Added support for "dont-enforce-user-presence-and-sign" (0x08)

This change adds support for the control byte value 0x08, which is the
value for "dont-enforce-user-presence-and-sign". In this mode, user
presence is not enforced but a signature is still created.

src/main/java/com/ledger/u2f/NullPresence.java

@@ -6,6 +6,12 @@
  */
 public class NullPresence implements Presence {
     @Override
-    public void verify_user_presence() {
+    public byte enforce_user_presence() {
+        return FLAG_USER_PRESENT;
+    }
+
+    @Override
+    public byte check_user_presence() {
+        return 0;
     }
 }

src/main/java/com/ledger/u2f/OneShotPresence.java

@@ -29,10 +29,22 @@ public class OneShotPresence implements Presence {
     }
 
     @Override
-    public void verify_user_presence() {
-        if (did_verify_flag[0] != 0) {
+    public byte enforce_user_presence() {
+        byte presence = check_user_presence();
+
+        if ((presence & FLAG_USER_PRESENT) != FLAG_USER_PRESENT) {
             ISOException.throwIt(ISO7816.SW_CONDITIONS_NOT_SATISFIED);
         }
+
+        return presence;
+    }
+
+    @Override
+    public byte check_user_presence() {
+        if (did_verify_flag[0] != 0) {
+            return 0;
+        }
         did_verify_flag[0] = 1;
+        return FLAG_USER_PRESENT;
     }
 }

src/main/java/com/ledger/u2f/Presence.java

@@ -1,6 +1,36 @@
 package com.ledger.u2f;
 
 public interface Presence {
+    /** A user is present.
+     *
+     * This means that someone interacted with the
+     * authenticator while performing this operation.
+     */
+    byte FLAG_USER_PRESENT = (byte)0x01;
 
-    void verify_user_presence();
+    /** The user was verified. From webauthn.
+     *
+     * This means that the user has verified themselves
+     * to the authenticator using, for example, their
+     * fingerprint or a PIN.
+     */
+    byte FLAG_USER_VERIFIED = (byte)0x04;
+
+    /**
+     * Waits for user presence, throwing an exception if that
+     * is impossible or if there is a timeout.
+     *
+     * @return the value of the user presence byte
+     *         in the FIDO U2F signature response.
+     */
+    byte enforce_user_presence();
+
+    /**
+     * Checks user presence. Should not throw an exception.
+     * Returns immediately.
+     *
+     * @return the value of the user presence byte
+     *         in the FIDO U2F signature response.
+     */
+    byte check_user_presence();
 }

src/main/java/com/ledger/u2f/U2FApplet.java

@@ -71,8 +71,9 @@ public class U2FApplet extends Applet implements ExtendedLength {
     private static final byte TRANSPORT_NOT_EXTENDED_CERT = (byte)3;
     private static final byte TRANSPORT_NOT_EXTENDED_SIGNATURE = (byte)4;
 
-    private static final byte P1_SIGN_OPERATION = (byte)0x03;
+    private static final byte P1_ENFORCE_PRESENCE_AND_SIGN = (byte)0x03;
     private static final byte P1_SIGN_CHECK_ONLY = (byte)0x07;
+    private static final byte P1_IGNORE_PRESENCE_AND_SIGN = (byte)0x08;
 
     private static final byte ENROLL_LEGACY_VERSION = (byte)0x05;
     private static final byte RFU_ENROLL_SIGNED_VERSION[] = { (byte)0x00 };
@@ -83,8 +84,6 @@ public class U2FApplet extends Applet implements ExtendedLength {
     private static final short APDU_CHALLENGE_OFFSET = (short)0;
     private static final short APDU_APPLICATION_PARAMETER_OFFSET = (short)32;
 
-    private static final byte FLAG_USER_PRESENCE_VERIFIED = (byte)0x01;
-
     private static final short FIDO_SW_TEST_OF_PRESENCE_REQUIRED = ISO7816.SW_CONDITIONS_NOT_SATISFIED;
     private static final short FIDO_SW_INVALID_KEY_HANDLE = ISO7816.SW_WRONG_DATA;
 
@@ -163,7 +162,7 @@ private void handleEnroll(APDU apdu) throws ISOException {
         }
 
         // Deny if user presence cannot be validated
-        presence.verify_user_presence();
+        presence.enforce_user_presence();
 
         // Generate the key pair
         if (localPrivateTransient) {
@@ -208,14 +207,19 @@ private void handleSign(APDU apdu) throws ISOException {
         short dataOffset = apdu.getOffsetCdata();
         byte p1 = buffer[ISO7816.OFFSET_P1];
         boolean sign = false;
+        boolean enforce_presence = false;
         short keyHandleLength;
         boolean extendedLength = (dataOffset != ISO7816.OFFSET_CDATA);
         short outOffset = SCRATCH_PAD;
         if (len < 65) {
             ISOException.throwIt(ISO7816.SW_WRONG_LENGTH);
         }
         switch(p1) {
-        case P1_SIGN_OPERATION:
+        case P1_ENFORCE_PRESENCE_AND_SIGN:
+            sign = true;
+            enforce_presence = true;
+            break;
+        case P1_IGNORE_PRESENCE_AND_SIGN:
             sign = true;
             break;
         case P1_SIGN_CHECK_ONLY:
@@ -237,15 +241,15 @@ private void handleSign(APDU apdu) throws ISOException {
             ISOException.throwIt(FIDO_SW_TEST_OF_PRESENCE_REQUIRED);
         }
 
-        // If signing, only proceed if user presence can be validated
-        presence.verify_user_presence();
+        if (enforce_presence) {
+            scratch[outOffset++] = presence.enforce_user_presence();
+        } else {
+            scratch[outOffset++] = presence.check_user_presence();
+        }
 
-        // Increase the counter
+        // Increase the signature counter
         counter.inc();
 
-        // Prepare reply
-        scratch[outOffset++] = FLAG_USER_PRESENCE_VERIFIED;
-
         outOffset = counter.writeValue(scratch, outOffset);
 
         localSignature.init(localPrivateKey, Signature.MODE_SIGN);