1 files changed, 35 insertions, 0 deletions
diff --git a/protocols/WhatsAppWeb/src/utils.cpp b/protocols/WhatsAppWeb/src/utils.cpp
index 49ece0557a..bc35b6ef5f 100644
--- a/protocols/WhatsAppWeb/src/utils.cpp
+++ b/protocols/WhatsAppWeb/src/utils.cpp
@@ -34,3 +34,38 @@ WAUser* WhatsAppProto::AddUser(const char *szId, bool bTemporary)
 	m_arUsers.insert(pUser);
 	return pUser;
 }
+
+/////////////////////////////////////////////////////////////////////////////////////////
+
+bool WhatsAppProto::decryptBinaryMessage(size_t cbSize, const void *buf, MBinBuffer &res)
+{
+	if (cbSize <= 32)
+		return false;
+
+	// validate message first
+	{
+		unsigned int md_len = 32;
+		BYTE md[32];
+		HMAC(EVP_sha256(), mac_key.data(), (int)mac_key.length(), (unsigned char *)buf+32, (int)cbSize-32, md, &md_len);
+		if (memcmp(buf, md, sizeof(md))) {
+			debugLogA("Message cannot be decrypted, check your keys");
+			return false;
+		}
+	}
+	
+	// okay, let's decrypt this thing
+	{
+		BYTE iv[16];
+		memcpy(iv, (char*)buf + 32, sizeof(iv));
+		res.assign((char*)buf + 48, cbSize - 48);
+		res.append((char*)mac_key.data(), 32); // reserve 32 more bytes for temp data
+
+		int dec_len = 0, final_len = 0;
+		EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
+		EVP_DecryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, (BYTE*)enc_key.data(), iv);
+		EVP_DecryptUpdate(ctx, (BYTE*)res.data(), &dec_len, (BYTE*)buf + 48, (int)cbSize - 48);
+		EVP_DecryptFinal_ex(ctx, (BYTE*)res.data() + dec_len, &final_len);
+		EVP_CIPHER_CTX_free(ctx);
+	}
+	return true;
+}