Merge pull request #281 from kaczmarczyck/enterprise-attestation

Enterprise attestation

README.md

@@ -125,6 +125,9 @@ a few things you can personalize:
     length.
 1.  Increase the `MAX_CRED_BLOB_LENGTH` in `ctap/mod.rs`, if you expect blobs
     bigger than the default value.
+1.  Implement enterprise attestation. This can be as easy as setting
+    ENTERPRISE_ATTESTATION_MODE in `ctap/mod.rs`. If you want to use a different
+    attestation type than batch attestation, you have to implement it first.
 
 ### 3D printed enclosure
 

src/ctap/command.rs

@@ -161,7 +161,7 @@ pub struct AuthenticatorMakeCredentialParameters {
     pub options: MakeCredentialOptions,
     pub pin_uv_auth_param: Option<Vec<u8>>,
     pub pin_uv_auth_protocol: Option<u64>,
-    pub enterprise_attestation: Option<bool>,
+    pub enterprise_attestation: Option<u64>,
 }
 
 impl TryFrom<cbor::Value> for AuthenticatorMakeCredentialParameters {
@@ -219,7 +219,7 @@ impl TryFrom<cbor::Value> for AuthenticatorMakeCredentialParameters {
 
         let pin_uv_auth_param = pin_uv_auth_param.map(extract_byte_string).transpose()?;
         let pin_uv_auth_protocol = pin_uv_auth_protocol.map(extract_unsigned).transpose()?;
-        let enterprise_attestation = enterprise_attestation.map(extract_bool).transpose()?;
+        let enterprise_attestation = enterprise_attestation.map(extract_unsigned).transpose()?;
 
         Ok(AuthenticatorMakeCredentialParameters {
             client_data_hash,
@@ -601,7 +601,7 @@ mod test {
             0x05 => cbor_array![],
             0x08 => vec![0x12, 0x34],
             0x09 => 1,
-            0x0A => true,
+            0x0A => 2,
         };
         let returned_make_credential_parameters =
             AuthenticatorMakeCredentialParameters::try_from(cbor_value).unwrap();
@@ -635,7 +635,7 @@ mod test {
             options,
             pin_uv_auth_param: Some(vec![0x12, 0x34]),
             pin_uv_auth_protocol: Some(1),
-            enterprise_attestation: Some(true),
+            enterprise_attestation: Some(2),
         };
 
         assert_eq!(

src/ctap/config_command.rs

@@ -12,15 +12,27 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use super::check_pin_uv_auth_protocol;
 use super::command::AuthenticatorConfigParameters;
 use super::data_formats::{ConfigSubCommand, ConfigSubCommandParams, SetMinPinLengthParams};
 use super::pin_protocol_v1::PinProtocolV1;
 use super::response::ResponseData;
 use super::status_code::Ctap2StatusCode;
 use super::storage::PersistentStore;
+use super::{check_pin_uv_auth_protocol, ENTERPRISE_ATTESTATION_MODE};
 use alloc::vec;
 
+/// Processes the subcommand enableEnterpriseAttestation for AuthenticatorConfig.
+fn process_enable_enterprise_attestation(
+    persistent_store: &mut PersistentStore,
+) -> Result<ResponseData, Ctap2StatusCode> {
+    if ENTERPRISE_ATTESTATION_MODE.is_some() {
+        persistent_store.enable_enterprise_attestation()?;
+        Ok(ResponseData::AuthenticatorConfig)
+    } else {
+        Err(Ctap2StatusCode::CTAP1_ERR_INVALID_PARAMETER)
+    }
+}
+
 /// Processes the subcommand setMinPINLength for AuthenticatorConfig.
 fn process_set_min_pin_length(
     persistent_store: &mut PersistentStore,
@@ -85,6 +97,9 @@ pub fn process_config(
     }
 
     match sub_command {
+        ConfigSubCommand::EnableEnterpriseAttestation => {
+            process_enable_enterprise_attestation(persistent_store)
+        }
         ConfigSubCommand::SetMinPinLength => {
             if let Some(ConfigSubCommandParams::SetMinPinLength(params)) = sub_command_params {
                 process_set_min_pin_length(persistent_store, params)
@@ -101,6 +116,34 @@ mod test {
     use super::*;
     use crypto::rng256::ThreadRng256;
 
+    #[test]
+    fn test_process_enable_enterprise_attestation() {
+        let mut rng = ThreadRng256 {};
+        let mut persistent_store = PersistentStore::new(&mut rng);
+        let key_agreement_key = crypto::ecdh::SecKey::gensk(&mut rng);
+        let pin_uv_auth_token = [0x55; 32];
+        let mut pin_protocol_v1 = PinProtocolV1::new_test(key_agreement_key, pin_uv_auth_token);
+
+        let config_params = AuthenticatorConfigParameters {
+            sub_command: ConfigSubCommand::EnableEnterpriseAttestation,
+            sub_command_params: None,
+            pin_uv_auth_param: None,
+            pin_uv_auth_protocol: None,
+        };
+        let config_response =
+            process_config(&mut persistent_store, &mut pin_protocol_v1, config_params);
+
+        if ENTERPRISE_ATTESTATION_MODE.is_some() {
+            assert_eq!(config_response, Ok(ResponseData::AuthenticatorConfig));
+            assert_eq!(persistent_store.enterprise_attestation(), Ok(true));
+        } else {
+            assert_eq!(
+                config_response,
+                Err(Ctap2StatusCode::CTAP1_ERR_INVALID_PARAMETER)
+            );
+        }
+    }
+
     fn create_min_pin_config_params(
         min_pin_length: u8,
         min_pin_length_rp_ids: Option<Vec<String>>,

src/ctap/data_formats.rs

@@ -939,6 +939,24 @@ impl From<SetMinPinLengthParams> for cbor::Value {
     }
 }
 
+#[derive(Debug, PartialEq)]
+pub enum EnterpriseAttestationMode {
+    VendorFacilitated = 0x01,
+    PlatformManaged = 0x02,
+}
+
+impl TryFrom<u64> for EnterpriseAttestationMode {
+    type Error = Ctap2StatusCode;
+
+    fn try_from(value: u64) -> Result<Self, Ctap2StatusCode> {
+        match value {
+            1 => Ok(EnterpriseAttestationMode::VendorFacilitated),
+            2 => Ok(EnterpriseAttestationMode::PlatformManaged),
+            _ => Err(Ctap2StatusCode::CTAP2_ERR_INVALID_OPTION),
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(test, derive(IntoEnumIterator))]
 pub enum CredentialManagementSubCommand {
@@ -1795,6 +1813,26 @@ mod test {
         assert_eq!(cbor::Value::from(config_sub_command_params), cbor_params);
     }
 
+    #[test]
+    fn test_from_enterprise_attestation_mode() {
+        assert_eq!(
+            EnterpriseAttestationMode::try_from(0),
+            Err(Ctap2StatusCode::CTAP2_ERR_INVALID_OPTION),
+        );
+        assert_eq!(
+            EnterpriseAttestationMode::try_from(1),
+            Ok(EnterpriseAttestationMode::VendorFacilitated),
+        );
+        assert_eq!(
+            EnterpriseAttestationMode::try_from(2),
+            Ok(EnterpriseAttestationMode::PlatformManaged),
+        );
+        assert_eq!(
+            EnterpriseAttestationMode::try_from(3),
+            Err(Ctap2StatusCode::CTAP2_ERR_INVALID_OPTION),
+        );
+    }
+
     #[test]
     fn test_from_into_cred_management_sub_command() {
         let cbor_sub_command: cbor::Value = cbor_int!(0x01);

src/ctap/mod.rs

@@ -36,10 +36,10 @@ use self::command::{
 use self::config_command::process_config;
 use self::credential_management::process_credential_management;
 use self::data_formats::{
-    AuthenticatorTransport, CoseKey, CredentialProtectionPolicy, GetAssertionExtensions,
+    AuthenticatorTransport, CoseKey, CredentialProtectionPolicy, EnterpriseAttestationMode,
-    PackedAttestationStatement, PublicKeyCredentialDescriptor, PublicKeyCredentialParameter,
+    GetAssertionExtensions, PackedAttestationStatement, PublicKeyCredentialDescriptor,
-    PublicKeyCredentialSource, PublicKeyCredentialType, PublicKeyCredentialUserEntity,
+    PublicKeyCredentialParameter, PublicKeyCredentialSource, PublicKeyCredentialType,
-    SignatureAlgorithm,
+    PublicKeyCredentialUserEntity, SignatureAlgorithm,
 };
 use self::hid::ChannelID;
 use self::large_blobs::{LargeBlobs, MAX_MSG_SIZE};
@@ -61,6 +61,7 @@ use alloc::vec::Vec;
 use arrayref::array_ref;
 use byteorder::{BigEndian, ByteOrder};
 use cbor::cbor_map_options;
+use core::convert::TryFrom;
 #[cfg(feature = "debug_ctap")]
 use core::fmt::Write;
 use crypto::cbc::{cbc_decrypt, cbc_encrypt};
@@ -74,9 +75,11 @@ use libtock_drivers::crp;
 use libtock_drivers::timer::{ClockValue, Duration};
 
 // This flag enables or disables basic attestation for FIDO2. U2F is unaffected by
-// this setting. The basic attestation uses the signing key from key_material.rs
+// this setting. The basic attestation uses the signing key configured with a
-// as a batch key. Turn it on if you want attestation. In this case, be aware that
+// vendor command as a batch key. If you turn batch attestation on, be aware that
-// it is your responsibility to generate your own key material and keep it secret.
+// it is your responsibility to safely generate and store the key material. Also,
+// the batches must have size of at least 100k authenticators before using new
+// key material.
 const USE_BATCH_ATTESTATION: bool = false;
 // The signature counter is currently implemented as a global counter, if you set
 // this flag to true. The spec strongly suggests to have per-credential-counters,
@@ -86,6 +89,21 @@ const USE_BATCH_ATTESTATION: bool = false;
 // solution is a compromise to be compatible with U2F and not wasting storage.
 const USE_SIGNATURE_COUNTER: bool = true;
 pub const INITIAL_SIGNATURE_COUNTER: u32 = 1;
+// This flag allows usage of enterprise attestation. For privacy reasons, it is
+// disabled by default. You can choose between
+// - EnterpriseAttestationMode::VendorFacilitated,
+// - EnterpriseAttestationMode::PlatformManaged.
+// For VendorFacilitated, choose an appriopriate ENTERPRISE_RP_ID_LIST.
+// To enable the feature, send the subcommand enableEnterpriseAttestation in
+// AuthenticatorConfig. An enterprise might want to customize the type of
+// attestation that is used. OpenSK defaults to batch attestation. Configuring
+// individual certificates then makes authenticators identifiable. Do NOT set
+// USE_BATCH_ATTESTATION to true at the same time in this case! The code asserts
+// that you don't use the same key material for batch and enterprise attestation.
+// If you implement your own enterprise attestation mechanism, and you want batch
+// attestation at the same time, proceed carefully and remove the assertion.
+pub const ENTERPRISE_ATTESTATION_MODE: Option<EnterpriseAttestationMode> = None;
+const ENTERPRISE_RP_ID_LIST: &[&str] = &[];
 // Our credential ID consists of
 // - 16 byte initialization vector for AES-256,
 // - 32 byte ECDSA private key for the credential,
@@ -308,6 +326,11 @@ where
         check_user_presence: CheckUserPresence,
         now: ClockValue,
     ) -> CtapState<'a, R, CheckUserPresence> {
+        #[allow(clippy::assertions_on_constants)]
+        {
+            assert!(!USE_BATCH_ATTESTATION || ENTERPRISE_ATTESTATION_MODE.is_none());
+        }
+
         let persistent_store = PersistentStore::new(rng);
         let pin_protocol_v1 = PinProtocolV1::new(rng);
         CtapState {
@@ -562,7 +585,7 @@ where
             options,
             pin_uv_auth_param,
             pin_uv_auth_protocol,
-            enterprise_attestation: _,
+            enterprise_attestation,
         } = make_credential_params;
 
         self.pin_uv_auth_precheck(&pin_uv_auth_param, pin_uv_auth_protocol, cid)?;
@@ -572,6 +595,26 @@ where
         }
 
         let rp_id = rp.rp_id;
+        let ep_att = if let Some(enterprise_attestation) = enterprise_attestation {
+            let authenticator_mode =
+                ENTERPRISE_ATTESTATION_MODE.ok_or(Ctap2StatusCode::CTAP1_ERR_INVALID_PARAMETER)?;
+            if !self.persistent_store.enterprise_attestation()? {
+                return Err(Ctap2StatusCode::CTAP1_ERR_INVALID_PARAMETER);
+            }
+            match (
+                EnterpriseAttestationMode::try_from(enterprise_attestation)?,
+                authenticator_mode,
+            ) {
+                (
+                    EnterpriseAttestationMode::PlatformManaged,
+                    EnterpriseAttestationMode::PlatformManaged,
+                ) => ENTERPRISE_RP_ID_LIST.contains(&rp_id.as_str()),
+                _ => true,
+            }
+        } else {
+            false
+        };
+
         let mut cred_protect_policy = extensions.cred_protect;
         if cred_protect_policy.unwrap_or(CredentialProtectionPolicy::UserVerificationOptional)
             < DEFAULT_CRED_PROTECT.unwrap_or(CredentialProtectionPolicy::UserVerificationOptional)
@@ -723,7 +766,7 @@ where
         let mut signature_data = auth_data.clone();
         signature_data.extend(client_data_hash);
 
-        let (signature, x5c) = if USE_BATCH_ATTESTATION {
+        let (signature, x5c) = if USE_BATCH_ATTESTATION || ep_att {
             let attestation_private_key = self
                 .persistent_store
                 .attestation_private_key()?
@@ -750,11 +793,13 @@ where
             x5c,
             ecdaa_key_id: None,
         };
+        let ep_att = if ep_att { Some(true) } else { None };
         Ok(ResponseData::AuthenticatorMakeCredential(
             AuthenticatorMakeCredentialResponse {
                 fmt: String::from("packed"),
                 auth_data,
                 att_stmt: attestation_statement,
+                ep_att,
                 large_blob_key,
             },
         ))
@@ -1026,6 +1071,12 @@ where
         options_map.insert(String::from("up"), true);
         options_map.insert(String::from("pinUvAuthToken"), true);
         options_map.insert(String::from("largeBlobs"), true);
+        if ENTERPRISE_ATTESTATION_MODE.is_some() {
+            options_map.insert(
+                String::from("ep"),
+                self.persistent_store.enterprise_attestation()?,
+            );
+        }
         options_map.insert(String::from("authnrCfg"), true);
         options_map.insert(String::from("credMgmt"), true);
         options_map.insert(String::from("setMinPINLength"), true);
@@ -1227,6 +1278,7 @@ mod test {
                     fmt,
                     auth_data,
                     att_stmt,
+                    ep_att,
                     large_blob_key,
                 } = make_credential_response;
                 // The expected response is split to only assert the non-random parts.
@@ -1247,6 +1299,7 @@ mod test {
                     &auth_data[auth_data.len() - expected_extension_cbor.len()..auth_data.len()],
                     expected_extension_cbor
                 );
+                assert!(ep_att.is_none());
                 assert_eq!(att_stmt.alg, SignatureAlgorithm::ES256 as i64);
                 assert_eq!(large_blob_key, None);
             }
@@ -1276,12 +1329,13 @@ mod test {
                     String::from("largeBlobKey"),
                 ]],
             0x03 => ctap_state.persistent_store.aaguid().unwrap(),
-            0x04 => cbor_map! {
+            0x04 => cbor_map_options! {
                 "rk" => true,
                 "clientPin" => false,
                 "up" => true,
                 "pinUvAuthToken" => true,
                 "largeBlobs" => true,
+                "ep" => ENTERPRISE_ATTESTATION_MODE.map(|_| false),
                 "authnrCfg" => true,
                 "credMgmt" => true,
                 "setMinPINLength" => true,

src/ctap/response.rs

@@ -61,6 +61,7 @@ pub struct AuthenticatorMakeCredentialResponse {
     pub fmt: String,
     pub auth_data: Vec<u8>,
     pub att_stmt: PackedAttestationStatement,
+    pub ep_att: Option<bool>,
     pub large_blob_key: Option<Vec<u8>>,
 }
 
@@ -70,6 +71,7 @@ impl From<AuthenticatorMakeCredentialResponse> for cbor::Value {
             fmt,
             auth_data,
             att_stmt,
+            ep_att,
             large_blob_key,
         } = make_credential_response;
 
@@ -77,6 +79,7 @@ impl From<AuthenticatorMakeCredentialResponse> for cbor::Value {
             0x01 => fmt,
             0x02 => auth_data,
             0x03 => att_stmt,
+            0x04 => ep_att,
             0x05 => large_blob_key,
         }
     }
@@ -320,6 +323,7 @@ mod test {
             fmt: "packed".to_string(),
             auth_data: vec![0xAD],
             att_stmt,
+            ep_att: Some(true),
             large_blob_key: Some(vec![0x1B]),
         };
         let response_cbor: Option<cbor::Value> =
@@ -328,6 +332,7 @@ mod test {
             0x01 => "packed",
             0x02 => vec![0xAD],
             0x03 => cbor_packed_attestation_statement,
+            0x04 => true,
             0x05 => vec![0x1B],
         };
         assert_eq!(response_cbor, Some(expected_cbor));

src/ctap/storage.rs

@@ -56,7 +56,7 @@ const MAX_SUPPORTED_RESIDENT_KEYS: usize = 150;
 
 const MAX_PIN_RETRIES: u8 = 8;
 const DEFAULT_MIN_PIN_LENGTH: u8 = 4;
-const DEFAULT_MIN_PIN_LENGTH_RP_IDS: Vec<String> = Vec::new();
+const DEFAULT_MIN_PIN_LENGTH_RP_IDS: &[&str] = &[];
 // This constant is an attempt to limit storage requirements. If you don't set it to 0,
 // the stored strings can still be unbounded, but that is true for all RP IDs.
 pub const MAX_RP_IDS_LENGTH: usize = 8;
@@ -439,12 +439,17 @@ impl PersistentStore {
     /// Returns the list of RP IDs that are used to check if reading the minimum PIN length is
     /// allowed.
     pub fn min_pin_length_rp_ids(&self) -> Result<Vec<String>, Ctap2StatusCode> {
-        let rp_ids = self
+        let rp_ids = self.store.find(key::MIN_PIN_LENGTH_RP_IDS)?.map_or_else(
-            .store
+            || {
-            .find(key::MIN_PIN_LENGTH_RP_IDS)?
+                Some(
-            .map_or(Some(DEFAULT_MIN_PIN_LENGTH_RP_IDS), |value| {
+                    DEFAULT_MIN_PIN_LENGTH_RP_IDS
-                deserialize_min_pin_length_rp_ids(&value)
+                        .iter()
-            });
+                        .map(|&s| String::from(s))
+                        .collect(),
+                )
+            },
+            |value| deserialize_min_pin_length_rp_ids(&value),
+        );
         debug_assert!(rp_ids.is_some());
         Ok(rp_ids.unwrap_or_default())
     }
@@ -455,7 +460,8 @@ impl PersistentStore {
         min_pin_length_rp_ids: Vec<String>,
     ) -> Result<(), Ctap2StatusCode> {
         let mut min_pin_length_rp_ids = min_pin_length_rp_ids;
-        for rp_id in DEFAULT_MIN_PIN_LENGTH_RP_IDS {
+        for &rp_id in DEFAULT_MIN_PIN_LENGTH_RP_IDS.iter() {
+            let rp_id = String::from(rp_id);
             if !min_pin_length_rp_ids.contains(&rp_id) {
                 min_pin_length_rp_ids.push(rp_id);
             }
@@ -610,6 +616,23 @@ impl PersistentStore {
     pub fn force_pin_change(&mut self) -> Result<(), Ctap2StatusCode> {
         Ok(self.store.insert(key::FORCE_PIN_CHANGE, &[])?)
     }
+
+    /// Returns whether enterprise attestation is enabled.
+    pub fn enterprise_attestation(&self) -> Result<bool, Ctap2StatusCode> {
+        match self.store.find(key::ENTERPRISE_ATTESTATION)? {
+            None => Ok(false),
+            Some(value) if value.is_empty() => Ok(true),
+            _ => Err(Ctap2StatusCode::CTAP2_ERR_VENDOR_INTERNAL_ERROR),
+        }
+    }
+
+    /// Marks enterprise attestation as enabled.
+    pub fn enable_enterprise_attestation(&mut self) -> Result<(), Ctap2StatusCode> {
+        if !self.enterprise_attestation()? {
+            self.store.insert(key::ENTERPRISE_ATTESTATION, &[])?;
+        }
+        Ok(())
+    }
 }
 
 impl From<persistent_store::StoreError> for Ctap2StatusCode {
@@ -1186,7 +1209,8 @@ mod test {
             persistent_store.set_min_pin_length_rp_ids(rp_ids.clone()),
             Ok(())
         );
-        for rp_id in DEFAULT_MIN_PIN_LENGTH_RP_IDS {
+        for &rp_id in DEFAULT_MIN_PIN_LENGTH_RP_IDS.iter() {
+            let rp_id = String::from(rp_id);
             if !rp_ids.contains(&rp_id) {
                 rp_ids.push(rp_id);
             }
@@ -1308,6 +1332,18 @@ mod test {
         assert!(!persistent_store.has_force_pin_change().unwrap());
     }
 
+    #[test]
+    fn test_enterprise_attestation() {
+        let mut rng = ThreadRng256 {};
+        let mut persistent_store = PersistentStore::new(&mut rng);
+
+        assert!(!persistent_store.enterprise_attestation().unwrap());
+        assert_eq!(persistent_store.enable_enterprise_attestation(), Ok(()));
+        assert!(persistent_store.enterprise_attestation().unwrap());
+        persistent_store.reset(&mut rng).unwrap();
+        assert!(!persistent_store.enterprise_attestation().unwrap());
+    }
+
     #[test]
     fn test_serialize_deserialize_credential() {
         let mut rng = ThreadRng256 {};

src/ctap/storage/key.rs

@@ -93,7 +93,10 @@ make_partition! {
     /// The stored large blob can be too big for one key, so it has to be sharded.
     LARGE_BLOB_SHARDS = 2000..2004;
 
-    /// If this entry exists and equals 1, the PIN needs to be changed.
+    /// If this entry exists and is empty, enterprise attestation is enabled.
+    ENTERPRISE_ATTESTATION = 2039;
+
+    /// If this entry exists and is empty, the PIN needs to be changed.
     FORCE_PIN_CHANGE = 2040;
 
     /// The secret of the CredRandom feature.