not set.
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* For SPDM 1.3 and later, `NewMeasurementRequested` is not set.
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## Rationale
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### Single Request and Response
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### Single or One-by-One Request and Response
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Capturing all measurements in a single response provides an atomic snapshot of the state of the
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Responder at a specific point in time. As such, a Verifier need not have to reason about the state
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of the Responder through multiple measurement requests and responses with a possibly unknown amount
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of time between each message.
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The requester should collect All-Measurements Report at first. Only if the device cannot return
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all measurements at one time due to some errors (such as transport layer limitation),
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then the requester can try to collect One-by-One-Measurements Report.
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### Detecting Measurement Report format
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The verifier may check the first `GET_MEASUREMENTS` in the Measurement Report.
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* If the `Param2` is `0xFF`(All Measurements), then it is All-Measurements Report.
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The whole Measurement report should include only one `GET_MEASUREMENTS`/`MEASUREMENTS` pair.
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* If the `Param2` is `0x00`(Total Number), then it is One-by-One-Measurements Report.
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The whole Measurement report should include only `n`+1 `GET_MEASUREMENTS`/`MEASUREMENTS` pairs.
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### Byte Buffer
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A raw byte buffer allows the Verifier to verify the signature, if supported by the Responder, over
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Presumably the Verifier evaluates the current state of the Responder and not its future state. As
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such `NewMeasurementRequested` is not set.
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### Non-Sequentially Increased Measurement Index
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If One-by-One-Measurements report is used, the `Param2`(measurement index) in `GET_MEASUREMENTS`(1)
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to `GET_MEASUREMENTS`(n) is non-sequentially incremental.
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A device may implement non-sequentially increased measurement index.
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For example, a device has 3 measurement blocks. The index is 1, 4 and 6.
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Then the `Param2` of `GET_MEASUREMENTS`(1) is 1, the `Param2` of `GET_MEASUREMENTS`(2) is 4,
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and the `Param2` of `GET_MEASUREMENTS`(3) is 6.
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The requester may send a `GET_MEASUREMENTS` with `Param2` 2, but it will get `ERROR` response.
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As such, the `GET_MEASUREMENTS` with `Param2` 2 and `ERROR` response are NOT included
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in the measurement report.
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Once the successfully received number of measurement block is `n`-1, the requester should send
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the next `GET_MEASUREMENTS` with `SignatureRequested` set.
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### Completeness
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All-Measurements report includes all measurements. The compleness is guaranteed.
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If One-by-One-Measurements report is used,
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the requester should request the total number of measurement block (`n`) first,
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then request all `n` measurement blocks one by one incrementally.
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### Atomicity
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All-Measurements report is a snapshot for the device state. The atomicity is guaranteed.
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If One-by-One-Measurements report is used,
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the requester should verify the `content change` and recollect One-by-One-Measurements report
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in case that the `MeasurementRecord` fields of previous `MEASUREMENTS` responses are changed.
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### Freshness
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The verifier should input a nonce value and check the nonce value in the measurement report
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to ensure the freshness of the measurement report, if digital signature is supported.
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### Integrity
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The verifier should request a digital signature in the last message `GET_MEASUREMENTS`
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for the whole measurement report, if supported by the Responder.
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### Device Identity
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The verifier should verify the device identity at first (e.g. certificate or raw public key),
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then verify the digital signature of the measurement report.
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