Make session transcript more flexible (#74)

* Make SessionTranscript more flexible.

Makes SessionTranscript more flexible so that other transport
protocols can reuse the core components of this library.

Also remove the old OpenID4VP code.

* Use generics

* Remove oid4vp-specific definitions

src/definitions/device_signed.rs

@@ -4,7 +4,7 @@ use crate::definitions::{
 };
 use cose_rs::sign1::CoseSign1;
 use serde::{Deserialize, Serialize};
-use serde_cbor::Value as CborValue;
+use serde_cbor::{Error as CborError, Value as CborValue};
 use std::collections::BTreeMap;
 
 #[derive(Clone, Debug, Deserialize, Serialize)]
@@ -28,22 +28,19 @@ pub enum DeviceAuth {
     Mac { device_mac: CborValue },
 }
 
-pub type DeviceAuthenticationBytes = Tag24<DeviceAuthentication>;
+pub type DeviceAuthenticationBytes<S> = Tag24<DeviceAuthentication<S>>;
 
 #[derive(Clone, Debug, Deserialize, Serialize)]
-pub struct DeviceAuthentication(
+pub struct DeviceAuthentication<S: SessionTranscript>(
     &'static str,
-    pub SessionTranscript,
-    pub String,
-    pub DeviceNamespacesBytes,
+    // See https://github.com/serde-rs/serde/issues/1296.
+    #[serde(bound = "")] S,
+    String,
+    DeviceNamespacesBytes,
 );
 
-impl DeviceAuthentication {
-    pub fn new(
-        transcript: SessionTranscript,
-        doc_type: String,
-        namespaces_bytes: DeviceNamespacesBytes,
-    ) -> Self {
+impl<S: SessionTranscript> DeviceAuthentication<S> {
+    pub fn new(transcript: S, doc_type: String, namespaces_bytes: DeviceNamespacesBytes) -> Self {
         Self(
             "DeviceAuthentication",
             transcript,
@@ -52,3 +49,9 @@ impl DeviceAuthentication {
         )
     }
 }
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("Unable to encode value as CBOR: {0}")]
+    UnableToEncode(CborError),
+}

src/definitions/mod.rs

@@ -7,7 +7,6 @@ pub mod helpers;
 pub mod issuer_signed;
 pub mod mso;
 pub mod namespaces;
-pub mod oid4vp;
 pub mod session;
 pub mod traits;
 pub mod validity_info;
@@ -22,5 +21,5 @@ pub use device_response::{DeviceResponse, Document};
 pub use device_signed::{DeviceAuth, DeviceSigned};
 pub use issuer_signed::{IssuerSigned, IssuerSignedItem};
 pub use mso::{DigestAlgorithm, DigestId, DigestIds, Mso};
-pub use session::{SessionData, SessionEstablishment, SessionTranscript};
+pub use session::{SessionData, SessionEstablishment, SessionTranscript180135};
 pub use validity_info::ValidityInfo;

src/definitions/session.rs

@@ -29,7 +29,7 @@ use sha2::{Digest, Sha256};
 pub type EReaderKey = CoseKey;
 pub type EDeviceKey = CoseKey;
 pub type DeviceEngagementBytes = Tag24<DeviceEngagement>;
-pub type SessionTranscriptBytes = Tag24<SessionTranscript>;
+pub type SessionTranscriptBytes = Tag24<SessionTranscript180135>;
 pub type NfcHandover = (ByteStr, Option<ByteStr>);
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -78,13 +78,17 @@ impl TryFrom<u64> for Status {
     }
 }
 
+pub trait SessionTranscript: Serialize + for<'a> Deserialize<'a> {}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct SessionTranscript(
+pub struct SessionTranscript180135(
     pub DeviceEngagementBytes,
     pub Tag24<EReaderKey>,
     pub Handover,
 );
 
+impl SessionTranscript for SessionTranscript180135 {}
+
 #[derive(Debug, Clone, thiserror::Error)]
 pub enum Error {
     #[error("Curve not supported for DH exchange")]
@@ -164,7 +168,7 @@ pub fn get_shared_secret(
 
 pub fn derive_session_key(
     shared_secret: &SharedSecret<NistP256>,
-    session_transcript: &Tag24<SessionTranscript>,
+    session_transcript: &SessionTranscriptBytes,
     reader: bool,
 ) -> Result<GenericArray<u8, U32>> {
     let salt = Sha256::digest(serde_cbor::to_vec(session_transcript)?);
@@ -400,7 +404,7 @@ mod test {
         };
 
         let device_engagement_bytes = Tag24::new(device_engagement).unwrap();
-        let session_transcript = Tag24::new(SessionTranscript(
+        let session_transcript = Tag24::new(SessionTranscript180135(
             device_engagement_bytes,
             reader_key_bytes,
             Handover::QR,
@@ -456,7 +460,7 @@ mod test {
         assert_eq!(shared_secret_hex, SHARED_SECRET);
 
         let session_transcript_bytes = hex::decode(SESSION_TRANSCRIPT).unwrap();
-        let session_transcript: Tag24<SessionTranscript> =
+        let session_transcript: SessionTranscriptBytes =
             serde_cbor::from_slice(&session_transcript_bytes).unwrap();
 
         let session_key = derive_session_key(&shared_secret, &session_transcript, true).unwrap();

src/presentation/device.rs

@@ -10,21 +10,22 @@ use crate::{
         device_signed::{DeviceAuth, DeviceAuthentication, DeviceNamespacesBytes, DeviceSigned},
         helpers::{tag24, NonEmptyMap, NonEmptyVec, Tag24},
         issuer_signed::{IssuerSigned, IssuerSignedItemBytes},
-        session::{self, derive_session_key, get_shared_secret, Handover, SessionData},
-        CoseKey, DeviceEngagement, DeviceResponse, Mso, SessionEstablishment, SessionTranscript,
+        session::{
+            self, derive_session_key, get_shared_secret, Handover, SessionData, SessionTranscript,
+        },
+        CoseKey, DeviceEngagement, DeviceResponse, Mso, SessionEstablishment,
     },
     issuance::Mdoc,
 };
 use cose_rs::sign1::{CoseSign1, PreparedCoseSign1};
 use p256::FieldBytes;
 use serde::{Deserialize, Serialize};
 use serde_cbor::Value as CborValue;
+use session::SessionTranscript180135;
 use std::collections::BTreeMap;
 use std::num::ParseIntError;
 use uuid::Uuid;
 
-pub mod oid4vp;
-
 #[derive(Serialize, Deserialize)]
 pub struct SessionManagerInit {
     documents: Documents,
@@ -43,7 +44,7 @@ pub struct SessionManagerEngaged {
 #[derive(Serialize, Deserialize)]
 pub struct SessionManager {
     documents: Documents,
-    session_transcript: Tag24<SessionTranscript>,
+    session_transcript: SessionTranscript180135,
     sk_device: [u8; 32],
     device_message_counter: u32,
     sk_reader: [u8; 32],
@@ -168,20 +169,19 @@ impl SessionManagerEngaged {
         session_establishment: SessionEstablishment,
     ) -> anyhow::Result<(SessionManager, RequestedItems)> {
         let e_reader_key = session_establishment.e_reader_key;
-        let session_transcript = Tag24::new(SessionTranscript(
-            self.device_engagement,
-            e_reader_key.clone(),
-            self.handover,
-        ))
-        .map_err(Error::Tag24CborEncoding)?;
+        let session_transcript =
+            SessionTranscript180135(self.device_engagement, e_reader_key.clone(), self.handover);
+        let session_transcript_bytes =
+            Tag24::new(session_transcript.clone()).map_err(Error::Tag24CborEncoding)?;
 
         let e_device_key = p256::SecretKey::from_bytes(FieldBytes::from_slice(&self.e_device_key))?;
 
         let shared_secret = get_shared_secret(e_reader_key.into_inner(), &e_device_key.into())
             .map_err(Error::SharedSecretGeneration)?;
 
-        let sk_reader = derive_session_key(&shared_secret, &session_transcript, true)?.into();
-        let sk_device = derive_session_key(&shared_secret, &session_transcript, false)?.into();
+        let sk_reader = derive_session_key(&shared_secret, &session_transcript_bytes, true)?.into();
+        let sk_device =
+            derive_session_key(&shared_secret, &session_transcript_bytes, false)?.into();
 
         let mut sm = SessionManager {
             documents: self.documents,
@@ -418,8 +418,10 @@ impl PreparedDocument {
 }
 
 pub trait DeviceSession {
+    type ST: SessionTranscript;
+
     fn documents(&self) -> &Documents;
-    fn session_transcript(&self) -> &Tag24<SessionTranscript>;
+    fn session_transcript(&self) -> Self::ST;
     fn prepare_response(
         &self,
         requests: &RequestedItems,
@@ -516,7 +518,7 @@ pub trait DeviceSession {
                 }
             };
             let device_auth = DeviceAuthentication::new(
-                self.session_transcript().as_ref().clone(),
+                self.session_transcript(),
                 doc_type.clone(),
                 device_namespaces.clone(),
             );
@@ -579,12 +581,14 @@ pub trait DeviceSession {
 }
 
 impl DeviceSession for SessionManager {
+    type ST = SessionTranscript180135;
+
     fn documents(&self) -> &Documents {
         &self.documents
     }
 
-    fn session_transcript(&self) -> &Tag24<SessionTranscript> {
-        &self.session_transcript
+    fn session_transcript(&self) -> SessionTranscript180135 {
+        self.session_transcript.clone()
     }
 }