Initial implementation of location sharing

Signed-off-by: zyphlar <zyphlar@gmail.com>

libs/location_sharing/crypto_util.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "location_sharing_types.hpp"
+
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace location_sharing
+{
+namespace crypto
+{
+
+// AES-256-GCM encryption parameters
+constexpr size_t kAesKeySize = 32;      // 256 bits
+constexpr size_t kGcmIvSize = 12;       // 96 bits (recommended for GCM)
+constexpr size_t kGcmAuthTagSize = 16;  // 128 bits
+
+// Encrypt data using AES-256-GCM
+// key: base64-encoded 32-byte key
+// plaintext: data to encrypt
+// Returns: encrypted payload with IV and auth tag, or nullopt on failure
+std::optional<EncryptedPayload> EncryptAes256Gcm(
+    std::string const & key,
+    std::string const & plaintext);
+
+// Decrypt data using AES-256-GCM
+// key: base64-encoded 32-byte key
+// payload: encrypted payload with IV and auth tag
+// Returns: decrypted plaintext, or nullopt on failure/auth failure
+std::optional<std::string> DecryptAes256Gcm(
+    std::string const & key,
+    EncryptedPayload const & payload);
+
+// Generate a random IV (initialization vector)
+std::vector<uint8_t> GenerateRandomIV();
+
+// Generate a random AES-256 key (32 bytes)
+std::vector<uint8_t> GenerateRandomKey();
+
+}  // namespace crypto
+}  // namespace location_sharing