Refactor OpenSSL usage into a platform-specific file to allow other crypto backends

src/PlatformCrypto.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <stdbool.h>
+
+// Hide the real OpenSSL definition from other code
+typedef struct evp_cipher_ctx_st EVP_CIPHER_CTX;
+
+typedef struct _PLT_CRYPTO_CONTEXT {
+    bool initialized; // Used for CBC only
+    EVP_CIPHER_CTX* ctx;
+} PLT_CRYPTO_CONTEXT, *PPLT_CRYPTO_CONTEXT;
+
+#define ROUND_TO_PKCS7_PADDED_LEN(x) ((((x) + 15) / 16) * 16)
+
+PPLT_CRYPTO_CONTEXT PltCreateCryptoContext();
+void PltDestroyCryptoContext(PPLT_CRYPTO_CONTEXT ctx);
+
+#define ALGORITHM_AES_CBC 1
+#define ALGORITHM_AES_GCM 2
+
+bool PltEncryptMessage(PPLT_CRYPTO_CONTEXT ctx, int algorithm,
+                       unsigned char* key, int keyLength,
+                       unsigned char* iv, int ivLength,
+                       unsigned char* tag, int tagLength,
+                       unsigned char* inputData, int inputDataLength,
+                       unsigned char* outputData, int* outputDataLength);
+
+bool PltDecryptMessage(PPLT_CRYPTO_CONTEXT ctx, int algorithm,
+                       unsigned char* key, int keyLength,
+                       unsigned char* iv, int ivLength,
+                       unsigned char* tag, int tagLength,
+                       unsigned char* inputData, int inputDataLength,
+                       unsigned char* outputData, int* outputDataLength);
+
+void PltGenerateRandomData(unsigned char* data, int length);