Initial commit to new repository

src/AxKeyEncryptor/CryptoHelper.cs

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+using System.Security.Cryptography;
+using System.Text;
+
+namespace AxKeyEncryptor;
+
+/// <summary>
+/// 앱 공용 키(Portable) 암호화/복호화 — CryptoService.cs와 동일한 로직.
+/// </summary>
+internal static class CryptoHelper
+{
+    private static readonly byte[] AppSeed =
+    {
+        // "AX-Commander-Key-0104-sj.baeck" + 2-byte pad
+        0x41, 0x58, 0x2D, 0x43, 0x6F, 0x6D, 0x6D, 0x61,
+        0x6E, 0x64, 0x65, 0x72, 0x2D, 0x4B, 0x65, 0x79,
+        0x2D, 0x30, 0x31, 0x30, 0x34, 0x2D, 0x73, 0x6A,
+        0x2E, 0x62, 0x61, 0x65, 0x63, 0x6B, 0xA7, 0x5C
+    };
+
+    private static readonly byte[] AppSalt =
+    {
+        0x58, 0x43, 0x4D, 0x44, 0x53, 0x61, 0x6C, 0x74,
+        0x9E, 0x27, 0xC1, 0x4A, 0xB3, 0x06, 0x7F, 0xD8
+    };
+
+    private static byte[]? _appKey;
+
+    private static byte[] GetAppKey()
+    {
+        if (_appKey != null) return _appKey;
+        using var pbkdf2 = new Rfc2898DeriveBytes(AppSeed, AppSalt, 100_000, HashAlgorithmName.SHA256);
+        _appKey = pbkdf2.GetBytes(32);
+        return _appKey;
+    }
+
+    public static string Encrypt(string plainText)
+    {
+        if (string.IsNullOrEmpty(plainText)) return "";
+        var key = GetAppKey();
+        using var aes = Aes.Create();
+        aes.Key = key;
+        aes.Mode = CipherMode.CBC;
+        aes.Padding = PaddingMode.PKCS7;
+        aes.GenerateIV();
+
+        using var enc = aes.CreateEncryptor();
+        var plainBytes = Encoding.UTF8.GetBytes(plainText);
+        var cipher = enc.TransformFinalBlock(plainBytes, 0, plainBytes.Length);
+
+        var result = new byte[16 + cipher.Length];
+        Buffer.BlockCopy(aes.IV, 0, result, 0, 16);
+        Buffer.BlockCopy(cipher, 0, result, 16, cipher.Length);
+        return Convert.ToBase64String(result);
+    }
+
+    public static (bool Success, string Result) Decrypt(string base64)
+    {
+        if (string.IsNullOrEmpty(base64)) return (false, "입력이 비어 있습니다.");
+        try
+        {
+            var raw = Convert.FromBase64String(base64);
+            if (raw.Length < 17) return (false, "데이터가 너무 짧습니다.");
+
+            var key = GetAppKey();
+            var iv = new byte[16];
+            Buffer.BlockCopy(raw, 0, iv, 0, 16);
+            var cipher = new byte[raw.Length - 16];
+            Buffer.BlockCopy(raw, 16, cipher, 0, cipher.Length);
+
+            using var aes = Aes.Create();
+            aes.Key = key;
+            aes.IV = iv;
+            aes.Mode = CipherMode.CBC;
+            aes.Padding = PaddingMode.PKCS7;
+
+            using var dec = aes.CreateDecryptor();
+            var plain = dec.TransformFinalBlock(cipher, 0, cipher.Length);
+            return (true, Encoding.UTF8.GetString(plain));
+        }
+        catch (Exception ex)
+        {
+            return (false, $"복호화 오류: {ex.Message}");
+        }
+    }
+}