mgm: Check management key algorithm when fetching from Yubikey

src/apdu.rs

@@ -82,6 +82,12 @@ impl Apdu {
         self
     }
 
+    /// Set this APDU's second parameter only
+    pub(crate) fn p2(&mut self, value: u8) -> &mut Self {
+        self.p2 = value;
+        self
+    }
+
     /// Set both parameters for this APDU
     pub fn params(&mut self, p1: u8, p2: u8) -> &mut Self {
         self.p1 = p1;

src/mgm.rs

@@ -39,6 +39,8 @@ use zeroize::Zeroize;
 use crate::{
     consts::{TAG_ADMIN_FLAGS_1, TAG_ADMIN_SALT, TAG_PROTECTED_MGM},
     metadata::{AdminData, ProtectedData},
+    piv::{ManagementSlotId, SlotAlgorithmId},
+    transaction::Transaction,
     yubikey::YubiKey,
 };
 use des::{
@@ -110,6 +112,27 @@ impl From<MgmAlgorithmId> for u8 {
     }
 }
 
+impl MgmAlgorithmId {
+    /// Looks up the algorithm for the given Yubikey's current management key.
+    #[cfg(feature = "untested")]
+    fn query(txn: &Transaction<'_>) -> Result<Self> {
+        match txn.get_metadata(crate::piv::SlotId::Management(ManagementSlotId::Management)) {
+            Ok(metadata) => match metadata.algorithm {
+                SlotAlgorithmId::Management(alg) => Ok(alg),
+                // We specifically queried the management key slot; getting a known
+                // non-management algorithm back from the Yubikey is invalid.
+                _ => Err(Error::InvalidObject),
+            },
+            // Firmware versions without `GET METADATA` only support 3DES.
+            Err(Error::NotSupported) => Ok(MgmAlgorithmId::ThreeDes),
+            // `Error::AlgorithmError` only occurs when a new algorithm is encountered.
+            Err(Error::AlgorithmError) => Err(Error::NotSupported),
+            // Raise other errors as-is.
+            Err(e) => Err(e),
+        }
+    }
+}
+
 /// Management Key (MGM).
 ///
 /// This key is used to authenticate to the management applet running on
@@ -155,6 +178,12 @@ impl MgmKey {
     pub fn get_derived(yubikey: &mut YubiKey, pin: &[u8]) -> Result<Self> {
         let txn = yubikey.begin_transaction()?;
 
+        // Check the key algorithm.
+        let alg = MgmAlgorithmId::query(&txn)?;
+        if alg != MgmAlgorithmId::ThreeDes {
+            return Err(Error::NotSupported);
+        }
+
         // recover management key
         let admin_data = AdminData::read(&txn)?;
         let salt = admin_data.get_item(TAG_ADMIN_SALT)?;
@@ -179,6 +208,12 @@ impl MgmKey {
     pub fn get_protected(yubikey: &mut YubiKey) -> Result<Self> {
         let txn = yubikey.begin_transaction()?;
 
+        // Check the key algorithm.
+        let alg = MgmAlgorithmId::query(&txn)?;
+        if alg != MgmAlgorithmId::ThreeDes {
+            return Err(Error::NotSupported);
+        }
+
         let protected_data = ProtectedData::read(&txn)
             .inspect_err(|e| error!("could not read protected data (err: {:?})", e))?;
 

src/piv.rs

@@ -45,7 +45,6 @@
 use crate::{
     apdu::{Ins, StatusWords},
     certificate::{self, Certificate},
-    consts::CB_OBJ_MAX,
     error::{Error, Result},
     mgm::MgmAlgorithmId,
     policy::{PinPolicy, TouchPolicy},
@@ -75,6 +74,9 @@ use {
 #[cfg(feature = "untested")]
 use zeroize::Zeroizing;
 
+#[cfg(feature = "untested")]
+use crate::consts::CB_OBJ_MAX;
+
 /// PIV Applet Name
 pub(crate) const APPLET_NAME: &str = "PIV";
 
@@ -925,21 +927,8 @@ pub fn decrypt_data(
 /// Read metadata
 pub fn metadata(yubikey: &mut YubiKey, slot: SlotId) -> Result<SlotMetadata> {
     let txn = yubikey.begin_transaction()?;
-    let templ = [0, Ins::GetMetadata.code(), 0, slot.into()];
-
-    let response = txn.transfer_data(&templ, &[], CB_OBJ_MAX)?;
-
-    if !response.is_success() {
-        if response.status_words() == StatusWords::NotSupportedError {
-            return Err(Error::NotSupported); // Requires firmware 5.2.3
-        } else {
-            return Err(Error::GenericError);
-        }
-    }
-
-    let buf = Buffer::new(response.data().into());
 
-    SlotMetadata::try_from(buf)
+    txn.get_metadata(slot)
 }
 
 /// Metadata from a slot

src/transaction.rs

@@ -168,6 +168,25 @@ impl<'tx> Transaction<'tx> {
         }
     }
 
+    /// Read metadata
+    pub(crate) fn get_metadata(&self, slot: SlotId) -> Result<piv::SlotMetadata> {
+        let response = Apdu::new(Ins::GetMetadata)
+            .p2(slot.into())
+            .transmit(self, CB_OBJ_MAX)?;
+
+        if !response.is_success() {
+            if response.status_words() == StatusWords::NotSupportedError {
+                return Err(Error::NotSupported); // Requires firmware 5.2.3
+            } else {
+                return Err(Error::GenericError);
+            }
+        }
+
+        let buf = Buffer::new(response.data().into());
+
+        piv::SlotMetadata::try_from(buf)
+    }
+
     /// Verify device PIN.
     pub fn verify_pin(&self, pin: &[u8]) -> Result<()> {
         if pin.len() > CB_PIN_MAX {