Implement generation-bound protocol cryptography

crates/lazaret-core/src/protocol/session.rs

@@ -0,0 +1,663 @@
+use std::collections::BTreeSet;
+use std::fmt;
+
+use ed25519_dalek::{SigningKey, VerifyingKey};
+use serde::Serialize;
+
+use crate::identity::{
+    CapabilityId, CertificateDigest, ProtocolCredentialId, RequestDigest, RequestId,
+    TrustManifestDigest,
+};
+use crate::records::{
+    DeveloperDecision, GenerationIdentity, MailboxCancellation, MailboxRequest, MailboxResult,
+    MailboxResultAck, MailboxResultChunk, ProtocolCredential, ProtocolCredentialRole,
+    ProtocolSubjectId, ProtocolVersion, SessionBinding, SessionRequestCapability, TlsCredential,
+    TlsRole, TlsSubjectId, TrustManifest,
+};
+
+use super::signing::{
+    ProtocolCodecError, ProtocolRecordKind, decode_signed, encode_payload, sha256, sign_payload,
+    trust_manifest_digest, verify_payload,
+};
+use super::window::MAX_UNACKNOWLEDGED_CHUNKS;
+use super::{MAX_RESULT_CHUNK_BYTES, request_digest};
+
+#[derive(Debug)]
+pub enum ProtocolValidationError {
+    Codec(ProtocolCodecError),
+    InvalidPublicKey,
+    ManifestDigestMismatch,
+    CertificateDigestMismatch,
+    CredentialDigestMismatch,
+    CapabilityDigestMismatch,
+    GenerationMismatch,
+    RoleMismatch,
+    SubjectMismatch,
+    SessionBindingMismatch,
+    CredentialMismatch,
+    CapabilityMismatch,
+    RequestMismatch,
+    RequestReplay,
+    ChunkTooLarge { length: usize },
+}
+
+impl fmt::Display for ProtocolValidationError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Codec(error) => error.fmt(formatter),
+            Self::InvalidPublicKey => formatter.write_str("protocol public key is invalid"),
+            Self::ManifestDigestMismatch => formatter.write_str("Trust Manifest digest mismatch"),
+            Self::CertificateDigestMismatch => {
+                formatter.write_str("TLS certificate digest mismatch")
+            }
+            Self::CredentialDigestMismatch => {
+                formatter.write_str("protocol credential digest mismatch")
+            }
+            Self::CapabilityDigestMismatch => {
+                formatter.write_str("Session Request Capability digest mismatch")
+            }
+            Self::GenerationMismatch => {
+                formatter.write_str("protocol generation identity mismatch")
+            }
+            Self::RoleMismatch => formatter.write_str("protocol credential role mismatch"),
+            Self::SubjectMismatch => formatter.write_str("protocol subject identity mismatch"),
+            Self::SessionBindingMismatch => formatter.write_str("session binding mismatch"),
+            Self::CredentialMismatch => formatter.write_str("protocol credential mismatch"),
+            Self::CapabilityMismatch => formatter.write_str("Session Request Capability mismatch"),
+            Self::RequestMismatch => formatter.write_str("escalation request correlation mismatch"),
+            Self::RequestReplay => {
+                formatter.write_str("escalation request ID was already admitted")
+            }
+            Self::ChunkTooLarge { length } => write!(
+                formatter,
+                "result chunk length {length} exceeds {MAX_RESULT_CHUNK_BYTES}"
+            ),
+        }
+    }
+}
+
+impl std::error::Error for ProtocolValidationError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Codec(error) => Some(error),
+            _ => None,
+        }
+    }
+}
+
+impl From<ProtocolCodecError> for ProtocolValidationError {
+    fn from(error: ProtocolCodecError) -> Self {
+        Self::Codec(error)
+    }
+}
+
+#[derive(Serialize)]
+struct TrustManifestClaims<'a> {
+    protocol_version: ProtocolVersion,
+    generation_identity: &'a GenerationIdentity,
+    tls_ca_sha256: CertificateDigest,
+    protocol_issuer_public_key: &'a [u8],
+}
+
+#[derive(Serialize)]
+struct ProtocolCredentialClaims<'a> {
+    protocol_version: ProtocolVersion,
+    generation_identity: &'a GenerationIdentity,
+    role: ProtocolCredentialRole,
+    subject_id: ProtocolSubjectId,
+    public_key: &'a [u8],
+}
+
+#[derive(Serialize)]
+struct SessionCapabilityClaims<'a> {
+    protocol_version: ProtocolVersion,
+    session_binding: &'a SessionBinding,
+    coordinator_credential_id: ProtocolCredentialId,
+    sandbox_credential_id: ProtocolCredentialId,
+}
+
+/// Creates a self-verifying manifest whose digest must still arrive through a trusted path.
+///
+/// # Errors
+///
+/// Returns an error when a claim cannot be encoded.
+pub fn issue_trust_manifest(
+    generation_identity: GenerationIdentity,
+    tls_ca_sha256: CertificateDigest,
+    protocol_issuer: &SigningKey,
+) -> Result<(TrustManifest, TrustManifestDigest), ProtocolValidationError> {
+    let public_key = protocol_issuer.verifying_key().to_bytes().to_vec();
+    let claims = TrustManifestClaims {
+        protocol_version: ProtocolVersion::V1,
+        generation_identity: &generation_identity,
+        tls_ca_sha256,
+        protocol_issuer_public_key: &public_key,
+    };
+    let claims = encode_payload(&claims)?;
+    let signature = sign_payload(ProtocolRecordKind::TrustManifest, &claims, protocol_issuer)?;
+    let manifest = TrustManifest {
+        protocol_version: ProtocolVersion::V1,
+        generation_identity,
+        tls_ca_sha256,
+        protocol_issuer_public_key: public_key,
+        issuer_signature: signature.to_vec(),
+    };
+    let encoded = encode_payload(&manifest)?;
+    let digest = trust_manifest_digest(&encoded);
+    Ok((manifest, digest))
+}
+
+/// Validates a pinned Trust Manifest and returns its protocol issuer key.
+///
+/// # Errors
+///
+/// Returns an error for a stale tuple, digest mismatch, malformed key, or invalid signature.
+pub fn verify_trust_manifest(
+    manifest: &TrustManifest,
+    trusted_digest: TrustManifestDigest,
+    expected_generation: &GenerationIdentity,
+    expected_tls_ca_sha256: CertificateDigest,
+) -> Result<VerifyingKey, ProtocolValidationError> {
+    if &manifest.generation_identity != expected_generation {
+        return Err(ProtocolValidationError::GenerationMismatch);
+    }
+    if manifest.tls_ca_sha256 != expected_tls_ca_sha256 {
+        return Err(ProtocolValidationError::CertificateDigestMismatch);
+    }
+    let encoded = encode_payload(manifest)?;
+    if trust_manifest_digest(&encoded) != trusted_digest {
+        return Err(ProtocolValidationError::ManifestDigestMismatch);
+    }
+    let key_bytes: [u8; 32] = manifest
+        .protocol_issuer_public_key
+        .as_slice()
+        .try_into()
+        .map_err(|_| ProtocolValidationError::InvalidPublicKey)?;
+    let key = VerifyingKey::from_bytes(&key_bytes)
+        .map_err(|_| ProtocolValidationError::InvalidPublicKey)?;
+    let claims = TrustManifestClaims {
+        protocol_version: manifest.protocol_version,
+        generation_identity: &manifest.generation_identity,
+        tls_ca_sha256: manifest.tls_ca_sha256,
+        protocol_issuer_public_key: &manifest.protocol_issuer_public_key,
+    };
+    verify_payload(
+        ProtocolRecordKind::TrustManifest,
+        &encode_payload(&claims)?,
+        &manifest.issuer_signature,
+        &key,
+    )?;
+    Ok(key)
+}
+
+/// Issues one generation- and role-bound protocol credential.
+///
+/// # Errors
+///
+/// Returns an error when a claim cannot be encoded.
+pub fn issue_protocol_credential(
+    generation_identity: GenerationIdentity,
+    role: ProtocolCredentialRole,
+    subject_id: ProtocolSubjectId,
+    subject_key: &VerifyingKey,
+    protocol_issuer: &SigningKey,
+) -> Result<ProtocolCredential, ProtocolValidationError> {
+    let public_key = subject_key.to_bytes().to_vec();
+    let claims = ProtocolCredentialClaims {
+        protocol_version: ProtocolVersion::V1,
+        generation_identity: &generation_identity,
+        role,
+        subject_id,
+        public_key: &public_key,
+    };
+    let claims = encode_payload(&claims)?;
+    let credential_id = ProtocolCredentialId::new(sha256(&claims));
+    let signature = sign_payload(
+        ProtocolRecordKind::ProtocolCredential,
+        &claims,
+        protocol_issuer,
+    )?;
+    let credential = match (role, subject_id) {
+        (
+            ProtocolCredentialRole::SessionCoordinator,
+            ProtocolSubjectId::SessionCoordinator(subject_id),
+        ) => ProtocolCredential::session_coordinator(
+            credential_id,
+            generation_identity,
+            subject_id,
+            public_key,
+            signature.to_vec(),
+        ),
+        (ProtocolCredentialRole::AgentSandbox, ProtocolSubjectId::AgentSandbox(subject_id)) => {
+            ProtocolCredential::agent_sandbox(
+                credential_id,
+                generation_identity,
+                subject_id,
+                public_key,
+                signature.to_vec(),
+            )
+        }
+        _ => return Err(ProtocolValidationError::RoleMismatch),
+    };
+    Ok(credential)
+}
+
+/// Validates one protocol credential against its issuer and exact authority tuple.
+///
+/// # Errors
+///
+/// Returns an error for key, role, subject, generation, digest, or signature mismatch.
+pub fn verify_protocol_credential(
+    credential: &ProtocolCredential,
+    protocol_issuer: &VerifyingKey,
+    expected_generation: &GenerationIdentity,
+    expected_role: ProtocolCredentialRole,
+    expected_subject: ProtocolSubjectId,
+) -> Result<VerifyingKey, ProtocolValidationError> {
+    if &credential.generation_identity != expected_generation {
+        return Err(ProtocolValidationError::GenerationMismatch);
+    }
+    if credential.role() != expected_role {
+        return Err(ProtocolValidationError::RoleMismatch);
+    }
+    if credential.subject_id() != expected_subject {
+        return Err(ProtocolValidationError::SubjectMismatch);
+    }
+    let claims = ProtocolCredentialClaims {
+        protocol_version: credential.protocol_version,
+        generation_identity: &credential.generation_identity,
+        role: credential.role(),
+        subject_id: credential.subject_id(),
+        public_key: &credential.public_key,
+    };
+    let claims = encode_payload(&claims)?;
+    if credential.credential_id != ProtocolCredentialId::new(sha256(&claims)) {
+        return Err(ProtocolValidationError::CredentialDigestMismatch);
+    }
+    verify_payload(
+        ProtocolRecordKind::ProtocolCredential,
+        &claims,
+        &credential.issuer_signature,
+        protocol_issuer,
+    )?;
+    let key_bytes: [u8; 32] = credential
+        .public_key
+        .as_slice()
+        .try_into()
+        .map_err(|_| ProtocolValidationError::InvalidPublicKey)?;
+    VerifyingKey::from_bytes(&key_bytes).map_err(|_| ProtocolValidationError::InvalidPublicKey)
+}
+
+/// Issues one capability for an exact live session and credential pair.
+///
+/// # Errors
+///
+/// Returns an error when its claims cannot be encoded.
+pub fn issue_session_capability(
+    session_binding: SessionBinding,
+    coordinator_credential_id: ProtocolCredentialId,
+    sandbox_credential_id: ProtocolCredentialId,
+    coordinator_key: &SigningKey,
+) -> Result<SessionRequestCapability, ProtocolValidationError> {
+    let claims = SessionCapabilityClaims {
+        protocol_version: ProtocolVersion::V1,
+        session_binding: &session_binding,
+        coordinator_credential_id,
+        sandbox_credential_id,
+    };
+    let claims = encode_payload(&claims)?;
+    let capability_id = CapabilityId::new(sha256(&claims));
+    let signature = sign_payload(
+        ProtocolRecordKind::SessionRequestCapability,
+        &claims,
+        coordinator_key,
+    )?;
+    Ok(SessionRequestCapability {
+        protocol_version: ProtocolVersion::V1,
+        capability_id,
+        session_binding,
+        coordinator_credential_id,
+        sandbox_credential_id,
+        coordinator_signature: signature.to_vec(),
+    })
+}
+
+fn verify_session_capability(
+    capability: &SessionRequestCapability,
+    session_binding: &SessionBinding,
+    coordinator_credential_id: ProtocolCredentialId,
+    sandbox_credential_id: ProtocolCredentialId,
+    coordinator_key: &VerifyingKey,
+) -> Result<(), ProtocolValidationError> {
+    if &capability.session_binding != session_binding {
+        return Err(ProtocolValidationError::SessionBindingMismatch);
+    }
+    if capability.coordinator_credential_id != coordinator_credential_id
+        || capability.sandbox_credential_id != sandbox_credential_id
+    {
+        return Err(ProtocolValidationError::CredentialMismatch);
+    }
+    let claims = SessionCapabilityClaims {
+        protocol_version: capability.protocol_version,
+        session_binding: &capability.session_binding,
+        coordinator_credential_id: capability.coordinator_credential_id,
+        sandbox_credential_id: capability.sandbox_credential_id,
+    };
+    let claims = encode_payload(&claims)?;
+    if capability.capability_id != CapabilityId::new(sha256(&claims)) {
+        return Err(ProtocolValidationError::CapabilityDigestMismatch);
+    }
+    verify_payload(
+        ProtocolRecordKind::SessionRequestCapability,
+        &claims,
+        &capability.coordinator_signature,
+        coordinator_key,
+    )?;
+    Ok(())
+}
+
+/// Checks the certificate bytes and exact TLS identity tuple carried by a TLS credential.
+///
+/// # Errors
+///
+/// Returns an error for a stale tuple, role/subject mismatch, or certificate digest mismatch.
+pub fn verify_tls_credential(
+    credential: &TlsCredential,
+    expected_generation: &GenerationIdentity,
+    expected_role: TlsRole,
+    expected_subject: TlsSubjectId,
+) -> Result<(), ProtocolValidationError> {
+    if &credential.generation_identity != expected_generation {
+        return Err(ProtocolValidationError::GenerationMismatch);
+    }
+    if credential.role() != expected_role {
+        return Err(ProtocolValidationError::RoleMismatch);
+    }
+    if credential.subject_id() != expected_subject {
+        return Err(ProtocolValidationError::SubjectMismatch);
+    }
+    if credential.certificate_sha256 != CertificateDigest::new(sha256(&credential.certificate_der))
+    {
+        return Err(ProtocolValidationError::CertificateDigestMismatch);
+    }
+    Ok(())
+}
+
+#[derive(Clone, Debug)]
+pub struct VerifiedSession {
+    session_binding: SessionBinding,
+    capability: SessionRequestCapability,
+    sandbox_credential_id: ProtocolCredentialId,
+    coordinator_credential_id: ProtocolCredentialId,
+    sandbox_key: VerifyingKey,
+    coordinator_key: VerifyingKey,
+    session_anchor_key: VerifyingKey,
+}
+
+impl VerifiedSession {
+    /// Constructs an authority only after validating its manifest, credentials, and capability.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error when any key or identity tuple fails validation.
+    pub fn new(
+        trusted_manifest_digest: TrustManifestDigest,
+        tls_ca_sha256: CertificateDigest,
+        manifest: &TrustManifest,
+        session_binding: SessionBinding,
+        coordinator_credential: &ProtocolCredential,
+        sandbox_credential: &ProtocolCredential,
+        capability: SessionRequestCapability,
+    ) -> Result<Self, ProtocolValidationError> {
+        let generation = &session_binding.generation_identity;
+        let issuer =
+            verify_trust_manifest(manifest, trusted_manifest_digest, generation, tls_ca_sha256)?;
+        let coordinator_key = verify_protocol_credential(
+            coordinator_credential,
+            &issuer,
+            generation,
+            ProtocolCredentialRole::SessionCoordinator,
+            ProtocolSubjectId::SessionCoordinator(generation.coordinator_id),
+        )?;
+        let sandbox_key = verify_protocol_credential(
+            sandbox_credential,
+            &issuer,
+            generation,
+            ProtocolCredentialRole::AgentSandbox,
+            ProtocolSubjectId::AgentSandbox(generation.sandbox_id),
+        )?;
+        verify_session_capability(
+            &capability,
+            &session_binding,
+            coordinator_credential.credential_id,
+            sandbox_credential.credential_id,
+            &coordinator_key,
+        )?;
+        let anchor_bytes: [u8; 32] = session_binding
+            .session_anchor_public_key
+            .as_slice()
+            .try_into()
+            .map_err(|_| ProtocolValidationError::InvalidPublicKey)?;
+        let session_anchor_key = VerifyingKey::from_bytes(&anchor_bytes)
+            .map_err(|_| ProtocolValidationError::InvalidPublicKey)?;
+        Ok(Self {
+            session_binding,
+            capability,
+            sandbox_credential_id: sandbox_credential.credential_id,
+            coordinator_credential_id: coordinator_credential.credential_id,
+            sandbox_key,
+            coordinator_key,
+            session_anchor_key,
+        })
+    }
+
+    fn verify_sandbox_tuple(
+        &self,
+        session_binding: &SessionBinding,
+        capability: &SessionRequestCapability,
+        credential_id: ProtocolCredentialId,
+    ) -> Result<(), ProtocolValidationError> {
+        if session_binding != &self.session_binding {
+            return Err(ProtocolValidationError::SessionBindingMismatch);
+        }
+        if capability != &self.capability {
+            return Err(ProtocolValidationError::CapabilityMismatch);
+        }
+        if credential_id != self.sandbox_credential_id {
+            return Err(ProtocolValidationError::CredentialMismatch);
+        }
+        Ok(())
+    }
+
+    /// Verifies an exact signed request and returns its digest over accepted payload bytes.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, or tuple mismatch.
+    pub fn verify_request(
+        &self,
+        encoded: &[u8],
+    ) -> Result<(MailboxRequest, RequestDigest), ProtocolValidationError> {
+        let (request, payload_bytes) = decode_signed::<MailboxRequest>(encoded, &self.sandbox_key)?;
+        self.verify_sandbox_tuple(
+            request.session_binding(),
+            request.session_capability(),
+            request.sandbox_credential_id(),
+        )?;
+        Ok((request, request_digest(&payload_bytes)))
+    }
+
+    /// Verifies a signed cancellation for the exact request.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, tuple, or request mismatch.
+    pub fn verify_cancellation(
+        &self,
+        encoded: &[u8],
+        request_id: RequestId,
+    ) -> Result<MailboxCancellation, ProtocolValidationError> {
+        let (cancellation, _) = decode_signed::<MailboxCancellation>(encoded, &self.sandbox_key)?;
+        self.verify_sandbox_tuple(
+            &cancellation.session_binding,
+            &cancellation.session_capability,
+            cancellation.sandbox_credential_id,
+        )?;
+        if cancellation.request_id != request_id {
+            return Err(ProtocolValidationError::RequestMismatch);
+        }
+        Ok(cancellation)
+    }
+
+    /// Verifies a signed highest-contiguous acknowledgement for the exact request.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, tuple, or request mismatch.
+    pub fn verify_result_ack(
+        &self,
+        encoded: &[u8],
+        request_id: RequestId,
+        digest: RequestDigest,
+    ) -> Result<MailboxResultAck, ProtocolValidationError> {
+        let (ack, _) = decode_signed::<MailboxResultAck>(encoded, &self.sandbox_key)?;
+        self.verify_sandbox_tuple(
+            &ack.session_binding,
+            &ack.session_capability,
+            ack.sandbox_credential_id,
+        )?;
+        if ack.request_id != request_id || ack.request_sha256 != digest {
+            return Err(ProtocolValidationError::RequestMismatch);
+        }
+        Ok(ack)
+    }
+
+    /// Verifies one host-only Session Anchor decision for the exact request.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, tuple, or request mismatch.
+    pub fn verify_developer_decision(
+        &self,
+        encoded: &[u8],
+        request_id: RequestId,
+        digest: RequestDigest,
+    ) -> Result<DeveloperDecision, ProtocolValidationError> {
+        let (decision, _) = decode_signed::<DeveloperDecision>(encoded, &self.session_anchor_key)?;
+        if decision.session_binding != self.session_binding {
+            return Err(ProtocolValidationError::SessionBindingMismatch);
+        }
+        if decision.request_id != request_id || decision.request_sha256 != digest {
+            return Err(ProtocolValidationError::RequestMismatch);
+        }
+        Ok(decision)
+    }
+
+    /// Verifies one coordinator result chunk for the exact request.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, tuple, request, or size mismatch.
+    pub fn verify_result_chunk(
+        &self,
+        encoded: &[u8],
+        request_id: RequestId,
+        digest: RequestDigest,
+    ) -> Result<MailboxResultChunk, ProtocolValidationError> {
+        let (chunk, _) = decode_signed::<MailboxResultChunk>(encoded, &self.coordinator_key)?;
+        if chunk.bytes.len() > MAX_RESULT_CHUNK_BYTES {
+            return Err(ProtocolValidationError::ChunkTooLarge {
+                length: chunk.bytes.len(),
+            });
+        }
+        self.verify_coordinator_tuple(
+            &chunk.session_binding,
+            chunk.request_id,
+            chunk.request_sha256,
+            chunk.coordinator_credential_id,
+            request_id,
+            digest,
+        )?;
+        Ok(chunk)
+    }
+
+    /// Verifies one coordinator terminal result for the exact request.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error for signature, encoding, tuple, or request mismatch.
+    pub fn verify_result(
+        &self,
+        encoded: &[u8],
+        request_id: RequestId,
+        digest: RequestDigest,
+    ) -> Result<MailboxResult, ProtocolValidationError> {
+        let (result, _) = decode_signed::<MailboxResult>(encoded, &self.coordinator_key)?;
+        self.verify_coordinator_tuple(
+            &result.session_binding,
+            result.request_id,
+            result.request_sha256,
+            result.coordinator_credential_id,
+            request_id,
+            digest,
+        )?;
+        Ok(result)
+    }
+
+    fn verify_coordinator_tuple(
+        &self,
+        session_binding: &SessionBinding,
+        actual_request_id: RequestId,
+        actual_digest: RequestDigest,
+        credential_id: ProtocolCredentialId,
+        expected_request_id: RequestId,
+        expected_digest: RequestDigest,
+    ) -> Result<(), ProtocolValidationError> {
+        if session_binding != &self.session_binding {
+            return Err(ProtocolValidationError::SessionBindingMismatch);
+        }
+        if credential_id != self.coordinator_credential_id {
+            return Err(ProtocolValidationError::CredentialMismatch);
+        }
+        if actual_request_id != expected_request_id || actual_digest != expected_digest {
+            return Err(ProtocolValidationError::RequestMismatch);
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug, Default)]
+pub struct RequestReplayGuard {
+    admitted: BTreeSet<RequestId>,
+}
+
+impl RequestReplayGuard {
+    /// Verifies and records a request ID exactly once for this generation.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error when validation fails or the request ID was previously admitted.
+    pub fn admit(
+        &mut self,
+        session: &VerifiedSession,
+        encoded: &[u8],
+    ) -> Result<(MailboxRequest, RequestDigest), ProtocolValidationError> {
+        let (request, digest) = session.verify_request(encoded)?;
+        if !self.admitted.insert(request.request_id()) {
+            return Err(ProtocolValidationError::RequestReplay);
+        }
+        Ok((request, digest))
+    }
+
+    #[must_use]
+    pub fn len(&self) -> usize {
+        self.admitted.len()
+    }
+
+    #[must_use]
+    pub fn is_empty(&self) -> bool {
+        self.admitted.is_empty()
+    }
+}
+
+const _: () = assert!(MAX_UNACKNOWLEDGED_CHUNKS == 8);