Add more curve25519 operations

library/src/main/cpp/curve25519.cpp

@@ -24,4 +24,15 @@ Java_network_loki_messenger_libsession_1util_Curve25519_pubKeyFromED25519(JNIEnv
         auto pk = session::curve25519::to_curve25519_pubkey(jni_utils::JavaByteArrayRef(env, ed25519_public_key).get());
         return util::bytes_from_span(env, pk);
     });
+}
+
+extern "C"
+JNIEXPORT jobject JNICALL
+Java_network_loki_messenger_libsession_1util_Curve25519_generateKeyPair(JNIEnv *env, jobject thiz) {
+    return jni_utils::run_catching_cxx_exception_or_throws<jobject>(env, [=] {
+        auto [sk, pk] = session::curve25519::curve25519_key_pair();
+        return jni_utils::new_key_pair(env,
+                                       util::bytes_from_span(env, sk),
+                                        util::bytes_from_span(env, pk));
+    });
 }

library/src/main/cpp/encryption.cpp

@@ -4,6 +4,8 @@
 
 #include "jni_utils.h"
 
+#include <sodium.h>
+
 using jni_utils::JavaByteArrayRef;
 
 extern "C"
@@ -125,4 +127,33 @@ Java_network_loki_messenger_libsession_1util_SessionEncrypt_decryptOnsResponse(J
 
         return util::jstringFromOptional(env, data);
     });
+}
+
+extern "C"
+JNIEXPORT jbyteArray JNICALL
+Java_network_loki_messenger_libsession_1util_SessionEncrypt_calculateECHDAgreement(JNIEnv *env,
+                                                                                   jobject thiz,
+                                                                                   jbyteArray x25519_pub_key,
+                                                                                   jbyteArray x25519_priv_key) {
+    return jni_utils::run_catching_cxx_exception_or_throws<jbyteArray>(env, [=] {
+        JavaByteArrayRef sk(env, x25519_priv_key);
+        JavaByteArrayRef pk(env, x25519_pub_key);
+
+        if (sk.get().size() != crypto_scalarmult_SCALARBYTES) {
+            throw std::invalid_argument{"Invalid x25519_priv_key: expected 32 bytes"};
+        }
+
+        if (pk.get().size() != crypto_scalarmult_BYTES) {
+            throw std::invalid_argument{"Invalid x25519_pub_key: expected 32 bytes"};
+        }
+
+        std::array<unsigned char, crypto_scalarmult_BYTES> shared_secret {0};
+        if (crypto_scalarmult(shared_secret.data(),sk.get().data(), pk.get().data()) != 0) {
+            throw std::runtime_error{"An error occurred while attempting to calculate the shared "
+                                      "secret; is the key valid?"};
+        }
+
+        return util::bytes_from_span(env, shared_secret);
+    });
+
 }

library/src/main/java/network/loki/messenger/libsession_util/Curve25519.kt

@@ -17,4 +17,6 @@ object Curve25519 : LibSessionUtilCApi() {
     external fun pubKeyFromED25519(
         ed25519PublicKey: ByteArray,
     ): ByteArray
+
+    external fun generateKeyPair(): KeyPair
 }

library/src/main/java/network/loki/messenger/libsession_util/SessionEncrypt.kt

@@ -77,4 +77,9 @@ object SessionEncrypt : LibSessionUtilCApi() {
         ciphertext: ByteArray,
         nonce: ByteArray?,
     ): SessionId
+
+    external fun calculateECHDAgreement(
+        x25519PubKey: ByteArray,
+        x25519PrivKey: ByteArray,
+    ): ByteArray
 }