[Kernel] Add XeCryptRc4* funcs

src/xenia/kernel/xboxkrnl/xboxkrnl_crypt.cc

@@ -25,11 +25,62 @@ namespace xe {
 namespace kernel {
 namespace xboxkrnl {
 
+typedef struct {
+  uint8_t S[256];  // 0x0
+  uint8_t i;       // 0x100
+  uint8_t j;       // 0x101
+} XECRYPT_RC4_STATE;
+static_assert_size(XECRYPT_RC4_STATE, 0x102);
+
+void XeCryptRc4Key(pointer_t<XECRYPT_RC4_STATE> rc4_ctx, lpvoid_t key,
+                   dword_t key_size) {
+  // Setup RC4 state
+  rc4_ctx->i = rc4_ctx->j = 0;
+  for (uint32_t x = 0; x < 0x100; x++) {
+    rc4_ctx->S[x] = (uint8_t)x;
+  }
+
+  uint32_t idx = 0;
+  for (uint32_t x = 0; x < 0x100; x++) {
+    idx = (idx + rc4_ctx->S[x] + key[x % 0x10]) % 0x100;
+    uint8_t temp = rc4_ctx->S[idx];
+    rc4_ctx->S[idx] = rc4_ctx->S[x];
+    rc4_ctx->S[x] = temp;
+  }
+}
+DECLARE_XBOXKRNL_EXPORT1(XeCryptRc4Key, kNone, kImplemented);
+
+void XeCryptRc4Ecb(pointer_t<XECRYPT_RC4_STATE> rc4_ctx, lpvoid_t data,
+                   dword_t size) {
+  // Crypt data
+  for (uint32_t idx = 0; idx < size; idx++) {
+    rc4_ctx->i = (rc4_ctx->i + 1) % 0x100;
+    rc4_ctx->j = (rc4_ctx->j + rc4_ctx->S[rc4_ctx->i]) % 0x100;
+    uint8_t temp = rc4_ctx->S[rc4_ctx->i];
+    rc4_ctx->S[rc4_ctx->i] = rc4_ctx->S[rc4_ctx->j];
+    rc4_ctx->S[rc4_ctx->j] = temp;
+
+    uint8_t a = data[idx];
+    uint8_t b =
+        rc4_ctx->S[(rc4_ctx->S[rc4_ctx->i] + rc4_ctx->S[rc4_ctx->j]) % 0x100];
+    data[idx] = (uint8_t)(a ^ b);
+  }
+}
+DECLARE_XBOXKRNL_EXPORT1(XeCryptRc4Ecb, kNone, kImplemented);
+
+void XeCryptRc4(lpvoid_t key, dword_t key_size, lpvoid_t data, dword_t size) {
+  XECRYPT_RC4_STATE rc4_ctx;
+  XeCryptRc4Key(&rc4_ctx, key, key_size);
+  XeCryptRc4Ecb(&rc4_ctx, data, size);
+}
+DECLARE_XBOXKRNL_EXPORT1(XeCryptRc4, kNone, kImplemented);
+
 typedef struct {
   xe::be<uint32_t> count;     // 0x0
   xe::be<uint32_t> state[5];  // 0x4
   uint8_t buffer[64];         // 0x18
 } XECRYPT_SHA_STATE;
+static_assert_size(XECRYPT_SHA_STATE, 0x58);
 
 void InitSha1(sha1::SHA1* sha, const XECRYPT_SHA_STATE* state) {
   uint32_t digest[5];