I have sinned but it feels good

native/src/main/c/jni_cipher_openssl.c

@@ -0,0 +1,62 @@
+#include <jni.h>
+#include <stdlib.h>
+#include <string.h>
+#include <openssl/evp.h>
+#include "jni_util.h"
+
+typedef unsigned char byte;
+
+JNIEXPORT jlong JNICALL
+Java_com_velocitypowered_natives_encryption_OpenSslCipherImpl_init(JNIEnv *env,
+    jclass clazz,
+    jbyteArray key,
+    jboolean encrypt)
+{
+    jsize keyLen = (*env)->GetArrayLength(env, key);
+    if (keyLen != 16) {
+        throwException(env, "java/lang/IllegalArgumentException", "cipher not 16 bytes");
+        return 0;
+    }
+
+    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+    if (ctx == NULL) {
+        throwException(env, "java/lang/OutOfMemoryError", "allocate cipher");
+        return 0;
+    }
+
+    // Since we know the array size is always bounded, we can just use Get<Primitive>ArrayRegion
+    // and save ourselves some error-checking headaches.
+    jbyte keyBytes[16];
+    (*env)->GetByteArrayRegion(env, key, 0, keyLen, (jbyte*) keyBytes);
+    if ((*env)->ExceptionCheck(env)) {
+        return 0;
+    }
+
+    int result = EVP_CipherInit(ctx, EVP_aes_128_cfb8(), (byte*) keyBytes, (byte*) keyBytes,
+        encrypt);
+    if (result != 1) {
+        EVP_CIPHER_CTX_free(ctx);
+        throwException(env, "java/security/GeneralSecurityException", "openssl initialize cipher");
+        return 0;
+    }
+    return (jlong) ctx;
+}
+
+JNIEXPORT void JNICALL
+Java_com_velocitypowered_natives_encryption_OpenSslCipherImpl_free(JNIEnv *env,
+    jclass clazz,
+    jlong ptr)
+{
+    EVP_CIPHER_CTX_free((EVP_CIPHER_CTX *) ptr);
+}
+
+JNIEXPORT void JNICALL
+Java_com_velocitypowered_natives_encryption_OpenSslCipherImpl_process(JNIEnv *env,
+    jclass clazz,
+    jlong ptr,
+    jlong source,
+    jint len,
+    jlong dest)
+{
+    EVP_CipherUpdate((EVP_CIPHER_CTX*) ptr, (byte*) dest, &len, (byte*) source, len);
+}