Upgrade handshake protocol to new key agreement method.

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/CryptoComponent.java

@@ -54,6 +54,38 @@ public interface CryptoComponent {
 			KeyPair ourKeyPair, byte[]... inputs)
 			throws GeneralSecurityException;
 
+	/**
+	 * Derives a shared secret from two static and two ephemeral key pairs.
+	 * <p>
+	 * Do not use this method for new protocols. The shared secret can be
+	 * re-derived using the ephemeral public keys and both static private
+	 * keys, so keys derived from the shared secret should not be used if
+	 * forward secrecy is required. Use {@link #deriveSharedSecret(String,
+	 * PublicKey, PublicKey, KeyPair, KeyPair, boolean, byte[]...)} instead.
+	 * <p>
+	 * TODO: Remove this after a reasonable migration period (added 2023-03-10).
+	 * <p>
+	 *
+	 * @param label A namespaced label indicating the purpose of this shared
+	 * secret, to prevent it from being repurposed or colliding with a shared
+	 * secret derived for another purpose
+	 * @param theirStaticPublicKey The static public key of the remote party
+	 * @param theirEphemeralPublicKey The ephemeral public key of the remote
+	 * party
+	 * @param ourStaticKeyPair The static key pair of the local party
+	 * @param ourEphemeralKeyPair The ephemeral key pair of the local party
+	 * @param alice True if the local party is Alice
+	 * @param inputs Additional inputs that will be included in the
+	 * derivation of the shared secret
+	 * @return The shared secret
+	 */
+	@Deprecated
+	SecretKey deriveSharedSecretBadly(String label,
+			PublicKey theirStaticPublicKey, PublicKey theirEphemeralPublicKey,
+			KeyPair ourStaticKeyPair, KeyPair ourEphemeralKeyPair,
+			boolean alice, byte[]... inputs)
+			throws GeneralSecurityException;
+
 	/**
 	 * Derives a shared secret from two static and two ephemeral key pairs.
 	 *