Initial commit

NHSE.Core/Encryption/Encryption.cs

@@ -0,0 +1,85 @@
+using System;
+
+namespace NHSE.Core
+{
+    public static class Encryption
+    {
+        private static byte[] GetParam(uint[] data, in int index)
+        {
+            var sead = new SEADRandom(data[data[index] & 0x7F]);
+            var prms = data[data[index + 1] & 0x7F] & 0x7F;
+
+            var rndRollCount = (prms & 0xF) + 1;
+            for (var i = 0; i < rndRollCount; i++)
+                sead.GetU64();
+
+            var result = new byte[0x10];
+            for (var i = 0; i < result.Length; i++)
+                result[i] = (byte)(sead.GetU32() >> 24);
+
+            return result;
+        }
+
+        /// <summary>
+        /// Decrypts the <see cref="encData"/> using the <see cref="headerData"/>.
+        /// </summary>
+        /// <param name="headerData">Header Data</param>
+        /// <param name="encData">Encrypted SaveData</param>
+        /// <returns>Decrypted SaveData</returns>
+        public static byte[] Decrypt(byte[] headerData, byte[] encData)
+        {
+            // First 256 bytes go unused
+            var importantData = new uint[0x80];
+            Buffer.BlockCopy(headerData, 0x100, importantData, 0, 0x200);
+
+            // Set up Key
+            var key = GetParam(importantData, 0);
+
+            // Set up counter
+            var counter = GetParam(importantData, 2);
+
+            // Do the AES
+            using var aesCtr = new Aes128CounterMode(counter);
+            var transform = aesCtr.CreateDecryptor(key, counter);
+            var decData = new byte[encData.Length];
+
+            transform.TransformBlock(encData, 0, encData.Length, decData, 0);
+            return decData;
+        }
+
+        private static CryptoFile GenerateHeaderFile(uint seed, byte[] versionData)
+        {
+            // Generate 128 Random uints which will be used for params
+            var random = new SEADRandom(seed);
+            var encryptData = new uint[128];
+            for (var i = 0; i < encryptData.Length; i++)
+                encryptData[i] = random.GetU32();
+
+            var headerData = new byte[0x300];
+            Buffer.BlockCopy(versionData, 0, headerData, 0, 0x100);
+            Buffer.BlockCopy(encryptData, 0, headerData, 0x100, 0x200);
+            return new CryptoFile(headerData, GetParam(encryptData, 0), GetParam(encryptData, 2));
+        }
+
+        /// <summary>
+        /// Encrypts the <see cref="data"/> (savedata) using the provided <see cref="seed"/>.
+        /// </summary>
+        /// <param name="data">SaveData to encrypt</param>
+        /// <param name="seed">Seed to encrypt with</param>
+        /// <param name="versionData">Version data to encrypt with</param>
+        /// <returns>Encrypted SaveData, and associated headerData</returns>
+        public static EncryptedSaveFile Encrypt(byte[] data, uint seed, byte[] versionData)
+        {
+            // Generate header file and get key and counter
+            var header = GenerateHeaderFile(seed, versionData);
+
+            // Encrypt file
+            using var aesCtr = new Aes128CounterMode(header.Ctr);
+            var transform = aesCtr.CreateEncryptor(header.Key, header.Ctr);
+            var encData = new byte[data.Length];
+            transform.TransformBlock(data, 0, data.Length, encData, 0);
+
+            return new EncryptedSaveFile(encData, header.Data);
+        }
+    }
+}