diff --git a/KeyStorage.cpp b/KeyStorage.cpp
new file mode 100644
index 0000000..d435539
--- /dev/null
+++ b/KeyStorage.cpp
@@ -0,0 +1,254 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "KeyStorage.h"
+
+#include "Keymaster.h"
+#include "Utils.h"
+
+#include <vector>
+
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <openssl/sha.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+
+#include <keymaster/authorization_set.h>
+
+namespace android {
+namespace vold {
+
+static constexpr size_t AES_KEY_BYTES = 32;
+static constexpr size_t GCM_NONCE_BYTES = 12;
+static constexpr size_t GCM_MAC_BYTES = 16;
+// FIXME: better name than "secdiscardable" sought!
+static constexpr size_t SECDISCARDABLE_BYTES = 1<<14;
+
+static const char* kRmPath = "/system/bin/rm";
+static const char* kSecdiscardPath = "/system/bin/secdiscard";
+static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
+static const char* kFn_encrypted_key = "encrypted_key";
+static const char* kFn_secdiscardable = "secdiscardable";
+
+static bool CheckSize(const std::string& kind, size_t actual, size_t expected) {
+    if (actual != expected) {
+        LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected
+            << " got " << actual;
+        return false;
+    }
+    return true;
+}
+
+static std::string HashSecdiscardable(const std::string &secdiscardable) {
+    SHA512_CTX c;
+
+    SHA512_Init(&c);
+    // Personalise the hashing by introducing a fixed prefix.
+    // Hashing applications should use personalization except when there is a
+    // specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
+    std::string secdiscardable_hashing_prefix = "Android secdiscardable SHA512";
+    secdiscardable_hashing_prefix.resize(SHA512_CBLOCK);
+    SHA512_Update(&c, secdiscardable_hashing_prefix.data(), secdiscardable_hashing_prefix.size());
+    SHA512_Update(&c, secdiscardable.data(), secdiscardable.size());
+    std::string res(SHA512_DIGEST_LENGTH, '\0');
+    SHA512_Final(reinterpret_cast<uint8_t *>(&res[0]), &c);
+    return res;
+}
+
+static bool GenerateKeymasterKey(Keymaster &keymaster,
+        const keymaster::AuthorizationSet &extra_params,
+        std::string &key) {
+    keymaster::AuthorizationSetBuilder param_builder;
+    param_builder
+        .AesEncryptionKey(AES_KEY_BYTES * 8)
+        .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
+        .Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
+        .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
+        .Authorization(keymaster::TAG_NO_AUTH_REQUIRED); // FIXME integrate with gatekeeper
+    auto params = param_builder.build();
+    params.push_back(extra_params);
+    return keymaster.GenerateKey(params, key);
+}
+
+static bool EncryptWithKeymasterKey(
+        Keymaster &keymaster,
+        const std::string &key,
+        const keymaster::AuthorizationSet &extra_params,
+        const std::string &message,
+        std::string &ciphertext) {
+    // FIXME fix repetition
+    keymaster::AuthorizationSetBuilder param_builder;
+    param_builder
+        .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
+        .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
+        .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
+    auto params = param_builder.build();
+    params.push_back(extra_params);
+    keymaster::AuthorizationSet out_params;
+    auto op_handle = keymaster.Begin(KM_PURPOSE_ENCRYPT, key, params, out_params);
+    if (!op_handle) return false;
+    keymaster_blob_t nonce_blob;
+    if (!out_params.GetTagValue(keymaster::TAG_NONCE, &nonce_blob)) {
+        LOG(ERROR) << "GCM encryption but no nonce generated";
+        return false;
+    }
+    // nonce_blob here is just a pointer into existing data, must not be freed
+    std::string nonce(reinterpret_cast<const char *>(nonce_blob.data), nonce_blob.data_length);
+    if (!CheckSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
+    std::string body;
+    if (!op_handle.UpdateCompletely(message, body)) return false;
+
+    std::string mac;
+    if (!op_handle.FinishWithOutput(mac)) return false;
+    if (!CheckSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
+    ciphertext = nonce + body + mac;
+    return true;
+}
+
+static bool DecryptWithKeymasterKey(
+        Keymaster &keymaster, const std::string &key,
+        const keymaster::AuthorizationSet &extra_params,
+        const std::string &ciphertext,
+        std::string &message) {
+    auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
+    auto body_mac = ciphertext.substr(GCM_NONCE_BYTES);
+    // FIXME fix repetition
+    keymaster::AuthorizationSetBuilder param_builder;
+    param_builder
+        .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
+        .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
+        .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
+    AddStringParam(param_builder, keymaster::TAG_NONCE, nonce);
+    auto params = param_builder.build();
+    params.push_back(extra_params);
+
+    auto op_handle = keymaster.Begin(KM_PURPOSE_DECRYPT, key, params);
+    if (!op_handle) return false;
+    if (!op_handle.UpdateCompletely(body_mac, message)) return false;
+    if (!op_handle.Finish()) return false;
+    return true;
+}
+
+bool StoreKey(const std::string &dir, const std::string &key) {
+    if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
+        PLOG(ERROR) << "key mkdir " << dir;
+        return false;
+    }
+    std::string secdiscardable;
+    if (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != 0) {
+        // TODO status_t plays badly with PLOG, fix it.
+        LOG(ERROR) << "Random read failed";
+        return false;
+    }
+    // FIXME create a wrapper around reads and writes which handles error logging
+    if (!android::base::WriteStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) {
+         PLOG(ERROR) << "Unable to write secdiscardable to " << dir;
+         return false;
+    }
+    keymaster::AuthorizationSetBuilder param_builder;
+    AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
+        HashSecdiscardable(secdiscardable));
+    auto extra_params = param_builder.build();
+    Keymaster keymaster;
+    if (!keymaster) return false;
+    std::string km_key;
+    if (!GenerateKeymasterKey(keymaster, extra_params, km_key)) return false;
+    std::string encrypted_key;
+    if (!EncryptWithKeymasterKey(
+        keymaster, km_key, extra_params, key, encrypted_key)) return false;
+    if (!android::base::WriteStringToFile(km_key, dir + "/" + kFn_keymaster_key_blob)) {
+        PLOG(ERROR) << "Unable to write keymaster_key_blob to " << dir;
+        return false;
+    }
+    if (!android::base::WriteStringToFile(encrypted_key, dir + "/" + kFn_encrypted_key)) {
+        PLOG(ERROR) << "Unable to write encrypted_key to " << dir;
+        return false;
+    }
+    return true;
+}
+
+bool RetrieveKey(const std::string &dir, std::string &key) {
+    std::string secdiscardable;
+    if (!android::base::ReadFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) {
+         PLOG(ERROR) << "Unable to read secdiscardable from " << dir;
+         return false;
+    }
+    keymaster::AuthorizationSetBuilder param_builder;
+    AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
+        HashSecdiscardable(secdiscardable));
+    auto extra_params = param_builder.build();
+    std::string km_key;
+    if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
+         PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
+         return false;
+    }
+    std::string encrypted_message;
+    if (!android::base::ReadFileToString(dir + "/" + kFn_encrypted_key, &encrypted_message)) {
+         PLOG(ERROR) << "Unable to read encrypted_key to " << dir;
+         return false;
+    }
+    Keymaster keymaster;
+    if (!keymaster) return false;
+    return DecryptWithKeymasterKey(keymaster, km_key, extra_params, encrypted_message, key);
+}
+
+static bool DeleteKey(const std::string &dir) {
+    std::string km_key;
+    if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
+         PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
+         return false;
+    }
+    Keymaster keymaster;
+    if (!keymaster) return false;
+    if (!keymaster.DeleteKey(km_key)) return false;
+    return true;
+}
+
+static bool SecdiscardSecdiscardable(const std::string &dir) {
+    if (ForkExecvp(std::vector<std::string> {
+            kSecdiscardPath, "--", dir + "/" + kFn_secdiscardable}) != 0) {
+        LOG(ERROR) << "secdiscard failed";
+        return false;
+    }
+    return true;
+}
+
+static bool RecursiveDeleteKey(const std::string &dir) {
+    if (ForkExecvp(std::vector<std::string> {
+            kRmPath, "-rf", dir}) != 0) {
+        LOG(ERROR) << "recursive delete failed";
+        return false;
+    }
+    return true;
+}
+
+bool DestroyKey(const std::string &dir) {
+    bool success = true;
+    // Try each thing, even if previous things failed.
+    success &= DeleteKey(dir);
+    success &= SecdiscardSecdiscardable(dir);
+    success &= RecursiveDeleteKey(dir);
+    return success;
+}
+
+}  // namespace vold
+}  // namespace android