fix cv25519 encryption key generation

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

@@ -269,9 +269,14 @@ public class PgpKeyOperation {
                         return null;
                     }
                     progress(R.string.progress_generating_ecdh, 30);
+                    if (add.getCurve() == Curve.CV25519) {
+                        keyGen = KeyPairGenerator.getInstance("X25519");
+                        keyGen.initialize(255);
+                    } else {
                         ECGenParameterSpec ecParamSpec = getEccParameterSpec(add.getCurve());
                         keyGen = KeyPairGenerator.getInstance("ECDH", Constants.BOUNCY_CASTLE_PROVIDER_NAME);
                         keyGen.initialize(ecParamSpec, new SecureRandom());
+                    }
 
                     algorithm = PGPPublicKey.ECDH;
                     break;

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/SaveKeyringParcel.java

@@ -324,7 +324,7 @@ public abstract class SaveKeyringParcel implements Parcelable {
     // All curves defined in the standard
     // http://www.bouncycastle.org/wiki/pages/viewpage.action?pageId=362269
     public enum Curve {
-        NIST_P256, NIST_P384, NIST_P521,
+        NIST_P256, NIST_P384, NIST_P521, CV25519
 
         // these are supported by gpg, but they are not in rfc6637 and not supported by BouncyCastle yet
         // (adding support would be trivial though -> JcaPGPKeyConverter.java:190)

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/dialog/AddSubkeyDialogFragment.java

@@ -262,6 +262,10 @@ public class AddSubkeyDialogFragment extends DialogFragment {
                             curve = Curve.NIST_P521;
                             break;
                         }
+                        case EDDSA: {
+                            curve = Curve.CV25519;
+                            break;
+                        }
                     }
 
                     // set algorithm
@@ -283,9 +287,13 @@ public class AddSubkeyDialogFragment extends DialogFragment {
                             break;
                         }
                         case EDDSA: {
+                            if(mUsageEncrypt.isChecked()) {
+                                algorithm = Algorithm.ECDH;
+                            } else {
                                 algorithm = Algorithm.EDDSA;
                             }
                         }
+                    }
 
                     // set flags
                     int flags = 0;

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/util/KeyFormattingUtils.java

@@ -188,6 +188,8 @@ public class KeyFormattingUtils {
                 return "NIST P-384";
             case NIST_P521:
                 return "NIST P-521";
+            case CV25519:
+                return "Curve25519";
 
             /* see SaveKeyringParcel
             case BRAINPOOL_P256: