I’m implementing server-side App Attest validation and trying to verify my implementation against Apple’s published Attestation Object Validation Guide sample. I have already filed Feedback Assistant report FB24281098. Using only the values published in Apple’s sample, I can reproduce four apparent inconsistencies: Nonce calculation The documented procedure says to compute: clientDataHash = SHA256(clientData) and then: nonce = SHA256(authenticatorData || clientDataHash) Using the published server challenge, this produces: 1d1ce78912897de88cfe9fce5521aab37abfb09dc544833ff115612552cf75f3 However, the nonce contained in the sample certificate / published expected nonce is: 87b7d06d93a4294e46f011e66b6cc400f0bab20729976c619580b42ae60bff6e That value is reproduced when the raw challenge is appended to authenticatorData instead of SHA256(challenge). The block labeled “Expected clientDataHash” also appears substantially longer than a 32-byte SHA-256 digest. Public-key hash / key ID SHA256 of the leaf certificate’s X9.62 uncompressed P-256 public key is: ce0498f58483fbb4da0d7b2c63a5a538f552d4adcb9a4fa916195c49613e655d This matches the decoded key ID / credential ID from the attestation object. However, the separately published expected public-key hash is: 8a71a32b625b68012102c6300a7b36cd3c990f3b09dce2b1dd0da79f193e9a46 which appears to be SHA256 of the key-ID bytes instead. Bundle version The sample certificate extension contains the value "1", while the guide prose describes "1.0". Validation category The sample extension contains four bytes 01 00 00 00, while the guide describes the value as UInt32 category 1. I’m looking for clarification on the authoritative wire representation / parsing rule. Could Apple please confirm the authoritative byte-level behavior for these four fields, particularly: whether the nonce must use SHA256(clientData) as documented; whether the key ID must equal SHA256 of the X9.62 uncompressed public key; the exact bundle-version comparison rule; and the canonical validation-category representation? I’m intentionally avoiding accepting multiple interpretations or adding fallback behavior in a security-sensitive server verifier, so clarification from Apple would be greatly appreciated.