DeviceAttestationSoftware

A DeviceAttestation for environments that do not support platform-backed attestations.

This format includes a key pair which reside on the device to be used for generating one or more DeviceAssertion. It doesn't actually prove anything - it can't - so this attestation type is normally used together with proving that the client possesses a secret. This proof is computed as follows

K = HKDF(
  ikm = secretUtf8Encoded,
  salt = challenge,
  info = "MpzAttestationWithSecret1",
  length = 32
)

proofOfSecret = HMAC(
  key = K,
  message = challenge || secretUtf8Encoded
)

using the server-provided challenge and SHA-256 as the hash function. This mechanism should be used carefully since in most cases embedding a secret in the client binary is inherently insecure due to the risk of attackers exfiltrating the secret.