diff --git a/stratosphere/spl/source/spl_api_impl.cpp b/stratosphere/spl/source/spl_api_impl.cpp
index d21497229..84e5a921c 100644
--- a/stratosphere/spl/source/spl_api_impl.cpp
+++ b/stratosphere/spl/source/spl_api_impl.cpp
@@ -14,8 +14,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include "spl_api_impl.hpp"
-
 #include "spl_ctr_drbg.hpp"
+#include "spl_key_slot_cache.hpp"
 
 namespace ams::spl::impl {
 
@@ -34,21 +34,161 @@ namespace ams::spl::impl {
 
         constexpr size_t WorkBufferSizeMax = 0x800;
 
-        constexpr size_t MaxAesKeyslots = 6;
-        constexpr size_t MaxAesKeyslotsDeprecated = 4;
+        constexpr s32 MaxPhysicalAesKeyslots = 6;
+        constexpr s32 MaxPhysicalAesKeyslotsDeprecated = 4;
 
-        /* Max Keyslots helper. */
-        inline size_t GetMaxKeyslots() {
-            return (hos::GetVersion() >= hos::Version_6_0_0) ? MaxAesKeyslots : MaxAesKeyslotsDeprecated;
+        constexpr s32 MaxVirtualAesKeyslots = 9;
+
+        /* Keyslot management. */
+        KeySlotCache g_keyslot_cache;
+        std::optional<KeySlotCacheEntry> g_keyslot_cache_entry[MaxPhysicalAesKeyslots];
+
+        inline s32 GetMaxPhysicalKeyslots() {
+            return (hos::GetVersion() >= hos::Version_6_0_0) ? MaxPhysicalAesKeyslots : MaxPhysicalAesKeyslotsDeprecated;
+        }
+
+        constexpr s32 VirtualKeySlotMin = 16;
+        constexpr s32 VirtualKeySlotMax = VirtualKeySlotMin + MaxVirtualAesKeyslots - 1;
+
+        constexpr inline bool IsVirtualKeySlot(s32 keyslot) {
+            return VirtualKeySlotMin <= keyslot && keyslot <= VirtualKeySlotMax;
+        }
+
+        inline bool IsPhysicalKeySlot(s32 keyslot) {
+            return keyslot < GetMaxPhysicalKeyslots();
+        }
+
+        constexpr inline s32 GetVirtualKeySlotIndex(s32 keyslot) {
+            AMS_ASSERT(IsVirtualKeySlot(keyslot));
+            return keyslot - VirtualKeySlotMin;
+        }
+
+        constexpr inline s32 MakeVirtualKeySlot(s32 index) {
+            const s32 virt_slot = index + VirtualKeySlotMin;
+            AMS_ASSERT(IsVirtualKeySlot(virt_slot));
+            return virt_slot;
+        }
+
+        void InitializeKeySlotCache() {
+            for (s32 i = 0; i < MaxPhysicalAesKeyslots; i++) {
+                g_keyslot_cache_entry[i].emplace(i);
+                g_keyslot_cache.AddEntry(std::addressof(g_keyslot_cache_entry[i].value()));
+            }
+        }
+
+        enum class KeySlotContentType {
+            None      = 0,
+            AesKey    = 1,
+            TitleKey  = 2,
+        };
+
+        struct KeySlotContents {
+            KeySlotContentType type;
+            union {
+                struct {
+                    AccessKey access_key;
+                    KeySource key_source;
+                } aes_key;
+                struct {
+                    AccessKey access_key;
+                } title_key;
+            };
+        };
+
+        const void *g_keyslot_owners[MaxVirtualAesKeyslots];
+        KeySlotContents g_keyslot_contents[MaxVirtualAesKeyslots];
+        KeySlotContents g_physical_keyslot_contents_for_backwards_compatibility[MaxPhysicalAesKeyslots];
+
+        void ClearPhysicalKeyslot(s32 keyslot) {
+            AMS_ASSERT(IsPhysicalKeySlot(keyslot));
+
+            AccessKey access_key = {};
+            KeySource key_source = {};
+            smc::LoadAesKey(keyslot, access_key, key_source);
+        }
+
+        s32 GetPhysicalKeySlot(s32 keyslot, bool load) {
+            s32 phys_slot = -1;
+            KeySlotContents *contents = nullptr;
+
+            if (hos::GetVersion() == hos::Version_1_0_0 && IsPhysicalKeySlot(keyslot)) {
+                /* On 1.0.0, we allow the use of physical keyslots. */
+                phys_slot = keyslot;
+                contents = std::addressof(g_physical_keyslot_contents_for_backwards_compatibility[phys_slot]);
+
+                /* If the physical slot is already loaded, we're good. */
+                if (g_keyslot_cache.FindPhysical(phys_slot)) {
+                    return phys_slot;
+                }
+            } else {
+                /* This should be a virtual keyslot. */
+                AMS_ASSERT(IsVirtualKeySlot(keyslot));
+
+                /* Try to find a physical slot in the cache. */
+                if (g_keyslot_cache.Find(std::addressof(phys_slot), keyslot)) {
+                    return phys_slot;
+                }
+
+                /* Allocate a physical slot. */
+                phys_slot = g_keyslot_cache.Allocate(keyslot);
+                contents = std::addressof(g_keyslot_contents[GetVirtualKeySlotIndex(keyslot)]);
+            }
+
+            /* Ensure the contents of the keyslot. */
+            if (load) {
+                switch (contents->type) {
+                    case KeySlotContentType::None:
+                        ClearPhysicalKeyslot(phys_slot);
+                        break;
+                    case KeySlotContentType::AesKey:
+                        R_ABORT_UNLESS(smc::ConvertResult(smc::LoadAesKey(phys_slot, contents->aes_key.access_key, contents->aes_key.key_source)));
+                        break;
+                    case KeySlotContentType::TitleKey:
+                        R_ABORT_UNLESS(smc::ConvertResult(smc::LoadTitleKey(phys_slot, contents->title_key.access_key)));
+                        break;
+                    AMS_UNREACHABLE_DEFAULT_CASE();
+                }
+            }
+
+            return phys_slot;
+        }
+
+        Result LoadVirtualAesKey(s32 keyslot, const AccessKey &access_key, const KeySource &key_source) {
+            /* Ensure we can load into the slot. */
+            const s32 phys_slot = GetPhysicalKeySlot(keyslot, false);
+            R_TRY(smc::ConvertResult(smc::LoadAesKey(phys_slot, access_key, key_source)));
+
+            /* Update our contents. */
+            const s32 index = GetVirtualKeySlotIndex(keyslot);
+
+            g_keyslot_contents[index].type               = KeySlotContentType::AesKey;
+            g_keyslot_contents[index].aes_key.access_key = access_key;
+            g_keyslot_contents[index].aes_key.key_source = key_source;
+
+            return ResultSuccess();
+        }
+
+        Result LoadVirtualTitleKey(s32 keyslot, const AccessKey &access_key) {
+            /* Ensure we can load into the slot. */
+            const s32 phys_slot = GetPhysicalKeySlot(keyslot, false);
+            R_TRY(smc::ConvertResult(smc::LoadTitleKey(phys_slot, access_key)));
+
+            /* Update our contents. */
+            const s32 index = GetVirtualKeySlotIndex(keyslot);
+
+            g_keyslot_contents[index].type                 = KeySlotContentType::TitleKey;
+            g_keyslot_contents[index].title_key.access_key = access_key;
+
+            return ResultSuccess();
         }
 
         /* Type definitions. */
         class ScopedAesKeyslot {
             private:
-                u32 slot;
+                s32 slot;
                 bool has_slot;
             public:
-                ScopedAesKeyslot() : slot(0), has_slot(false) {
+                ScopedAesKeyslot() : slot(-1), has_slot(false) {
                     /* ... */
                 }
                 ~ScopedAesKeyslot() {
@@ -57,7 +197,7 @@ namespace ams::spl::impl {
                     }
                 }
 
-                u32 GetKeyslot() const {
+                u32 GetKeySlot() const {
                     return this->slot;
                 }
 
@@ -106,7 +246,6 @@ namespace ams::spl::impl {
 
         os::Mutex g_async_op_lock(false);
 
-        const void *g_keyslot_owners[MaxAesKeyslots];
         BootReasonValue g_boot_reason;
         bool g_boot_reason_set;
 
@@ -201,14 +340,21 @@ namespace ams::spl::impl {
         }
 
         /* Internal Keyslot utility. */
-        Result ValidateAesKeyslot(u32 keyslot, const void *owner) {
-            R_UNLESS(keyslot < GetMaxKeyslots(), spl::ResultInvalidKeyslot());
-            R_UNLESS((g_keyslot_owners[keyslot] == owner || hos::GetVersion() == hos::Version_1_0_0), spl::ResultInvalidKeyslot());
+        Result ValidateAesKeyslot(s32 keyslot, const void *owner) {
+            /* Allow the use of physical keyslots on 1.0.0. */
+            if (hos::GetVersion() == hos::Version_1_0_0) {
+                R_SUCCEED_IF(IsPhysicalKeySlot(keyslot));
+            }
+
+            R_UNLESS(IsVirtualKeySlot(keyslot), spl::ResultInvalidKeyslot());
+
+            const s32 index = GetVirtualKeySlotIndex(keyslot);
+            R_UNLESS(g_keyslot_owners[index] == owner, spl::ResultInvalidKeyslot());
             return ResultSuccess();
         }
 
         /* Helper to do a single AES block decryption. */
-        smc::Result DecryptAesBlock(u32 keyslot, void *dst, const void *src) {
+        smc::Result DecryptAesBlock(s32 keyslot, void *dst, const void *src) {
             struct DecryptAesBlockLayout {
                 SeCryptContext crypt_ctx;
                 u8 in_block[AES_BLOCK_SIZE] __attribute__((aligned(AES_BLOCK_SIZE)));
@@ -230,7 +376,7 @@ namespace ams::spl::impl {
                 std::scoped_lock lk(g_async_op_lock);
                 smc::AsyncOperationKey op_key;
                 const IvCtr iv_ctr = {};
-                const u32 mode = smc::GetCryptAesMode(smc::CipherMode::CbcDecrypt, keyslot);
+                const u32 mode = smc::GetCryptAesMode(smc::CipherMode::CbcDecrypt, GetPhysicalKeySlot(keyslot, true));
                 const u32 dst_ll_addr = g_se_mapped_work_buffer_addr + offsetof(DecryptAesBlockLayout, crypt_ctx.out);
                 const u32 src_ll_addr = g_se_mapped_work_buffer_addr + offsetof(DecryptAesBlockLayout, crypt_ctx.in);
 
@@ -362,6 +508,8 @@ namespace ams::spl::impl {
         InitializeSeEvents();
         /* Initialize DAS for the SE. */
         InitializeDeviceAddressSpace();
+        /* Initialize the keyslot cache. */
+        InitializeKeySlotCache();
     }
 
     /* General. */
@@ -473,14 +621,12 @@ namespace ams::spl::impl {
         return smc::ConvertResult(smc::GenerateAesKek(out_access_key, key_source, generation, option));
     }
 
-    Result LoadAesKey(u32 keyslot, const void *owner, const AccessKey &access_key, const KeySource &key_source) {
+    Result LoadAesKey(s32 keyslot, const void *owner, const AccessKey &access_key, const KeySource &key_source) {
         R_TRY(ValidateAesKeyslot(keyslot, owner));
-        return smc::ConvertResult(smc::LoadAesKey(keyslot, access_key, key_source));
+        return LoadVirtualAesKey(keyslot, access_key, key_source);
     }
 
     Result GenerateAesKey(AesKey *out_key, const AccessKey &access_key, const KeySource &key_source) {
-        smc::Result smc_rc;
-
         static constexpr KeySource s_generate_aes_key_source = {
             .data = {0x89, 0x61, 0x5E, 0xE0, 0x5C, 0x31, 0xB6, 0x80, 0x5F, 0xE5, 0x8F, 0x3D, 0xA2, 0x4F, 0x7A, 0xA8}
         };
@@ -488,12 +634,9 @@ namespace ams::spl::impl {
         ScopedAesKeyslot keyslot_holder;
         R_TRY(keyslot_holder.Allocate());
 
-        smc_rc = smc::LoadAesKey(keyslot_holder.GetKeyslot(), access_key, s_generate_aes_key_source);
-        if (smc_rc == smc::Result::Success) {
-            smc_rc = DecryptAesBlock(keyslot_holder.GetKeyslot(), out_key, &key_source);
-        }
+        R_TRY(LoadVirtualAesKey(keyslot_holder.GetKeySlot(), access_key, s_generate_aes_key_source));
 
-        return smc::ConvertResult(smc_rc);
+        return smc::ConvertResult(DecryptAesBlock(keyslot_holder.GetKeySlot(), out_key, &key_source));
     }
 
     Result DecryptAesKey(AesKey *out_key, const KeySource &key_source, u32 generation, u32 option) {
@@ -507,7 +650,7 @@ namespace ams::spl::impl {
         return GenerateAesKey(out_key, access_key, key_source);
     }
 
-    Result CryptAesCtr(void *dst, size_t dst_size, u32 keyslot, const void *owner, const void *src, size_t src_size, const IvCtr &iv_ctr) {
+    Result CryptAesCtr(void *dst, size_t dst_size, s32 keyslot, const void *owner, const void *src, size_t src_size, const IvCtr &iv_ctr) {
         R_TRY(ValidateAesKeyslot(keyslot, owner));
 
         /* Succeed immediately if there's nothing to crypt. */
@@ -554,7 +697,7 @@ namespace ams::spl::impl {
         {
             std::scoped_lock lk(g_async_op_lock);
             smc::AsyncOperationKey op_key;
-            const u32 mode = smc::GetCryptAesMode(smc::CipherMode::Ctr, keyslot);
+            const u32 mode = smc::GetCryptAesMode(smc::CipherMode::Ctr, GetPhysicalKeySlot(keyslot, true));
             const u32 dst_ll_addr = g_se_mapped_work_buffer_addr + offsetof(SeCryptContext, out);
             const u32 src_ll_addr = g_se_mapped_work_buffer_addr + offsetof(SeCryptContext, in);
 
@@ -572,26 +715,22 @@ namespace ams::spl::impl {
         return ResultSuccess();
     }
 
-    Result ComputeCmac(Cmac *out_cmac, u32 keyslot, const void *owner, const void *data, size_t size) {
+    Result ComputeCmac(Cmac *out_cmac, s32 keyslot, const void *owner, const void *data, size_t size) {
         R_TRY(ValidateAesKeyslot(keyslot, owner));
 
         R_UNLESS(size <= WorkBufferSizeMax, spl::ResultInvalidSize());
 
         std::memcpy(g_work_buffer, data, size);
-        return smc::ConvertResult(smc::ComputeCmac(out_cmac, keyslot, g_work_buffer, size));
+        return smc::ConvertResult(smc::ComputeCmac(out_cmac, GetPhysicalKeySlot(keyslot, true), g_work_buffer, size));
     }
 
-    Result AllocateAesKeyslot(u32 *out_keyslot, const void *owner) {
-        if (hos::GetVersion() <= hos::Version_1_0_0) {
-            /* On 1.0.0, keyslots were kind of a wild west. */
-            *out_keyslot = 0;
-            return ResultSuccess();
-        }
-
-        for (size_t i = 0; i < GetMaxKeyslots(); i++) {
-            if (g_keyslot_owners[i] == 0) {
-                g_keyslot_owners[i] = owner;
-                *out_keyslot = static_cast<u32>(i);
+    Result AllocateAesKeyslot(s32 *out_keyslot, const void *owner) {
+        /* Find a virtual keyslot. */
+        for (s32 i = 0; i < MaxVirtualAesKeyslots; i++) {
+            if (g_keyslot_owners[i] == nullptr) {
+                g_keyslot_owners[i]   = owner;
+                g_keyslot_contents[i] = { .type = KeySlotContentType::None };
+                *out_keyslot = MakeVirtualKeySlot(i);
                 return ResultSuccess();
             }
         }
@@ -600,22 +739,24 @@ namespace ams::spl::impl {
         return spl::ResultOutOfKeyslots();
     }
 
-    Result FreeAesKeyslot(u32 keyslot, const void *owner) {
-        if (hos::GetVersion() <= hos::Version_1_0_0) {
-            /* On 1.0.0, keyslots were kind of a wild west. */
-            return ResultSuccess();
-        }
+    Result FreeAesKeyslot(s32 keyslot, const void *owner) {
+        /* Only virtual keyslots can be freed. */
+        R_UNLESS(IsVirtualKeySlot(keyslot), spl::ResultInvalidKeyslot());
 
+        /* Ensure the keyslot is owned. */
         R_TRY(ValidateAesKeyslot(keyslot, owner));
 
-        /* Clear the keyslot. */
-        {
-            AccessKey access_key = {};
-            KeySource key_source = {};
-
-            smc::LoadAesKey(keyslot, access_key, key_source);
+        /* Clear the physical keyslot, if we're cached. */
+        s32 phys_slot;
+        if (g_keyslot_cache.Release(std::addressof(phys_slot), keyslot)) {
+            ClearPhysicalKeyslot(phys_slot);
         }
-        g_keyslot_owners[keyslot] = nullptr;
+
+        /* Clear the virtual keyslot. */
+        const auto index               = GetVirtualKeySlotIndex(keyslot);
+        g_keyslot_owners[index]        = nullptr;
+        g_keyslot_contents[index].type = KeySlotContentType::None;
+
         os::SignalSystemEvent(std::addressof(g_se_keyslot_available_event));
         return ResultSuccess();
     }
@@ -701,7 +842,7 @@ namespace ams::spl::impl {
         return UnwrapEsRsaOaepWrappedKey(out_access_key, base, base_size, mod, mod_size, label_digest, label_digest_size, generation, smc::EsKeyType::ElicenseKey);
     }
 
-    Result LoadElicenseKey(u32 keyslot, const void *owner, const AccessKey &access_key) {
+    Result LoadElicenseKey(s32 keyslot, const void *owner, const AccessKey &access_key) {
         /* Right now, this is just literally the same function as LoadTitleKey in N's impl. */
         return LoadTitleKey(keyslot, owner, access_key);
     }
@@ -730,9 +871,9 @@ namespace ams::spl::impl {
         return smc::ConvertResult(smc::GenerateSpecificAesKey(out_key, key_source, generation, which));
     }
 
-    Result LoadTitleKey(u32 keyslot, const void *owner, const AccessKey &access_key) {
+    Result LoadTitleKey(s32 keyslot, const void *owner, const AccessKey &access_key) {
         R_TRY(ValidateAesKeyslot(keyslot, owner));
-        return smc::ConvertResult(smc::LoadTitleKey(keyslot, access_key));
+        return LoadVirtualTitleKey(keyslot, access_key);
     }
 
     Result GetPackage2Hash(void *dst, const size_t size) {
@@ -783,9 +924,9 @@ namespace ams::spl::impl {
 
     /* Helper. */
     Result FreeAesKeyslots(const void *owner) {
-        for (size_t i = 0; i < GetMaxKeyslots(); i++) {
-            if (g_keyslot_owners[i] == owner) {
-                FreeAesKeyslot(i, owner);
+        for (s32 slot = VirtualKeySlotMin; slot <= VirtualKeySlotMax; ++slot) {
+            if (g_keyslot_owners[GetVirtualKeySlotIndex(slot)] == owner) {
+                FreeAesKeyslot(slot, owner);
             }
         }
         return ResultSuccess();
diff --git a/stratosphere/spl/source/spl_api_impl.hpp b/stratosphere/spl/source/spl_api_impl.hpp
index 9422104ea..483f29e53 100644
--- a/stratosphere/spl/source/spl_api_impl.hpp
+++ b/stratosphere/spl/source/spl_api_impl.hpp
@@ -32,13 +32,13 @@ namespace ams::spl::impl {
 
     /* Crypto. */
     Result GenerateAesKek(AccessKey *out_access_key, const KeySource &key_source, u32 generation, u32 option);
-    Result LoadAesKey(u32 keyslot, const void *owner, const AccessKey &access_key, const KeySource &key_source);
+    Result LoadAesKey(s32 keyslot, const void *owner, const AccessKey &access_key, const KeySource &key_source);
     Result GenerateAesKey(AesKey *out_key, const AccessKey &access_key, const KeySource &key_source);
     Result DecryptAesKey(AesKey *out_key, const KeySource &key_source, u32 generation, u32 option);
-    Result CryptAesCtr(void *dst, size_t dst_size, u32 keyslot, const void *owner, const void *src, size_t src_size, const IvCtr &iv_ctr);
-    Result ComputeCmac(Cmac *out_cmac, u32 keyslot, const void *owner, const void *data, size_t size);
-    Result AllocateAesKeyslot(u32 *out_keyslot, const void *owner);
-    Result FreeAesKeyslot(u32 keyslot, const void *owner);
+    Result CryptAesCtr(void *dst, size_t dst_size, s32 keyslot, const void *owner, const void *src, size_t src_size, const IvCtr &iv_ctr);
+    Result ComputeCmac(Cmac *out_cmac, s32 keyslot, const void *owner, const void *data, size_t size);
+    Result AllocateAesKeyslot(s32 *out_keyslot, const void *owner);
+    Result FreeAesKeyslot(s32 keyslot, const void *owner);
 
     /* RSA. */
     Result DecryptRsaPrivateKey(void *dst, size_t dst_size, const void *src, size_t src_size, const AccessKey &access_key, const KeySource &key_source, u32 option);
@@ -54,13 +54,13 @@ namespace ams::spl::impl {
     Result ImportDrmKey(const void *src, size_t src_size, const AccessKey &access_key, const KeySource &key_source);
     Result DrmExpMod(void *out, size_t out_size, const void *base, size_t base_size, const void *mod, size_t mod_size);
     Result UnwrapElicenseKey(AccessKey *out_access_key, const void *base, size_t base_size, const void *mod, size_t mod_size, const void *label_digest, size_t label_digest_size, u32 generation);
-    Result LoadElicenseKey(u32 keyslot, const void *owner, const AccessKey &access_key);
+    Result LoadElicenseKey(s32 keyslot, const void *owner, const AccessKey &access_key);
 
     /* FS */
     Result ImportLotusKey(const void *src, size_t src_size, const AccessKey &access_key, const KeySource &key_source, u32 option);
     Result DecryptLotusMessage(u32 *out_size, void *dst, size_t dst_size, const void *base, size_t base_size, const void *mod, size_t mod_size, const void *label_digest, size_t label_digest_size);
     Result GenerateSpecificAesKey(AesKey *out_key, const KeySource &key_source, u32 generation, u32 which);
-    Result LoadTitleKey(u32 keyslot, const void *owner, const AccessKey &access_key);
+    Result LoadTitleKey(s32 keyslot, const void *owner, const AccessKey &access_key);
     Result GetPackage2Hash(void *dst, const size_t size);
 
     /* Manu. */
diff --git a/stratosphere/spl/source/spl_crypto_service.cpp b/stratosphere/spl/source/spl_crypto_service.cpp
index f358764b3..472036a3d 100644
--- a/stratosphere/spl/source/spl_crypto_service.cpp
+++ b/stratosphere/spl/source/spl_crypto_service.cpp
@@ -27,7 +27,7 @@ namespace ams::spl {
         return impl::GenerateAesKek(out_access_key.GetPointer(), key_source, generation, option);
     }
 
-    Result CryptoService::LoadAesKey(u32 keyslot, AccessKey access_key, KeySource key_source) {
+    Result CryptoService::LoadAesKey(s32 keyslot, AccessKey access_key, KeySource key_source) {
         return impl::LoadAesKey(keyslot, this, access_key, key_source);
     }
 
@@ -39,19 +39,19 @@ namespace ams::spl {
         return impl::DecryptAesKey(out_key.GetPointer(), key_source, generation, option);
     }
 
-    Result CryptoService::CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, u32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr) {
+    Result CryptoService::CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, s32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr) {
         return impl::CryptAesCtr(out_buf.GetPointer(), out_buf.GetSize(), keyslot, this, in_buf.GetPointer(), in_buf.GetSize(), iv_ctr);
     }
 
-    Result CryptoService::ComputeCmac(sf::Out<Cmac> out_cmac, u32 keyslot, const sf::InPointerBuffer &in_buf) {
+    Result CryptoService::ComputeCmac(sf::Out<Cmac> out_cmac, s32 keyslot, const sf::InPointerBuffer &in_buf) {
         return impl::ComputeCmac(out_cmac.GetPointer(), keyslot, this, in_buf.GetPointer(), in_buf.GetSize());
     }
 
-    Result CryptoService::AllocateAesKeyslot(sf::Out<u32> out_keyslot) {
+    Result CryptoService::AllocateAesKeyslot(sf::Out<s32> out_keyslot) {
         return impl::AllocateAesKeyslot(out_keyslot.GetPointer(), this);
     }
 
-    Result CryptoService::FreeAesKeyslot(u32 keyslot) {
+    Result CryptoService::FreeAesKeyslot(s32 keyslot) {
         return impl::FreeAesKeyslot(keyslot, this);
     }
 
diff --git a/stratosphere/spl/source/spl_crypto_service.hpp b/stratosphere/spl/source/spl_crypto_service.hpp
index 58841575c..8eec93dd8 100644
--- a/stratosphere/spl/source/spl_crypto_service.hpp
+++ b/stratosphere/spl/source/spl_crypto_service.hpp
@@ -25,13 +25,13 @@ namespace ams::spl {
         protected:
             /* Actual commands. */
             virtual Result GenerateAesKek(sf::Out<AccessKey> out_access_key, KeySource key_source, u32 generation, u32 option);
-            virtual Result LoadAesKey(u32 keyslot, AccessKey access_key, KeySource key_source);
+            virtual Result LoadAesKey(s32 keyslot, AccessKey access_key, KeySource key_source);
             virtual Result GenerateAesKey(sf::Out<AesKey> out_key, AccessKey access_key, KeySource key_source);
             virtual Result DecryptAesKey(sf::Out<AesKey> out_key, KeySource key_source, u32 generation, u32 option);
-            virtual Result CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, u32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr);
-            virtual Result ComputeCmac(sf::Out<Cmac> out_cmac, u32 keyslot, const sf::InPointerBuffer &in_buf);
-            virtual Result AllocateAesKeyslot(sf::Out<u32> out_keyslot);
-            virtual Result FreeAesKeyslot(u32 keyslot);
+            virtual Result CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, s32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr);
+            virtual Result ComputeCmac(sf::Out<Cmac> out_cmac, s32 keyslot, const sf::InPointerBuffer &in_buf);
+            virtual Result AllocateAesKeyslot(sf::Out<s32> out_keyslot);
+            virtual Result FreeAesKeyslot(s32 keyslot);
             virtual void GetAesKeyslotAvailableEvent(sf::OutCopyHandle out_hnd);
         public:
             DEFINE_SERVICE_DISPATCH_TABLE {
@@ -48,9 +48,9 @@ namespace ams::spl {
                 MAKE_SERVICE_COMMAND_META(DecryptAesKey),
                 MAKE_SERVICE_COMMAND_META(CryptAesCtr),
                 MAKE_SERVICE_COMMAND_META(ComputeCmac),
-                MAKE_SERVICE_COMMAND_META(AllocateAesKeyslot,          hos::Version_2_0_0),
-                MAKE_SERVICE_COMMAND_META(FreeAesKeyslot,              hos::Version_2_0_0),
-                MAKE_SERVICE_COMMAND_META(GetAesKeyslotAvailableEvent, hos::Version_2_0_0),
+                MAKE_SERVICE_COMMAND_META(AllocateAesKeyslot           /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
+                MAKE_SERVICE_COMMAND_META(FreeAesKeyslot               /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
+                MAKE_SERVICE_COMMAND_META(GetAesKeyslotAvailableEvent  /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
             };
     };
 
diff --git a/stratosphere/spl/source/spl_deprecated_service.cpp b/stratosphere/spl/source/spl_deprecated_service.cpp
index ead676cd4..a82c95955 100644
--- a/stratosphere/spl/source/spl_deprecated_service.cpp
+++ b/stratosphere/spl/source/spl_deprecated_service.cpp
@@ -30,7 +30,7 @@ namespace ams::spl {
         return impl::GenerateAesKek(out_access_key.GetPointer(), key_source, generation, option);
     }
 
-    Result DeprecatedService::LoadAesKey(u32 keyslot, AccessKey access_key, KeySource key_source) {
+    Result DeprecatedService::LoadAesKey(s32 keyslot, AccessKey access_key, KeySource key_source) {
         return impl::LoadAesKey(keyslot, this, access_key, key_source);
     }
 
@@ -70,15 +70,15 @@ namespace ams::spl {
         return impl::DecryptAesKey(out_key.GetPointer(), key_source, generation, option);
     }
 
-    Result DeprecatedService::CryptAesCtrDeprecated(const sf::OutBuffer &out_buf, u32 keyslot, const sf::InBuffer &in_buf, IvCtr iv_ctr) {
+    Result DeprecatedService::CryptAesCtrDeprecated(const sf::OutBuffer &out_buf, s32 keyslot, const sf::InBuffer &in_buf, IvCtr iv_ctr) {
         return impl::CryptAesCtr(out_buf.GetPointer(), out_buf.GetSize(), keyslot, this, in_buf.GetPointer(), in_buf.GetSize(), iv_ctr);
     }
 
-    Result DeprecatedService::CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, u32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr) {
+    Result DeprecatedService::CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, s32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr) {
         return impl::CryptAesCtr(out_buf.GetPointer(), out_buf.GetSize(), keyslot, this, in_buf.GetPointer(), in_buf.GetSize(), iv_ctr);
     }
 
-    Result DeprecatedService::ComputeCmac(sf::Out<Cmac> out_cmac, u32 keyslot, const sf::InPointerBuffer &in_buf) {
+    Result DeprecatedService::ComputeCmac(sf::Out<Cmac> out_cmac, s32 keyslot, const sf::InPointerBuffer &in_buf) {
         return impl::ComputeCmac(out_cmac.GetPointer(), keyslot, this, in_buf.GetPointer(), in_buf.GetSize());
     }
 
@@ -94,7 +94,7 @@ namespace ams::spl {
         return impl::UnwrapTitleKey(out_access_key.GetPointer(), base.GetPointer(), base.GetSize(), mod.GetPointer(), mod.GetSize(), label_digest.GetPointer(), label_digest.GetSize(), generation);
     }
 
-    Result DeprecatedService::LoadTitleKey(u32 keyslot, AccessKey access_key) {
+    Result DeprecatedService::LoadTitleKey(s32 keyslot, AccessKey access_key) {
         return impl::LoadTitleKey(keyslot, this, access_key);
     }
 
@@ -106,11 +106,11 @@ namespace ams::spl {
         return impl::UnwrapCommonTitleKey(out_access_key.GetPointer(), key_source, generation);
     }
 
-    Result DeprecatedService::AllocateAesKeyslot(sf::Out<u32> out_keyslot) {
+    Result DeprecatedService::AllocateAesKeyslot(sf::Out<s32> out_keyslot) {
         return impl::AllocateAesKeyslot(out_keyslot.GetPointer(), this);
     }
 
-    Result DeprecatedService::FreeAesKeyslot(u32 keyslot) {
+    Result DeprecatedService::FreeAesKeyslot(s32 keyslot) {
         return impl::FreeAesKeyslot(keyslot, this);
     }
 
diff --git a/stratosphere/spl/source/spl_deprecated_service.hpp b/stratosphere/spl/source/spl_deprecated_service.hpp
index 6274ed336..76c86138b 100644
--- a/stratosphere/spl/source/spl_deprecated_service.hpp
+++ b/stratosphere/spl/source/spl_deprecated_service.hpp
@@ -63,7 +63,7 @@ namespace ams::spl {
             virtual Result GetConfig(sf::Out<u64> out, u32 which);
             virtual Result ExpMod(const sf::OutPointerBuffer &out, const sf::InPointerBuffer &base, const sf::InPointerBuffer &exp, const sf::InPointerBuffer &mod);
             virtual Result GenerateAesKek(sf::Out<AccessKey> out_access_key, KeySource key_source, u32 generation, u32 option);
-            virtual Result LoadAesKey(u32 keyslot, AccessKey access_key, KeySource key_source);
+            virtual Result LoadAesKey(s32 keyslot, AccessKey access_key, KeySource key_source);
             virtual Result GenerateAesKey(sf::Out<AesKey> out_key, AccessKey access_key, KeySource key_source);
             virtual Result SetConfig(u32 which, u64 value);
             virtual Result GenerateRandomBytes(const sf::OutPointerBuffer &out);
@@ -73,17 +73,17 @@ namespace ams::spl {
             virtual Result GenerateSpecificAesKey(sf::Out<AesKey> out_key, KeySource key_source, u32 generation, u32 which);
             virtual Result DecryptRsaPrivateKey(const sf::OutPointerBuffer &dst, const sf::InPointerBuffer &src, AccessKey access_key, KeySource key_source, u32 option);
             virtual Result DecryptAesKey(sf::Out<AesKey> out_key, KeySource key_source, u32 generation, u32 option);
-            virtual Result CryptAesCtrDeprecated(const sf::OutBuffer &out_buf, u32 keyslot, const sf::InBuffer &in_buf, IvCtr iv_ctr);
-            virtual Result CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, u32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr);
-            virtual Result ComputeCmac(sf::Out<Cmac> out_cmac, u32 keyslot, const sf::InPointerBuffer &in_buf);
+            virtual Result CryptAesCtrDeprecated(const sf::OutBuffer &out_buf, s32 keyslot, const sf::InBuffer &in_buf, IvCtr iv_ctr);
+            virtual Result CryptAesCtr(const sf::OutNonSecureBuffer &out_buf, s32 keyslot, const sf::InNonSecureBuffer &in_buf, IvCtr iv_ctr);
+            virtual Result ComputeCmac(sf::Out<Cmac> out_cmac, s32 keyslot, const sf::InPointerBuffer &in_buf);
             virtual Result ImportEsKey(const sf::InPointerBuffer &src, AccessKey access_key, KeySource key_source, u32 option);
             virtual Result UnwrapTitleKeyDeprecated(sf::Out<AccessKey> out_access_key, const sf::InPointerBuffer &base, const sf::InPointerBuffer &mod, const sf::InPointerBuffer &label_digest);
             virtual Result UnwrapTitleKey(sf::Out<AccessKey> out_access_key, const sf::InPointerBuffer &base, const sf::InPointerBuffer &mod, const sf::InPointerBuffer &label_digest, u32 generation);
-            virtual Result LoadTitleKey(u32 keyslot, AccessKey access_key);
+            virtual Result LoadTitleKey(s32 keyslot, AccessKey access_key);
             virtual Result UnwrapCommonTitleKeyDeprecated(sf::Out<AccessKey> out_access_key, KeySource key_source);
             virtual Result UnwrapCommonTitleKey(sf::Out<AccessKey> out_access_key, KeySource key_source, u32 generation);
-            virtual Result AllocateAesKeyslot(sf::Out<u32> out_keyslot);
-            virtual Result FreeAesKeyslot(u32 keyslot);
+            virtual Result AllocateAesKeyslot(sf::Out<s32> out_keyslot);
+            virtual Result FreeAesKeyslot(s32 keyslot);
             virtual void GetAesKeyslotAvailableEvent(sf::OutCopyHandle out_hnd);
             virtual Result SetBootReason(BootReasonValue boot_reason);
             virtual Result GetBootReason(sf::Out<BootReasonValue> out);
@@ -117,9 +117,9 @@ namespace ams::spl {
                 MAKE_SERVICE_COMMAND_META(UnwrapCommonTitleKeyDeprecated, hos::Version_2_0_0, hos::Version_2_0_0),
                 MAKE_SERVICE_COMMAND_META(UnwrapCommonTitleKey,           hos::Version_3_0_0),
 
-                MAKE_SERVICE_COMMAND_META(AllocateAesKeyslot,             hos::Version_2_0_0),
-                MAKE_SERVICE_COMMAND_META(FreeAesKeyslot,                 hos::Version_2_0_0),
-                MAKE_SERVICE_COMMAND_META(GetAesKeyslotAvailableEvent,    hos::Version_2_0_0),
+                MAKE_SERVICE_COMMAND_META(AllocateAesKeyslot              /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
+                MAKE_SERVICE_COMMAND_META(FreeAesKeyslot                  /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
+                MAKE_SERVICE_COMMAND_META(GetAesKeyslotAvailableEvent     /* Atmosphere extension: This was added in hos::Version_2_0_0, but is allowed on older firmware by atmosphere. */),
 
                 MAKE_SERVICE_COMMAND_META(SetBootReason,                  hos::Version_3_0_0),
                 MAKE_SERVICE_COMMAND_META(GetBootReason,                  hos::Version_3_0_0),
diff --git a/stratosphere/spl/source/spl_es_service.cpp b/stratosphere/spl/source/spl_es_service.cpp
index 723e1db9c..d1e21179e 100644
--- a/stratosphere/spl/source/spl_es_service.cpp
+++ b/stratosphere/spl/source/spl_es_service.cpp
@@ -46,7 +46,7 @@ namespace ams::spl {
         return impl::UnwrapElicenseKey(out_access_key.GetPointer(), base.GetPointer(), base.GetSize(), mod.GetPointer(), mod.GetSize(), label_digest.GetPointer(), label_digest.GetSize(), generation);
     }
 
-    Result EsService::LoadElicenseKey(u32 keyslot, AccessKey access_key) {
+    Result EsService::LoadElicenseKey(s32 keyslot, AccessKey access_key) {
         return impl::LoadElicenseKey(keyslot, this, access_key);
     }
 
diff --git a/stratosphere/spl/source/spl_es_service.hpp b/stratosphere/spl/source/spl_es_service.hpp
index 82989d4ba..829cc4a86 100644
--- a/stratosphere/spl/source/spl_es_service.hpp
+++ b/stratosphere/spl/source/spl_es_service.hpp
@@ -31,7 +31,7 @@ namespace ams::spl {
             virtual Result ImportDrmKey(const sf::InPointerBuffer &src, AccessKey access_key, KeySource key_source);
             virtual Result DrmExpMod(const sf::OutPointerBuffer &out, const sf::InPointerBuffer &base, const sf::InPointerBuffer &mod);
             virtual Result UnwrapElicenseKey(sf::Out<AccessKey> out_access_key, const sf::InPointerBuffer &base, const sf::InPointerBuffer &mod, const sf::InPointerBuffer &label_digest, u32 generation);
-            virtual Result LoadElicenseKey(u32 keyslot, AccessKey access_key);
+            virtual Result LoadElicenseKey(s32 keyslot, AccessKey access_key);
         public:
             DEFINE_SERVICE_DISPATCH_TABLE {
                 MAKE_SERVICE_COMMAND_META(GetConfig),
diff --git a/stratosphere/spl/source/spl_fs_service.cpp b/stratosphere/spl/source/spl_fs_service.cpp
index 8e201b9ae..f74ec8e7a 100644
--- a/stratosphere/spl/source/spl_fs_service.cpp
+++ b/stratosphere/spl/source/spl_fs_service.cpp
@@ -34,7 +34,7 @@ namespace ams::spl {
         return impl::GenerateSpecificAesKey(out_key.GetPointer(), key_source, generation, which);
     }
 
-    Result FsService::LoadTitleKey(u32 keyslot, AccessKey access_key) {
+    Result FsService::LoadTitleKey(s32 keyslot, AccessKey access_key) {
         return impl::LoadTitleKey(keyslot, this, access_key);
     }
 
diff --git a/stratosphere/spl/source/spl_fs_service.hpp b/stratosphere/spl/source/spl_fs_service.hpp
index 7b13303ee..b9a48781f 100644
--- a/stratosphere/spl/source/spl_fs_service.hpp
+++ b/stratosphere/spl/source/spl_fs_service.hpp
@@ -28,7 +28,7 @@ namespace ams::spl {
             virtual Result ImportLotusKey(const sf::InPointerBuffer &src, AccessKey access_key, KeySource key_source);
             virtual Result DecryptLotusMessage(sf::Out<u32> out_size, const sf::OutPointerBuffer &out, const sf::InPointerBuffer &base, const sf::InPointerBuffer &mod, const sf::InPointerBuffer &label_digest);
             virtual Result GenerateSpecificAesKey(sf::Out<AesKey> out_key, KeySource key_source, u32 generation, u32 which);
-            virtual Result LoadTitleKey(u32 keyslot, AccessKey access_key);
+            virtual Result LoadTitleKey(s32 keyslot, AccessKey access_key);
             virtual Result GetPackage2Hash(const sf::OutPointerBuffer &dst);
         public:
             DEFINE_SERVICE_DISPATCH_TABLE {
diff --git a/stratosphere/spl/source/spl_key_slot_cache.hpp b/stratosphere/spl/source/spl_key_slot_cache.hpp
new file mode 100644
index 000000000..18c093dc8
--- /dev/null
+++ b/stratosphere/spl/source/spl_key_slot_cache.hpp
@@ -0,0 +1,138 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::spl {
+
+    class KeySlotCacheEntry : public util::IntrusiveListBaseNode<KeySlotCacheEntry> {
+        NON_COPYABLE(KeySlotCacheEntry);
+        NON_MOVEABLE(KeySlotCacheEntry);
+        private:
+            friend class KeySlotCache;
+        public:
+            static constexpr size_t KeySize = crypto::AesDecryptor128::KeySize;
+        private:
+            const s32 slot_index;
+            s32 virtual_slot;
+        public:
+            explicit KeySlotCacheEntry(s32 idx) : slot_index(idx), virtual_slot(-1) { /* ... */ }
+
+            bool Contains(s32 virtual_slot) const {
+                return virtual_slot == this->virtual_slot;
+            }
+
+            s32 GetPhysicalKeySlotIndex() const { return this->slot_index; }
+
+            s32 GetVirtualKeySlotIndex() const { return this->virtual_slot; }
+
+            void SetVirtualSlot(s32 virtual_slot) {
+                this->virtual_slot = virtual_slot;
+            }
+
+            void ClearVirtualSlot() {
+                this->virtual_slot = -1;
+            }
+    };
+
+    class KeySlotCache {
+        NON_COPYABLE(KeySlotCache);
+        NON_MOVEABLE(KeySlotCache);
+        private:
+            using KeySlotCacheEntryList = util::IntrusiveListBaseTraits<KeySlotCacheEntry>::ListType;
+        private:
+            KeySlotCacheEntryList mru_list;
+        public:
+            constexpr KeySlotCache() : mru_list() { /* ... */ }
+
+            s32 Allocate(s32 virtual_slot) {
+                return this->AllocateFromLru(virtual_slot);
+            }
+
+            bool Find(s32 *out, s32 virtual_slot) {
+                for (auto it = this->mru_list.begin(); it != this->mru_list.end(); ++it) {
+                    if (it->Contains(virtual_slot)) {
+                        *out = it->GetPhysicalKeySlotIndex();
+
+                        this->UpdateMru(it);
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+
+            bool Release(s32 *out, s32 virtual_slot) {
+                for (auto it = this->mru_list.begin(); it != this->mru_list.end(); ++it) {
+                    if (it->Contains(virtual_slot)) {
+                        *out = it->GetPhysicalKeySlotIndex();
+                        it->ClearVirtualSlot();
+
+                        this->UpdateLru(it);
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+
+            bool FindPhysical(s32 physical_slot) {
+                for (auto it = this->mru_list.begin(); it != this->mru_list.end(); ++it) {
+                    if (it->GetPhysicalKeySlotIndex() == physical_slot) {
+                        this->UpdateMru(it);
+
+                        if (it->GetVirtualKeySlotIndex() == physical_slot) {
+                            return true;
+                        } else {
+                            it->SetVirtualSlot(physical_slot);
+                            return false;
+                        }
+                    }
+                }
+                AMS_ABORT();
+            }
+
+            void AddEntry(KeySlotCacheEntry *entry) {
+                this->mru_list.push_front(*entry);
+            }
+        private:
+            s32 AllocateFromLru(s32 virtual_slot) {
+                AMS_ASSERT(!this->mru_list.empty());
+
+                auto it = this->mru_list.rbegin();
+                it->SetVirtualSlot(virtual_slot);
+
+                auto *entry = std::addressof(*it);
+                this->mru_list.pop_back();
+                this->mru_list.push_front(*entry);
+
+                return entry->GetPhysicalKeySlotIndex();
+            }
+
+            void UpdateMru(KeySlotCacheEntryList::iterator it) {
+                auto *entry = std::addressof(*it);
+                this->mru_list.erase(it);
+                this->mru_list.push_front(*entry);
+            }
+
+            void UpdateLru(KeySlotCacheEntryList::iterator it) {
+                auto *entry = std::addressof(*it);
+                this->mru_list.erase(it);
+                this->mru_list.push_back(*entry);
+            }
+    };
+
+}