SPDM — Security & Attestation

Security Protocol and Data Model (DMTF DSP0274)

SPDM establishes trust between platform components. It answers: “Are you who you claim to be, and is your firmware intact?”

Key Capabilities

Capability	Purpose	Status
Authentication	Verify device identity via certificate chains	Implemented
Attestation	Report firmware measurements (integrity proof)	Implemented
Secure Sessions	Encrypted communication channels	Not yet implemented
CSR Generation	Request new certificates	Not yet implemented

Implementation Status

The spdm-lib is forked from Caliptra MCU and actively developed on the openprot branch.

Supported SPDM versions: 1.0, 1.1, 1.2, 1.3

Currently implemented: Responder only. The responder handles the core authentication flow:

Request	Response	Handler
`GET_VERSION`	`VERSION`	Version negotiation
`GET_CAPABILITIES`	`CAPABILITIES`	Feature discovery
`NEGOTIATE_ALGORITHMS`	`ALGORITHMS`	Algorithm selection
`GET_DIGESTS`	`DIGESTS`	Certificate chain hashes
`GET_CERTIFICATE`	`CERTIFICATE`	Certificate chain retrieval (chunked)
`CHALLENGE`	`CHALLENGE_AUTH`	Signed measurement proof
`GET_MEASUREMENTS`	`MEASUREMENTS`	Firmware measurement blocks
`CHUNK_GET`	`CHUNK_RESPONSE`	Large response chunking

Not yet implemented: Requester role, KEY_EXCHANGE, PSK_EXCHANGE, session-based messaging.

Cryptographic Algorithms

While the protocol layer defines support for many algorithms (RSA, ECDSA P-256/P-384/P-521, EdDSA, SHA-2/3, etc.), the current implementation is hardcoded to:

Signing: ECC P-384 (ECDSA)
Hashing: SHA-384

Post-quantum algorithm support is noted as a future extension.

Architecture

The library is #![no_std] (with extern crate alloc for async_trait). Key design:

Platform Abstraction Layer: Four async traits integrators must implement:
- SpdmTransport — send/receive over MCTP or other transport
- SpdmHash — hash operations (init/update/finalize)
- SpdmRng — random number generation
- SpdmEvidence — PCR quote retrieval for measurements
Zero-copy codec: zerocopy + bitfield crates for wire-format serialization
Transcript management: VCA buffer (256 bytes) + streaming M1/L1 hash contexts for signing
Certificate store: Up to 2 slots, async trait for chain reading, root hash, and signing
Measurements: Freeform manifest type with DMTF measurement specification support

Attestation Flow

sequenceDiagram
    participant V as Verifier
    participant P as PRoT (OpenPRoT)

    V->>P: GET_VERSION
    P-->>V: VERSION (1.0-1.3)

    V->>P: GET_CAPABILITIES
    P-->>V: CAPABILITIES

    V->>P: NEGOTIATE_ALGORITHMS
    P-->>V: ALGORITHMS (ECC P-384 + SHA-384)

    V->>P: GET_DIGESTS
    P-->>V: Certificate digests

    V->>P: GET_CERTIFICATE
    P-->>V: Certificate chain (chunked)

    V->>P: CHALLENGE
    P-->>V: Signed measurements

    Note over V: Verify signature & measurements
    Note over V: Trust decision made

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