Curve 25519: Support use via Android Keystore provider (part 1)

Ensure that the user gets an accurate error message when they try to
generate Curve 25519 keys according to JEP 324
(https://openjdk.java.net/jeps/324).

Android Keystore requires every key to have a name, so it is not
possible to generate a key using NamedParameterSpec only (with a
KeyPairGenerator).

Support this and throw an exception to the caller indicating how they
_can_ generate keys with this curve.

Bug: 222440855
Bug: 195309719
Bug: 194359292
Test: atest android.keystore.cts.KeyFactoryTest android.keystore.cts.Curve25519Test
Test: atest CtsLibcoreTestCases:libcore.java.security.ProviderTest
Change-Id: I5aa163f177507906c6482d079eb6cb55d93accf7

keystore/java/android/security/keystore2/AndroidKeyStoreKeyPairGeneratorSpi.java

@@ -108,6 +108,16 @@ public abstract class AndroidKeyStoreKeyPairGeneratorSpi extends KeyPairGenerato
         }
     }
 
+    /**
+     * XDH represents Curve 25519 providers.
+     */
+    public static class XDH extends AndroidKeyStoreKeyPairGeneratorSpi {
+        // XDH is treated as EC.
+        public XDH() {
+            super(KeymasterDefs.KM_ALGORITHM_EC);
+        }
+    }
+
     /*
      * These must be kept in sync with system/security/keystore/defaults.h
      */
@@ -242,6 +252,23 @@ public abstract class AndroidKeyStoreKeyPairGeneratorSpi extends KeyPairGenerato
                 } catch (NullPointerException | IllegalArgumentException e) {
                     throw new InvalidAlgorithmParameterException(e);
                 }
+            } else if (params instanceof NamedParameterSpec) {
+                NamedParameterSpec namedSpec = (NamedParameterSpec) params;
+                // Android Keystore cannot support initialization from a NamedParameterSpec
+                // because an alias for the key is needed (a KeyGenParameterSpec cannot be
+                // constructed).
+                if (namedSpec.getName().equalsIgnoreCase(NamedParameterSpec.X25519.getName())
+                        || namedSpec.getName().equalsIgnoreCase(
+                        NamedParameterSpec.ED25519.getName())) {
+                    throw new IllegalArgumentException(
+                            "This KeyPairGenerator cannot be initialized using NamedParameterSpec."
+                                    + " use " + KeyGenParameterSpec.class.getName() + " or "
+                                    + KeyPairGeneratorSpec.class.getName());
+                } else {
+                    throw new InvalidAlgorithmParameterException(
+                            "Unsupported algorithm specified via NamedParameterSpec: "
+                            + namedSpec.getName());
+                }
             } else {
                 throw new InvalidAlgorithmParameterException(
                         "Unsupported params class: " + params.getClass().getName()

keystore/java/android/security/keystore2/AndroidKeyStoreProvider.java

@@ -83,10 +83,12 @@ public class AndroidKeyStoreProvider extends Provider {
         // java.security.KeyPairGenerator
         put("KeyPairGenerator.EC", PACKAGE_NAME + ".AndroidKeyStoreKeyPairGeneratorSpi$EC");
         put("KeyPairGenerator.RSA", PACKAGE_NAME +  ".AndroidKeyStoreKeyPairGeneratorSpi$RSA");
+        put("KeyPairGenerator.XDH", PACKAGE_NAME +  ".AndroidKeyStoreKeyPairGeneratorSpi$XDH");
 
         // java.security.KeyFactory
         putKeyFactoryImpl("EC");
         putKeyFactoryImpl("RSA");
+        putKeyFactoryImpl("XDH");
 
         // javax.crypto.KeyGenerator
         put("KeyGenerator.AES", PACKAGE_NAME + ".AndroidKeyStoreKeyGeneratorSpi$AES");