If no key flags subpacket is present allow all key flags, fixes mailvelope keys

OpenKeychain-Test/src/test/resources/test-keys/mailvelope_07_no_key_flags.asc

@@ -0,0 +1,20 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+Version: Mailvelope v0.7.0
+Comment: Email security by Mailvelope - http://www.mailvelope.com
+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+=hu6f
+-----END PGP PUBLIC KEY BLOCK----- 

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/UncachedPublicKey.java

@@ -22,6 +22,7 @@ import org.spongycastle.asn1.ASN1ObjectIdentifier;
 import org.spongycastle.asn1.nist.NISTNamedCurves;
 import org.spongycastle.asn1.teletrust.TeleTrusTNamedCurves;
 import org.spongycastle.bcpg.ECPublicBCPGKey;
+import org.spongycastle.bcpg.SignatureSubpacketTags;
 import org.spongycastle.bcpg.sig.KeyFlags;
 import org.spongycastle.openpgp.PGPPublicKey;
 import org.spongycastle.openpgp.PGPSignature;
@@ -208,21 +209,24 @@ public class UncachedPublicKey {
     }
 
     /**
-     * Get all key usage flags
-     *
-     * TODO make this safe
+     * Get all key usage flags.
+     * If at least one key flag subpacket is present return these.
+     * If no subpacket is present it returns null.
      */
     @SuppressWarnings("unchecked")
-    public int getKeyUsage() {
-        if(mCacheUsage == null) {
-            mCacheUsage = 0;
+    public Integer getKeyUsage() {
+        if (mCacheUsage == null) {
             for (PGPSignature sig : new IterableIterator<PGPSignature>(mPublicKey.getSignatures())) {
                 if (mPublicKey.isMasterKey() && sig.getKeyID() != mPublicKey.getKeyID()) {
                     continue;
                 }
 
                 PGPSignatureSubpacketVector hashed = sig.getHashedSubPackets();
-                if (hashed != null) {
+                if (hashed != null && hashed.getSubpacket(SignatureSubpacketTags.KEY_FLAGS) != null) {
+                    // init if at least one key flag subpacket has been found
+                    if (mCacheUsage == null) {
+                        mCacheUsage = 0;
+                    }
                     mCacheUsage |= hashed.getKeyFlags();
                 }
             }
@@ -230,38 +234,57 @@ public class UncachedPublicKey {
         return mCacheUsage;
     }
 
-    public boolean canAuthenticate() {
-        return (getKeyUsage() & KeyFlags.AUTHENTICATION) != 0;
-    }
-
     public boolean canCertify() {
-        return (getKeyUsage() & KeyFlags.CERTIFY_OTHER) != 0;
-    }
-
-    public boolean canEncrypt() {
-        if (!mPublicKey.isEncryptionKey()) {
-            return false;
+        // if key flags subpacket is available, honor it!
+        if (getKeyUsage() != null) {
+            return (getKeyUsage() & KeyFlags.CERTIFY_OTHER) != 0;
         }
 
-        // special cases
-        if (mPublicKey.getAlgorithm() == PGPPublicKey.ELGAMAL_ENCRYPT) {
+        if (mPublicKey.getAlgorithm() == PGPPublicKey.RSA_GENERAL
+                || mPublicKey.getAlgorithm() == PGPPublicKey.RSA_SIGN
+                || mPublicKey.getAlgorithm() == PGPPublicKey.ECDSA) {
             return true;
         }
 
-        if (mPublicKey.getAlgorithm() == PGPPublicKey.RSA_ENCRYPT) {
-            return true;
-        }
-
-        return (getKeyUsage() & (KeyFlags.ENCRYPT_COMMS | KeyFlags.ENCRYPT_STORAGE)) != 0;
+        return false;
     }
 
     public boolean canSign() {
-        // special case
-        if (mPublicKey.getAlgorithm() == PGPPublicKey.RSA_SIGN) {
+        // if key flags subpacket is available, honor it!
+        if (getKeyUsage() != null) {
+            return (getKeyUsage() & KeyFlags.SIGN_DATA) != 0;
+        }
+
+        if (mPublicKey.getAlgorithm() == PGPPublicKey.RSA_GENERAL
+                || mPublicKey.getAlgorithm() == PGPPublicKey.RSA_SIGN
+                || mPublicKey.getAlgorithm() == PGPPublicKey.ECDSA) {
             return true;
         }
 
-        return (getKeyUsage() & KeyFlags.SIGN_DATA) != 0;
+        return false;
+    }
+
+    public boolean canEncrypt() {
+        // if key flags subpacket is available, honor it!
+        if (getKeyUsage() != null) {
+            return (getKeyUsage() & (KeyFlags.ENCRYPT_COMMS | KeyFlags.ENCRYPT_STORAGE)) != 0;
+        }
+
+        // RSA_GENERAL, RSA_ENCRYPT, ELGAMAL_ENCRYPT, ELGAMAL_GENERAL, ECDH
+        if (mPublicKey.isEncryptionKey()) {
+            return true;
+        }
+
+        return false;
+    }
+
+    public boolean canAuthenticate() {
+        // if key flags subpacket is available, honor it!
+        if (getKeyUsage() != null) {
+            return (getKeyUsage() & KeyFlags.AUTHENTICATION) != 0;
+        }
+
+        return false;
     }
 
     public byte[] getFingerprint() {