From 90f75b88d86692ddbd2e5b52aa02b1e8215538d4 Mon Sep 17 00:00:00 2001
From: Nick Zana <me@nickzana.dev>
Date: Tue, 16 May 2023 16:05:57 -0400
Subject: [PATCH] fido-common: Implement Deserialize for
 attestation::CredentialData

Relies on ciborium as a dependency because coset requires one of
ciborium's error types. It should be possible to remove this type's
dependence on ciborium.
---
 crates/fido-common/Cargo.toml         |  3 +-
 crates/fido-common/src/attestation.rs | 57 ++++++++++++++++++++++++++-
 crates/fido-common/src/lib.rs         |  2 +
 3 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/crates/fido-common/Cargo.toml b/crates/fido-common/Cargo.toml
index aa96bd1..9981f22 100644
--- a/crates/fido-common/Cargo.toml
+++ b/crates/fido-common/Cargo.toml
@@ -6,8 +6,9 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+ciborium = { version = "0.2.1", default-features = false, optional = true }
 coset = { version = "0.3.4", default-features = false }
 serde = { version = "1", features = ["derive"], optional = true }
 
 [features]
-serde = ["dep:serde"]
+serde = ["dep:serde", "dep:ciborium"]
diff --git a/crates/fido-common/src/attestation.rs b/crates/fido-common/src/attestation.rs
index 58d3d15..5b76fe6 100644
--- a/crates/fido-common/src/attestation.rs
+++ b/crates/fido-common/src/attestation.rs
@@ -36,7 +36,7 @@ pub mod enterprise;
 /// > of registered `WebAuthn` Extensions is maintained in the IANA "WebAuthn
 /// > Attestation Statement Format Identifiers" registry
 /// > [IANA-WebAuthn-Registries] established by [RFC8809].
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum FormatIdentifier {
     /// > The "packed" attestation statement format is a WebAuthn-optimized
@@ -74,6 +74,7 @@ pub enum FormatIdentifier {
 /// > Attested credential data is a variable-length byte array added to the
 /// > authenticator data when generating an attestation object for a given
 /// > credential.
+#[derive(Debug)]
 pub struct CredentialData {
     /// > The AAGUID of the authenticator.
     pub aaguid: [u8; 16],
@@ -82,3 +83,57 @@ pub struct CredentialData {
     /// The public key of the credential.
     pub public_key: coset::CoseKey,
 }
+
+#[cfg(feature = "serde")]
+impl TryFrom<&[u8]> for CredentialData {
+    // TODO: Custom error type?
+    type Error = coset::CoseError;
+
+    fn try_from(data: &[u8]) -> Result<Self, Self::Error> {
+        // aaguid: 16 Bytes
+        // SAFETY: Validate that data.len >= 16 for aaguid bytes
+        if data.len() < 16 {
+            return Err(coset::CoseError::DecodeFailed(ciborium::de::Error::Io(
+                coset::EndOfFile,
+            )));
+        }
+        let (&aaguid, data) = data.split_array_ref::<16>();
+
+        // credentialIdLengh: 2 Bytes
+        // > Byte length L of credentialId, 16-bit unsigned big-endian integer. Value
+        // > MUST be ≤ 1023.
+        // SAFETY: Validate that there are 2 bytes for u16
+        if data.len() < 2 {
+            return Err(coset::CoseError::DecodeFailed(ciborium::de::Error::Io(
+                coset::EndOfFile,
+            )));
+        }
+        let (&credential_id_length, mut data) = data.split_array_ref::<2>();
+        let credential_id_length = u16::from_be_bytes(credential_id_length);
+        if credential_id_length > 1023 {
+            return Err(coset::CoseError::UnexpectedItem(
+                "a credentialIdLength (L) of greater than 1023",
+                "a 16-bit unsigned big-endian integer less than or equal to 1023",
+            ));
+        }
+
+        // credentialId: L (credential_id_length) Bytes
+        let credential_id: &[u8] = data.take(..credential_id_length as usize)
+            .ok_or(coset::CoseError::DecodeFailed(ciborium::de::Error::Io(
+                coset::EndOfFile,
+            )))?;
+
+        Ok(Self { aaguid, id: credential_id.to_vec(), public_key: Default::default() })
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'de> Deserialize<'de> for CredentialData {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de> {
+            let data = Vec::<u8>::deserialize(deserializer)?;
+            // TODO: Improve error handling
+            CredentialData::try_from(data.as_slice()).map_err(serde::de::Error::custom)
+    }
+}
diff --git a/crates/fido-common/src/lib.rs b/crates/fido-common/src/lib.rs
index 316066e..2bcce8d 100644
--- a/crates/fido-common/src/lib.rs
+++ b/crates/fido-common/src/lib.rs
@@ -1,3 +1,5 @@
+#![feature(split_array, slice_take)]
+
 pub mod attestation;
 pub mod authenticator;
 pub mod credential;