Support keys with a secret but no token, which are handled not using
Keymaster but in-process crypto.
Bug: 33384925
Test: manual for now: patch KeyAuthentication.usesKeymaster() to always return true;
flash a FBE device, add a device PIN, reboot and verify PIN can unlock FBE.
Then clear device PIN, reboot and verify FBE is unlocked automatically.
In both cases, check there is no keymaster_key_blob in
/data/misc/vold/user_keys/ce/0/current/
Unit tests to be added.
Change-Id: Ia94e2b39d60bfd98c7a8347a5ba043eeab6928c5
diff --git a/KeyStorage.cpp b/KeyStorage.cpp
index 9cb8ca0..9a1304c 100644
--- a/KeyStorage.cpp
+++ b/KeyStorage.cpp
@@ -29,6 +29,8 @@
#include <sys/wait.h>
#include <unistd.h>
+#include <openssl/err.h>
+#include <openssl/evp.h>
#include <openssl/sha.h>
#include <android-base/file.h>
@@ -67,6 +69,8 @@
static const char* kStretch_none = "none";
static const char* kStretch_nopassword = "nopassword";
static const std::string kStretchPrefix_scrypt = "scrypt ";
+static const char* kHashPrefix_secdiscardable = "Android secdiscardable SHA512";
+static const char* kHashPrefix_keygen = "Android key wrapping key generation SHA512";
static const char* kFn_encrypted_key = "encrypted_key";
static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
static const char* kFn_keymaster_key_blob_upgraded = "keymaster_key_blob_upgraded";
@@ -84,17 +88,17 @@
return true;
}
-static std::string hashSecdiscardable(const std::string& secdiscardable) {
+static std::string hashWithPrefix(char const* prefix, const std::string& tohash) {
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 secdiscardableHashingPrefix = "Android secdiscardable SHA512";
- secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
- SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
- SHA512_Update(&c, secdiscardable.data(), secdiscardable.size());
+ std::string hashingPrefix = prefix;
+ hashingPrefix.resize(SHA512_CBLOCK);
+ SHA512_Update(&c, hashingPrefix.data(), hashingPrefix.size());
+ SHA512_Update(&c, tohash.data(), tohash.size());
std::string res(SHA512_DIGEST_LENGTH, '\0');
SHA512_Final(reinterpret_cast<uint8_t*>(&res[0]), &c);
return res;
@@ -228,11 +232,17 @@
return true;
}
-static std::string getStretching() {
- char paramstr[PROPERTY_VALUE_MAX];
+static std::string getStretching(const KeyAuthentication& auth) {
+ if (!auth.usesKeymaster()) {
+ return kStretch_none;
+ } else if (auth.secret.empty()) {
+ return kStretch_nopassword;
+ } else {
+ char paramstr[PROPERTY_VALUE_MAX];
- property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
- return std::string() + kStretchPrefix_scrypt + paramstr;
+ property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
+ return std::string() + kStretchPrefix_scrypt + paramstr;
+ }
}
static bool stretchingNeedsSalt(const std::string& stretching) {
@@ -277,7 +287,116 @@
std::string* appId) {
std::string stretched;
if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
- *appId = hashSecdiscardable(secdiscardable) + stretched;
+ *appId = hashWithPrefix(kHashPrefix_secdiscardable, secdiscardable) + stretched;
+ return true;
+}
+
+static bool readRandomBytesOrLog(size_t count, std::string* out) {
+ auto status = ReadRandomBytes(count, *out);
+ if (status != OK) {
+ LOG(ERROR) << "Random read failed with status: " << status;
+ return false;
+ }
+ return true;
+}
+
+static void logOpensslError() {
+ LOG(ERROR) << "Openssl error: " << ERR_get_error();
+}
+
+static bool encryptWithoutKeymaster(const std::string& preKey,
+ const std::string& plaintext, std::string* ciphertext) {
+ auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
+ key.resize(AES_KEY_BYTES);
+ if (!readRandomBytesOrLog(GCM_NONCE_BYTES, ciphertext)) return false;
+ auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
+ EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
+ if (!ctx) {
+ logOpensslError();
+ return false;
+ }
+ if (1 != EVP_EncryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
+ reinterpret_cast<const uint8_t*>(key.data()),
+ reinterpret_cast<const uint8_t*>(ciphertext->data()))) {
+ logOpensslError();
+ return false;
+ }
+ ciphertext->resize(GCM_NONCE_BYTES + plaintext.size() + GCM_MAC_BYTES);
+ int outlen;
+ if (1 != EVP_EncryptUpdate(ctx.get(),
+ reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES), &outlen,
+ reinterpret_cast<const uint8_t*>(plaintext.data()), plaintext.size())) {
+ logOpensslError();
+ return false;
+ }
+ if (outlen != static_cast<int>(plaintext.size())) {
+ LOG(ERROR) << "GCM ciphertext length should be " << plaintext.size() << " was " << outlen;
+ return false;
+ }
+ if (1 != EVP_EncryptFinal_ex(ctx.get(),
+ reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()), &outlen)) {
+ logOpensslError();
+ return false;
+ }
+ if (outlen != 0) {
+ LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
+ return false;
+ }
+ if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_GET_TAG, GCM_MAC_BYTES,
+ reinterpret_cast<uint8_t*>(&(*ciphertext)[0] + GCM_NONCE_BYTES + plaintext.size()))) {
+ logOpensslError();
+ return false;
+ }
+ return true;
+}
+
+static bool decryptWithoutKeymaster(const std::string& preKey,
+ const std::string& ciphertext, std::string* plaintext) {
+ if (ciphertext.size() < GCM_NONCE_BYTES + GCM_MAC_BYTES) {
+ LOG(ERROR) << "GCM ciphertext too small: " << ciphertext.size();
+ return false;
+ }
+ auto key = hashWithPrefix(kHashPrefix_keygen, preKey);
+ key.resize(AES_KEY_BYTES);
+ auto ctx = std::unique_ptr<EVP_CIPHER_CTX, decltype(&::EVP_CIPHER_CTX_free)>(
+ EVP_CIPHER_CTX_new(), EVP_CIPHER_CTX_free);
+ if (!ctx) {
+ logOpensslError();
+ return false;
+ }
+ if (1 != EVP_DecryptInit_ex(ctx.get(), EVP_aes_256_gcm(), NULL,
+ reinterpret_cast<const uint8_t*>(key.data()),
+ reinterpret_cast<const uint8_t*>(ciphertext.data()))) {
+ logOpensslError();
+ return false;
+ }
+ plaintext->resize(ciphertext.size() - GCM_NONCE_BYTES - GCM_MAC_BYTES);
+ int outlen;
+ if (1 != EVP_DecryptUpdate(ctx.get(),
+ reinterpret_cast<uint8_t*>(&(*plaintext)[0]), &outlen,
+ reinterpret_cast<const uint8_t*>(ciphertext.data() + GCM_NONCE_BYTES), plaintext->size())) {
+ logOpensslError();
+ return false;
+ }
+ if (outlen != static_cast<int>(plaintext->size())) {
+ LOG(ERROR) << "GCM plaintext length should be " << plaintext->size() << " was " << outlen;
+ return false;
+ }
+ if (1 != EVP_CIPHER_CTX_ctrl(ctx.get(), EVP_CTRL_GCM_SET_TAG, GCM_MAC_BYTES,
+ const_cast<void *>(
+ reinterpret_cast<const void*>(ciphertext.data() + GCM_NONCE_BYTES + plaintext->size())))) {
+ logOpensslError();
+ return false;
+ }
+ if (1 != EVP_DecryptFinal_ex(ctx.get(),
+ reinterpret_cast<uint8_t*>(&(*plaintext)[0] + plaintext->size()), &outlen)) {
+ logOpensslError();
+ return false;
+ }
+ if (outlen != 0) {
+ LOG(ERROR) << "GCM EncryptFinal should be 0, was " << outlen;
+ return false;
+ }
return true;
}
@@ -288,13 +407,9 @@
}
if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) return false;
std::string secdiscardable;
- if (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
- // TODO status_t plays badly with PLOG, fix it.
- LOG(ERROR) << "Random read failed";
- return false;
- }
+ if (!readRandomBytesOrLog(SECDISCARDABLE_BYTES, &secdiscardable)) return false;
if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
- std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
+ std::string stretching = getStretching(auth);
if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
@@ -306,14 +421,18 @@
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
- Keymaster keymaster;
- if (!keymaster) return false;
- std::string kmKey;
- if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
- if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
- auto keyParams = beginParams(auth, appId);
std::string encryptedKey;
- if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
+ if (auth.usesKeymaster()) {
+ Keymaster keymaster;
+ if (!keymaster) return false;
+ std::string kmKey;
+ if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
+ if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
+ auto keyParams = beginParams(auth, appId);
+ if (!encryptWithKeymasterKey(keymaster, dir, keyParams, key, &encryptedKey)) return false;
+ } else {
+ if (!encryptWithoutKeymaster(appId, key, &encryptedKey)) return false;
+ }
if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
return true;
}
@@ -337,10 +456,15 @@
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
std::string encryptedMessage;
if (!readFileToString(dir + "/" + kFn_encrypted_key, &encryptedMessage)) return false;
- Keymaster keymaster;
- if (!keymaster) return false;
- auto keyParams = beginParams(auth, appId);
- return decryptWithKeymasterKey(keymaster, dir, keyParams, encryptedMessage, key);
+ if (auth.usesKeymaster()) {
+ Keymaster keymaster;
+ if (!keymaster) return false;
+ auto keyParams = beginParams(auth, appId);
+ if (!decryptWithKeymasterKey(keymaster, dir, keyParams, encryptedMessage, key)) return false;
+ } else {
+ if (!decryptWithoutKeymaster(appId, encryptedMessage, key)) return false;
+ }
+ return true;
}
static bool deleteKey(const std::string& dir) {