keystore2/src/super_key.rs

// Copyright 2020, 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.

use crate::{
    boot_level_keys::{get_level_zero_key, BootLevelKeyCache},
    database::BlobMetaData,
    database::BlobMetaEntry,
    database::EncryptedBy,
    database::KeyEntry,
    database::KeyType,
    database::{KeyEntryLoadBits, KeyIdGuard, KeyMetaData, KeyMetaEntry, KeystoreDB},
    ec_crypto::ECDHPrivateKey,
    enforcements::Enforcements,
    error::Error,
    error::ResponseCode,
    key_parameter::{KeyParameter, KeyParameterValue},
    ks_err,
    legacy_importer::LegacyImporter,
    raw_device::KeyMintDevice,
    utils::{watchdog as wd, AesGcm, AID_KEYSTORE},
};
use android_hardware_security_keymint::aidl::android::hardware::security::keymint::{
    Algorithm::Algorithm, BlockMode::BlockMode, HardwareAuthToken::HardwareAuthToken,
    HardwareAuthenticatorType::HardwareAuthenticatorType, KeyFormat::KeyFormat,
    KeyParameter::KeyParameter as KmKeyParameter, KeyPurpose::KeyPurpose, PaddingMode::PaddingMode,
    SecurityLevel::SecurityLevel,
};
use android_system_keystore2::aidl::android::system::keystore2::{
    Domain::Domain, KeyDescriptor::KeyDescriptor,
};
use anyhow::{Context, Result};
use keystore2_crypto::{
    aes_gcm_decrypt, aes_gcm_encrypt, generate_aes256_key, generate_salt, Password, ZVec,
    AES_256_KEY_LENGTH,
};
use rustutils::system_properties::PropertyWatcher;
use std::{
    collections::HashMap,
    sync::Arc,
    sync::{Mutex, RwLock, Weak},
};
use std::{convert::TryFrom, ops::Deref};

const MAX_MAX_BOOT_LEVEL: usize = 1_000_000_000;
/// Allow up to 15 seconds between the user unlocking using a biometric, and the auth
/// token being used to unlock in [`SuperKeyManager::try_unlock_user_with_biometric`].
/// This seems short enough for security purposes, while long enough that even the
/// very slowest device will present the auth token in time.
const BIOMETRIC_AUTH_TIMEOUT_S: i32 = 15; // seconds

type UserId = u32;

/// Encryption algorithm used by a particular type of superencryption key
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SuperEncryptionAlgorithm {
    /// Symmetric encryption with AES-256-GCM
    Aes256Gcm,
    /// Public-key encryption with ECDH P-521
    EcdhP521,
}

/// A particular user may have several superencryption keys in the database, each for a
/// different purpose, distinguished by alias. Each is associated with a static
/// constant of this type.
pub struct SuperKeyType<'a> {
    /// Alias used to look up the key in the `persistent.keyentry` table.
    pub alias: &'a str,
    /// Encryption algorithm
    pub algorithm: SuperEncryptionAlgorithm,
}

/// Key used for LskfLocked keys; the corresponding superencryption key is loaded in memory
/// when the user first unlocks, and remains in memory until the device reboots.
pub const USER_SUPER_KEY: SuperKeyType =
    SuperKeyType { alias: "USER_SUPER_KEY", algorithm: SuperEncryptionAlgorithm::Aes256Gcm };
/// Key used for ScreenLockBound keys; the corresponding superencryption key is loaded in memory
/// each time the user enters their LSKF, and cleared from memory each time the device is locked.
/// Symmetric.
pub const USER_SCREEN_LOCK_BOUND_KEY: SuperKeyType = SuperKeyType {
    alias: "USER_SCREEN_LOCK_BOUND_KEY",
    algorithm: SuperEncryptionAlgorithm::Aes256Gcm,
};
/// Key used for ScreenLockBound keys; the corresponding superencryption key is loaded in memory
/// each time the user enters their LSKF, and cleared from memory each time the device is locked.
/// Asymmetric, so keys can be encrypted when the device is locked.
pub const USER_SCREEN_LOCK_BOUND_P521_KEY: SuperKeyType = SuperKeyType {
    alias: "USER_SCREEN_LOCK_BOUND_P521_KEY",
    algorithm: SuperEncryptionAlgorithm::EcdhP521,
};

/// Superencryption to apply to a new key.
#[derive(Debug, Clone, Copy)]
pub enum SuperEncryptionType {
    /// Do not superencrypt this key.
    None,
    /// Superencrypt with a key that remains in memory from first unlock to reboot.
    LskfBound,
    /// Superencrypt with a key cleared from memory when the device is locked.
    ScreenLockBound,
    /// Superencrypt with a key based on the desired boot level
    BootLevel(i32),
}

#[derive(Debug, Clone, Copy)]
pub enum SuperKeyIdentifier {
    /// id of the super key in the database.
    DatabaseId(i64),
    /// Boot level of the encrypting boot level key
    BootLevel(i32),
}

impl SuperKeyIdentifier {
    fn from_metadata(metadata: &BlobMetaData) -> Option<Self> {
        if let Some(EncryptedBy::KeyId(key_id)) = metadata.encrypted_by() {
            Some(SuperKeyIdentifier::DatabaseId(*key_id))
        } else {
            metadata.max_boot_level().map(|boot_level| SuperKeyIdentifier::BootLevel(*boot_level))
        }
    }

    fn add_to_metadata(&self, metadata: &mut BlobMetaData) {
        match self {
            SuperKeyIdentifier::DatabaseId(id) => {
                metadata.add(BlobMetaEntry::EncryptedBy(EncryptedBy::KeyId(*id)));
            }
            SuperKeyIdentifier::BootLevel(level) => {
                metadata.add(BlobMetaEntry::MaxBootLevel(*level));
            }
        }
    }
}

pub struct SuperKey {
    algorithm: SuperEncryptionAlgorithm,
    key: ZVec,
    /// Identifier of the encrypting key, used to write an encrypted blob
    /// back to the database after re-encryption eg on a key update.
    id: SuperKeyIdentifier,
    /// ECDH is more expensive than AES. So on ECDH private keys we set the
    /// reencrypt_with field to point at the corresponding AES key, and the
    /// keys will be re-encrypted with AES on first use.
    reencrypt_with: Option<Arc<SuperKey>>,
}

impl AesGcm for SuperKey {
    fn decrypt(&self, data: &[u8], iv: &[u8], tag: &[u8]) -> Result<ZVec> {
        if self.algorithm == SuperEncryptionAlgorithm::Aes256Gcm {
            aes_gcm_decrypt(data, iv, tag, &self.key).context(ks_err!("Decryption failed."))
        } else {
            Err(Error::sys()).context(ks_err!("Key is not an AES key."))
        }
    }

    fn encrypt(&self, plaintext: &[u8]) -> Result<(Vec<u8>, Vec<u8>, Vec<u8>)> {
        if self.algorithm == SuperEncryptionAlgorithm::Aes256Gcm {
            aes_gcm_encrypt(plaintext, &self.key).context(ks_err!("Encryption failed."))
        } else {
            Err(Error::sys()).context(ks_err!("Key is not an AES key."))
        }
    }
}

/// A SuperKey that has been encrypted with an AES-GCM key. For
/// encryption the key is in memory, and for decryption it is in KM.
struct LockedKey {
    algorithm: SuperEncryptionAlgorithm,
    id: SuperKeyIdentifier,
    nonce: Vec<u8>,
    ciphertext: Vec<u8>, // with tag appended
}

impl LockedKey {
    fn new(key: &[u8], to_encrypt: &Arc<SuperKey>) -> Result<Self> {
        let (mut ciphertext, nonce, mut tag) = aes_gcm_encrypt(&to_encrypt.key, key)?;
        ciphertext.append(&mut tag);
        Ok(LockedKey { algorithm: to_encrypt.algorithm, id: to_encrypt.id, nonce, ciphertext })
    }

    fn decrypt(
        &self,
        db: &mut KeystoreDB,
        km_dev: &KeyMintDevice,
        key_id_guard: &KeyIdGuard,
        key_entry: &KeyEntry,
        auth_token: &HardwareAuthToken,
        reencrypt_with: Option<Arc<SuperKey>>,
    ) -> Result<Arc<SuperKey>> {
        let key_blob = key_entry
            .key_blob_info()
            .as_ref()
            .map(|(key_blob, _)| KeyBlob::Ref(key_blob))
            .ok_or(Error::Rc(ResponseCode::KEY_NOT_FOUND))
            .context(ks_err!("Missing key blob info."))?;
        let key_params = vec![
            KeyParameterValue::Algorithm(Algorithm::AES),
            KeyParameterValue::KeySize(256),
            KeyParameterValue::BlockMode(BlockMode::GCM),
            KeyParameterValue::PaddingMode(PaddingMode::NONE),
            KeyParameterValue::Nonce(self.nonce.clone()),
            KeyParameterValue::MacLength(128),
        ];
        let key_params: Vec<KmKeyParameter> = key_params.into_iter().map(|x| x.into()).collect();
        let key = ZVec::try_from(km_dev.use_key_in_one_step(
            db,
            key_id_guard,
            &key_blob,
            KeyPurpose::DECRYPT,
            &key_params,
            Some(auth_token),
            &self.ciphertext,
        )?)?;
        Ok(Arc::new(SuperKey { algorithm: self.algorithm, key, id: self.id, reencrypt_with }))
    }
}

/// Keys for unlocking UNLOCKED_DEVICE_REQUIRED keys, as LockedKeys, complete with
/// a database descriptor for the encrypting key and the sids for the auth tokens
/// that can be used to decrypt it.
struct BiometricUnlock {
    /// List of auth token SIDs that can be used to unlock these keys.
    sids: Vec<i64>,
    /// Database descriptor of key to use to unlock.
    key_desc: KeyDescriptor,
    /// Locked versions of the matching UserSuperKeys fields
    screen_lock_bound: LockedKey,
    screen_lock_bound_private: LockedKey,
}

#[derive(Default)]
struct UserSuperKeys {
    /// The per boot key is used for LSKF binding of authentication bound keys. There is one
    /// key per android user. The key is stored on flash encrypted with a key derived from a
    /// secret, that is itself derived from the user's lock screen knowledge factor (LSKF).
    /// When the user unlocks the device for the first time, this key is unlocked, i.e., decrypted,
    /// and stays memory resident until the device reboots.
    per_boot: Option<Arc<SuperKey>>,
    /// The screen lock key works like the per boot key with the distinction that it is cleared
    /// from memory when the screen lock is engaged.
    screen_lock_bound: Option<Arc<SuperKey>>,
    /// When the device is locked, screen-lock-bound keys can still be encrypted, using
    /// ECDH public-key encryption. This field holds the decryption private key.
    screen_lock_bound_private: Option<Arc<SuperKey>>,
    /// Versions of the above two keys, locked behind a biometric.
    biometric_unlock: Option<BiometricUnlock>,
}

#[derive(Default)]
struct SkmState {
    user_keys: HashMap<UserId, UserSuperKeys>,
    key_index: HashMap<i64, Weak<SuperKey>>,
    boot_level_key_cache: Option<Mutex<BootLevelKeyCache>>,
}

impl SkmState {
    fn add_key_to_key_index(&mut self, super_key: &Arc<SuperKey>) -> Result<()> {
        if let SuperKeyIdentifier::DatabaseId(id) = super_key.id {
            self.key_index.insert(id, Arc::downgrade(super_key));
            Ok(())
        } else {
            Err(Error::sys()).context(ks_err!("Cannot add key with ID {:?}", super_key.id))
        }
    }
}

#[derive(Default)]
pub struct SuperKeyManager {
    data: SkmState,
}

impl SuperKeyManager {
    pub fn set_up_boot_level_cache(skm: &Arc<RwLock<Self>>, db: &mut KeystoreDB) -> Result<()> {
        let mut skm_guard = skm.write().unwrap();
        if skm_guard.data.boot_level_key_cache.is_some() {
            log::info!("In set_up_boot_level_cache: called for a second time");
            return Ok(());
        }
        let level_zero_key =
            get_level_zero_key(db).context(ks_err!("get_level_zero_key failed"))?;
        skm_guard.data.boot_level_key_cache =
            Some(Mutex::new(BootLevelKeyCache::new(level_zero_key)));
        log::info!("Starting boot level watcher.");
        let clone = skm.clone();
        std::thread::spawn(move || {
            Self::watch_boot_level(clone)
                .unwrap_or_else(|e| log::error!("watch_boot_level failed:\n{:?}", e));
        });
        Ok(())
    }

    /// Watch the `keystore.boot_level` system property, and keep boot level up to date.
    /// Blocks waiting for system property changes, so must be run in its own thread.
    fn watch_boot_level(skm: Arc<RwLock<Self>>) -> Result<()> {
        let mut w = PropertyWatcher::new("keystore.boot_level")
            .context(ks_err!("PropertyWatcher::new failed"))?;
        loop {
            let level = w
                .read(|_n, v| v.parse::<usize>().map_err(std::convert::Into::into))
                .context(ks_err!("read of property failed"))?;

            // This scope limits the skm_guard life, so we don't hold the skm_guard while
            // waiting.
            {
                let mut skm_guard = skm.write().unwrap();
                let boot_level_key_cache = skm_guard
                    .data
                    .boot_level_key_cache
                    .as_mut()
                    .ok_or_else(Error::sys)
                    .context(ks_err!("Boot level cache not initialized"))?
                    .get_mut()
                    .unwrap();
                if level < MAX_MAX_BOOT_LEVEL {
                    log::info!("Read keystore.boot_level value {}", level);
                    boot_level_key_cache
                        .advance_boot_level(level)
                        .context(ks_err!("advance_boot_level failed"))?;
                } else {
                    log::info!(
                        "keystore.boot_level {} hits maximum {}, finishing.",
                        level,
                        MAX_MAX_BOOT_LEVEL
                    );
                    boot_level_key_cache.finish();
                    break;
                }
            }
            w.wait(None).context(ks_err!("property wait failed"))?;
        }
        Ok(())
    }

    pub fn level_accessible(&self, boot_level: i32) -> bool {
        self.data
            .boot_level_key_cache
            .as_ref()
            .map_or(false, |c| c.lock().unwrap().level_accessible(boot_level as usize))
    }

    pub fn forget_all_keys_for_user(&mut self, user: UserId) {
        self.data.user_keys.remove(&user);
    }

    fn install_per_boot_key_for_user(
        &mut self,
        user: UserId,
        super_key: Arc<SuperKey>,
    ) -> Result<()> {
        self.data
            .add_key_to_key_index(&super_key)
            .context(ks_err!("add_key_to_key_index failed"))?;
        self.data.user_keys.entry(user).or_default().per_boot = Some(super_key);
        Ok(())
    }

    fn lookup_key(&self, key_id: &SuperKeyIdentifier) -> Result<Option<Arc<SuperKey>>> {
        Ok(match key_id {
            SuperKeyIdentifier::DatabaseId(id) => {
                self.data.key_index.get(id).and_then(|k| k.upgrade())
            }
            SuperKeyIdentifier::BootLevel(level) => self
                .data
                .boot_level_key_cache
                .as_ref()
                .map(|b| b.lock().unwrap().aes_key(*level as usize))
                .transpose()
                .context(ks_err!("aes_key failed"))?
                .flatten()
                .map(|key| {
                    Arc::new(SuperKey {
                        algorithm: SuperEncryptionAlgorithm::Aes256Gcm,
                        key,
                        id: *key_id,
                        reencrypt_with: None,
                    })
                }),
        })
    }

    pub fn get_per_boot_key_by_user_id(
        &self,
        user_id: UserId,
    ) -> Option<Arc<dyn AesGcm + Send + Sync>> {
        self.get_per_boot_key_by_user_id_internal(user_id)
            .map(|sk| -> Arc<dyn AesGcm + Send + Sync> { sk })
    }

    fn get_per_boot_key_by_user_id_internal(&self, user_id: UserId) -> Option<Arc<SuperKey>> {
        self.data.user_keys.get(&user_id).and_then(|e| e.per_boot.as_ref().cloned())
    }

    /// Check if a given key is super-encrypted, from its metadata. If so, unwrap the key using
    /// the relevant super key.
    pub fn unwrap_key_if_required<'a>(
        &self,
        metadata: &BlobMetaData,
        blob: &'a [u8],
    ) -> Result<KeyBlob<'a>> {
        Ok(if let Some(key_id) = SuperKeyIdentifier::from_metadata(metadata) {
            let super_key = self
                .lookup_key(&key_id)
                .context(ks_err!("lookup_key failed"))?
                .ok_or(Error::Rc(ResponseCode::LOCKED))
                .context(ks_err!("Required super decryption key is not in memory."))?;
            KeyBlob::Sensitive {
                key: Self::unwrap_key_with_key(blob, metadata, &super_key)
                    .context(ks_err!("unwrap_key_with_key failed"))?,
                reencrypt_with: super_key.reencrypt_with.as_ref().unwrap_or(&super_key).clone(),
                force_reencrypt: super_key.reencrypt_with.is_some(),
            }
        } else {
            KeyBlob::Ref(blob)
        })
    }

    /// Unwraps an encrypted key blob given an encryption key.
    fn unwrap_key_with_key(blob: &[u8], metadata: &BlobMetaData, key: &SuperKey) -> Result<ZVec> {
        match key.algorithm {
            SuperEncryptionAlgorithm::Aes256Gcm => match (metadata.iv(), metadata.aead_tag()) {
                (Some(iv), Some(tag)) => {
                    key.decrypt(blob, iv, tag).context(ks_err!("Failed to decrypt the key blob."))
                }
                (iv, tag) => Err(Error::Rc(ResponseCode::VALUE_CORRUPTED)).context(ks_err!(
                    "Key has incomplete metadata. Present: iv: {}, aead_tag: {}.",
                    iv.is_some(),
                    tag.is_some(),
                )),
            },
            SuperEncryptionAlgorithm::EcdhP521 => {
                match (metadata.public_key(), metadata.salt(), metadata.iv(), metadata.aead_tag()) {
                    (Some(public_key), Some(salt), Some(iv), Some(aead_tag)) => {
                        ECDHPrivateKey::from_private_key(&key.key)
                            .and_then(|k| k.decrypt_message(public_key, salt, iv, blob, aead_tag))
                            .context(ks_err!("Failed to decrypt the key blob with ECDH."))
                    }
                    (public_key, salt, iv, aead_tag) => {
                        Err(Error::Rc(ResponseCode::VALUE_CORRUPTED)).context(ks_err!(
                            concat!(
                                "Key has incomplete metadata. ",
                                "Present: public_key: {}, salt: {}, iv: {}, aead_tag: {}."
                            ),
                            public_key.is_some(),
                            salt.is_some(),
                            iv.is_some(),
                            aead_tag.is_some(),
                        ))
                    }
                }
            }
        }
    }

    /// Checks if user has setup LSKF, even when super key cache is empty for the user.
    /// The reference to self is unused but it is required to prevent calling this function
    /// concurrently with skm state database changes.
    fn super_key_exists_in_db_for_user(
        &self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
    ) -> Result<bool> {
        let key_in_db = db
            .key_exists(Domain::APP, user_id as u64 as i64, USER_SUPER_KEY.alias, KeyType::Super)
            .context(ks_err!())?;

        if key_in_db {
            Ok(key_in_db)
        } else {
            legacy_importer.has_super_key(user_id).context(ks_err!("Trying to query legacy db."))
        }
    }

    // Helper function to populate super key cache from the super key blob loaded from the database.
    fn populate_cache_from_super_key_blob(
        &mut self,
        user_id: UserId,
        algorithm: SuperEncryptionAlgorithm,
        entry: KeyEntry,
        pw: &Password,
    ) -> Result<Arc<SuperKey>> {
        let super_key = Self::extract_super_key_from_key_entry(algorithm, entry, pw, None)
            .context(ks_err!("Failed to extract super key from key entry"))?;
        self.install_per_boot_key_for_user(user_id, super_key.clone())?;
        Ok(super_key)
    }

    /// Extracts super key from the entry loaded from the database.
    pub fn extract_super_key_from_key_entry(
        algorithm: SuperEncryptionAlgorithm,
        entry: KeyEntry,
        pw: &Password,
        reencrypt_with: Option<Arc<SuperKey>>,
    ) -> Result<Arc<SuperKey>> {
        if let Some((blob, metadata)) = entry.key_blob_info() {
            let key = match (
                metadata.encrypted_by(),
                metadata.salt(),
                metadata.iv(),
                metadata.aead_tag(),
            ) {
                (Some(&EncryptedBy::Password), Some(salt), Some(iv), Some(tag)) => {
                    // Note that password encryption is AES no matter the value of algorithm.
                    let key = pw
                        .derive_key(salt, AES_256_KEY_LENGTH)
                        .context(ks_err!("Failed to generate key from password."))?;

                    aes_gcm_decrypt(blob, iv, tag, &key)
                        .context(ks_err!("Failed to decrypt key blob."))?
                }
                (enc_by, salt, iv, tag) => {
                    return Err(Error::Rc(ResponseCode::VALUE_CORRUPTED)).context(ks_err!(
                        concat!(
                            "Super key has incomplete metadata.",
                            "encrypted_by: {:?}; Present: salt: {}, iv: {}, aead_tag: {}."
                        ),
                        enc_by,
                        salt.is_some(),
                        iv.is_some(),
                        tag.is_some()
                    ));
                }
            };
            Ok(Arc::new(SuperKey {
                algorithm,
                key,
                id: SuperKeyIdentifier::DatabaseId(entry.id()),
                reencrypt_with,
            }))
        } else {
            Err(Error::Rc(ResponseCode::VALUE_CORRUPTED)).context(ks_err!("No key blob info."))
        }
    }

    /// Encrypts the super key from a key derived from the password, before storing in the database.
    pub fn encrypt_with_password(
        super_key: &[u8],
        pw: &Password,
    ) -> Result<(Vec<u8>, BlobMetaData)> {
        let salt = generate_salt().context("In encrypt_with_password: Failed to generate salt.")?;
        let derived_key = pw
            .derive_key(&salt, AES_256_KEY_LENGTH)
            .context(ks_err!("Failed to derive password."))?;
        let mut metadata = BlobMetaData::new();
        metadata.add(BlobMetaEntry::EncryptedBy(EncryptedBy::Password));
        metadata.add(BlobMetaEntry::Salt(salt));
        let (encrypted_key, iv, tag) = aes_gcm_encrypt(super_key, &derived_key)
            .context(ks_err!("Failed to encrypt new super key."))?;
        metadata.add(BlobMetaEntry::Iv(iv));
        metadata.add(BlobMetaEntry::AeadTag(tag));
        Ok((encrypted_key, metadata))
    }

    // Helper function to encrypt a key with the given super key. Callers should select which super
    // key to be used. This is called when a key is super encrypted at its creation as well as at
    // its upgrade.
    fn encrypt_with_aes_super_key(
        key_blob: &[u8],
        super_key: &SuperKey,
    ) -> Result<(Vec<u8>, BlobMetaData)> {
        if super_key.algorithm != SuperEncryptionAlgorithm::Aes256Gcm {
            return Err(Error::sys()).context(ks_err!("unexpected algorithm"));
        }
        let mut metadata = BlobMetaData::new();
        let (encrypted_key, iv, tag) = aes_gcm_encrypt(key_blob, &(super_key.key))
            .context(ks_err!("Failed to encrypt new super key."))?;
        metadata.add(BlobMetaEntry::Iv(iv));
        metadata.add(BlobMetaEntry::AeadTag(tag));
        super_key.id.add_to_metadata(&mut metadata);
        Ok((encrypted_key, metadata))
    }

    // Encrypts a given key_blob using a hybrid approach, which can either use the symmetric super
    // key or the public super key depending on which is available.
    //
    // If the symmetric_key is available, the key_blob is encrypted using symmetric encryption with
    // the provided symmetric super key.  Otherwise, the function loads the public super key from
    // the KeystoreDB and encrypts the key_blob using ECDH encryption and marks the keyblob to be
    // re-encrypted with the symmetric super key on the first use.
    //
    // This hybrid scheme allows lock-screen-bound keys to be added when the screen is locked.
    fn encrypt_with_hybrid_super_key(
        key_blob: &[u8],
        symmetric_key: Option<&SuperKey>,
        public_key_type: &SuperKeyType,
        db: &mut KeystoreDB,
        user_id: UserId,
    ) -> Result<(Vec<u8>, BlobMetaData)> {
        if let Some(super_key) = symmetric_key {
            Self::encrypt_with_aes_super_key(key_blob, super_key)
                .context(ks_err!("Failed to encrypt with ScreenLockBound super key."))
        } else {
            // Symmetric key is not available, use public key encryption
            let loaded = db
                .load_super_key(public_key_type, user_id)
                .context(ks_err!("load_super_key failed."))?;
            let (key_id_guard, key_entry) =
                loaded.ok_or_else(Error::sys).context(ks_err!("User ECDH super key missing."))?;
            let public_key = key_entry
                .metadata()
                .sec1_public_key()
                .ok_or_else(Error::sys)
                .context(ks_err!("sec1_public_key missing."))?;
            let mut metadata = BlobMetaData::new();
            let (ephem_key, salt, iv, encrypted_key, aead_tag) =
                ECDHPrivateKey::encrypt_message(public_key, key_blob)
                    .context(ks_err!("ECDHPrivateKey::encrypt_message failed."))?;
            metadata.add(BlobMetaEntry::PublicKey(ephem_key));
            metadata.add(BlobMetaEntry::Salt(salt));
            metadata.add(BlobMetaEntry::Iv(iv));
            metadata.add(BlobMetaEntry::AeadTag(aead_tag));
            SuperKeyIdentifier::DatabaseId(key_id_guard.id()).add_to_metadata(&mut metadata);
            Ok((encrypted_key, metadata))
        }
    }

    /// Check if super encryption is required and if so, super-encrypt the key to be stored in
    /// the database.
    #[allow(clippy::too_many_arguments)]
    pub fn handle_super_encryption_on_key_init(
        &self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        domain: &Domain,
        key_parameters: &[KeyParameter],
        flags: Option<i32>,
        user_id: UserId,
        key_blob: &[u8],
    ) -> Result<(Vec<u8>, BlobMetaData)> {
        match Enforcements::super_encryption_required(domain, key_parameters, flags) {
            SuperEncryptionType::None => Ok((key_blob.to_vec(), BlobMetaData::new())),
            SuperEncryptionType::LskfBound => {
                // Encrypt the given key blob with the user's per-boot super key.  If the per-boot
                // super key is not unlocked or the LSKF is not setup, an error is returned.
                match self
                    .get_user_state(db, legacy_importer, user_id)
                    .context(ks_err!("Failed to get user state."))?
                {
                    UserState::LskfUnlocked(super_key) => {
                        Self::encrypt_with_aes_super_key(key_blob, &super_key)
                            .context(ks_err!("Failed to encrypt with LskfBound key."))
                    }
                    UserState::LskfLocked => {
                        Err(Error::Rc(ResponseCode::LOCKED)).context(ks_err!("Device is locked."))
                    }
                    UserState::Uninitialized => Err(Error::Rc(ResponseCode::UNINITIALIZED))
                        .context(ks_err!("LSKF is not setup for the user.")),
                }
            }
            SuperEncryptionType::ScreenLockBound => {
                let screen_lock_bound_symmetric_key = self
                    .data
                    .user_keys
                    .get(&user_id)
                    .and_then(|e| e.screen_lock_bound.as_ref())
                    .map(|arc| arc.as_ref());
                Self::encrypt_with_hybrid_super_key(
                    key_blob,
                    screen_lock_bound_symmetric_key,
                    &USER_SCREEN_LOCK_BOUND_P521_KEY,
                    db,
                    user_id,
                )
                .context(ks_err!("Failed to encrypt with ScreenLockBound hybrid scheme."))
            }
            SuperEncryptionType::BootLevel(level) => {
                let key_id = SuperKeyIdentifier::BootLevel(level);
                let super_key = self
                    .lookup_key(&key_id)
                    .context(ks_err!("lookup_key failed"))?
                    .ok_or(Error::Rc(ResponseCode::LOCKED))
                    .context(ks_err!("Boot stage key absent"))?;
                Self::encrypt_with_aes_super_key(key_blob, &super_key)
                    .context(ks_err!("Failed to encrypt with BootLevel key."))
            }
        }
    }

    /// Check if a given key needs re-super-encryption, from its KeyBlob type.
    /// If so, re-super-encrypt the key and return a new set of metadata,
    /// containing the new super encryption information.
    pub fn reencrypt_if_required<'a>(
        key_blob_before_upgrade: &KeyBlob,
        key_after_upgrade: &'a [u8],
    ) -> Result<(KeyBlob<'a>, Option<BlobMetaData>)> {
        match key_blob_before_upgrade {
            KeyBlob::Sensitive { reencrypt_with: super_key, .. } => {
                let (key, metadata) =
                    Self::encrypt_with_aes_super_key(key_after_upgrade, super_key)
                        .context(ks_err!("Failed to re-super-encrypt key."))?;
                Ok((KeyBlob::NonSensitive(key), Some(metadata)))
            }
            _ => Ok((KeyBlob::Ref(key_after_upgrade), None)),
        }
    }

    /// Fetch a superencryption key from the database, or create it if it doesn't already exist.
    /// When this is called, the caller must hold the lock on the SuperKeyManager.
    /// So it's OK that the check and creation are different DB transactions.
    fn get_or_create_super_key(
        &mut self,
        db: &mut KeystoreDB,
        user_id: UserId,
        key_type: &SuperKeyType,
        password: &Password,
        reencrypt_with: Option<Arc<SuperKey>>,
    ) -> Result<Arc<SuperKey>> {
        let loaded_key = db.load_super_key(key_type, user_id)?;
        if let Some((_, key_entry)) = loaded_key {
            Ok(Self::extract_super_key_from_key_entry(
                key_type.algorithm,
                key_entry,
                password,
                reencrypt_with,
            )?)
        } else {
            let (super_key, public_key) = match key_type.algorithm {
                SuperEncryptionAlgorithm::Aes256Gcm => (
                    generate_aes256_key().context(ks_err!("Failed to generate AES 256 key."))?,
                    None,
                ),
                SuperEncryptionAlgorithm::EcdhP521 => {
                    let key = ECDHPrivateKey::generate()
                        .context(ks_err!("Failed to generate ECDH key"))?;
                    (
                        key.private_key().context(ks_err!("private_key failed"))?,
                        Some(key.public_key().context(ks_err!("public_key failed"))?),
                    )
                }
            };
            // Derive an AES256 key from the password and re-encrypt the super key
            // before we insert it in the database.
            let (encrypted_super_key, blob_metadata) =
                Self::encrypt_with_password(&super_key, password).context(ks_err!())?;
            let mut key_metadata = KeyMetaData::new();
            if let Some(pk) = public_key {
                key_metadata.add(KeyMetaEntry::Sec1PublicKey(pk));
            }
            let key_entry = db
                .store_super_key(
                    user_id,
                    key_type,
                    &encrypted_super_key,
                    &blob_metadata,
                    &key_metadata,
                )
                .context(ks_err!("Failed to store super key."))?;
            Ok(Arc::new(SuperKey {
                algorithm: key_type.algorithm,
                key: super_key,
                id: SuperKeyIdentifier::DatabaseId(key_entry.id()),
                reencrypt_with,
            }))
        }
    }

    /// Decrypt the screen-lock bound keys for this user using the password and store in memory.
    pub fn unlock_screen_lock_bound_key(
        &mut self,
        db: &mut KeystoreDB,
        user_id: UserId,
        password: &Password,
    ) -> Result<()> {
        let (screen_lock_bound, screen_lock_bound_private) = self
            .data
            .user_keys
            .get(&user_id)
            .map(|e| (e.screen_lock_bound.clone(), e.screen_lock_bound_private.clone()))
            .unwrap_or((None, None));

        if screen_lock_bound.is_some() && screen_lock_bound_private.is_some() {
            // Already unlocked.
            return Ok(());
        }

        let aes = if let Some(screen_lock_bound) = screen_lock_bound {
            // This is weird. If this point is reached only one of the screen locked keys was
            // initialized. This should never happen.
            screen_lock_bound
        } else {
            self.get_or_create_super_key(db, user_id, &USER_SCREEN_LOCK_BOUND_KEY, password, None)
                .context(ks_err!("Trying to get or create symmetric key."))?
        };

        let ecdh = if let Some(screen_lock_bound_private) = screen_lock_bound_private {
            // This is weird. If this point is reached only one of the screen locked keys was
            // initialized. This should never happen.
            screen_lock_bound_private
        } else {
            self.get_or_create_super_key(
                db,
                user_id,
                &USER_SCREEN_LOCK_BOUND_P521_KEY,
                password,
                Some(aes.clone()),
            )
            .context(ks_err!("Trying to get or create asymmetric key."))?
        };

        self.data.add_key_to_key_index(&aes)?;
        self.data.add_key_to_key_index(&ecdh)?;
        let entry = self.data.user_keys.entry(user_id).or_default();
        entry.screen_lock_bound = Some(aes);
        entry.screen_lock_bound_private = Some(ecdh);
        Ok(())
    }

    /// Wipe the screen-lock bound keys for this user from memory.
    pub fn lock_screen_lock_bound_key(
        &mut self,
        db: &mut KeystoreDB,
        user_id: UserId,
        unlocking_sids: &[i64],
    ) {
        log::info!("Locking screen bound for user {} sids {:?}", user_id, unlocking_sids);
        let mut entry = self.data.user_keys.entry(user_id).or_default();
        if !unlocking_sids.is_empty() {
            if let (Some(aes), Some(ecdh)) = (
                entry.screen_lock_bound.as_ref().cloned(),
                entry.screen_lock_bound_private.as_ref().cloned(),
            ) {
                let res = (|| -> Result<()> {
                    let key_desc = KeyMintDevice::internal_descriptor(format!(
                        "biometric_unlock_key_{}",
                        user_id
                    ));
                    let encrypting_key = generate_aes256_key()?;
                    let km_dev: KeyMintDevice =
                        KeyMintDevice::get(SecurityLevel::TRUSTED_ENVIRONMENT)
                            .context(ks_err!("KeyMintDevice::get failed"))?;
                    let mut key_params = vec![
                        KeyParameterValue::Algorithm(Algorithm::AES),
                        KeyParameterValue::KeySize(256),
                        KeyParameterValue::BlockMode(BlockMode::GCM),
                        KeyParameterValue::PaddingMode(PaddingMode::NONE),
                        KeyParameterValue::CallerNonce,
                        KeyParameterValue::KeyPurpose(KeyPurpose::DECRYPT),
                        KeyParameterValue::MinMacLength(128),
                        KeyParameterValue::AuthTimeout(BIOMETRIC_AUTH_TIMEOUT_S),
                        KeyParameterValue::HardwareAuthenticatorType(
                            HardwareAuthenticatorType::FINGERPRINT,
                        ),
                    ];
                    for sid in unlocking_sids {
                        key_params.push(KeyParameterValue::UserSecureID(*sid));
                    }
                    let key_params: Vec<KmKeyParameter> =
                        key_params.into_iter().map(|x| x.into()).collect();
                    km_dev.create_and_store_key(
                        db,
                        &key_desc,
                        KeyType::Client, /* TODO Should be Super b/189470584 */
                        |dev| {
                            let _wp = wd::watch_millis(
                                "In lock_screen_lock_bound_key: calling importKey.",
                                500,
                            );
                            dev.importKey(
                                key_params.as_slice(),
                                KeyFormat::RAW,
                                &encrypting_key,
                                None,
                            )
                        },
                    )?;
                    entry.biometric_unlock = Some(BiometricUnlock {
                        sids: unlocking_sids.into(),
                        key_desc,
                        screen_lock_bound: LockedKey::new(&encrypting_key, &aes)?,
                        screen_lock_bound_private: LockedKey::new(&encrypting_key, &ecdh)?,
                    });
                    Ok(())
                })();
                // There is no reason to propagate an error here upwards. We must discard
                // entry.screen_lock_bound* in any case.
                if let Err(e) = res {
                    log::error!("Error setting up biometric unlock: {:#?}", e);
                }
            }
        }
        entry.screen_lock_bound = None;
        entry.screen_lock_bound_private = None;
    }

    /// User has unlocked, not using a password. See if any of our stored auth tokens can be used
    /// to unlock the keys protecting UNLOCKED_DEVICE_REQUIRED keys.
    pub fn try_unlock_user_with_biometric(
        &mut self,
        db: &mut KeystoreDB,
        user_id: UserId,
    ) -> Result<()> {
        let mut entry = self.data.user_keys.entry(user_id).or_default();
        if let Some(biometric) = entry.biometric_unlock.as_ref() {
            let (key_id_guard, key_entry) = db
                .load_key_entry(
                    &biometric.key_desc,
                    KeyType::Client, // This should not be a Client key.
                    KeyEntryLoadBits::KM,
                    AID_KEYSTORE,
                    |_, _| Ok(()),
                )
                .context(ks_err!("load_key_entry failed"))?;
            let km_dev: KeyMintDevice = KeyMintDevice::get(SecurityLevel::TRUSTED_ENVIRONMENT)
                .context(ks_err!("KeyMintDevice::get failed"))?;
            for sid in &biometric.sids {
                if let Some((auth_token_entry, _)) = db.find_auth_token_entry(|entry| {
                    entry.auth_token().userId == *sid || entry.auth_token().authenticatorId == *sid
                }) {
                    let res: Result<(Arc<SuperKey>, Arc<SuperKey>)> = (|| {
                        let slb = biometric.screen_lock_bound.decrypt(
                            db,
                            &km_dev,
                            &key_id_guard,
                            &key_entry,
                            auth_token_entry.auth_token(),
                            None,
                        )?;
                        let slbp = biometric.screen_lock_bound_private.decrypt(
                            db,
                            &km_dev,
                            &key_id_guard,
                            &key_entry,
                            auth_token_entry.auth_token(),
                            Some(slb.clone()),
                        )?;
                        Ok((slb, slbp))
                    })();
                    match res {
                        Ok((slb, slbp)) => {
                            entry.screen_lock_bound = Some(slb.clone());
                            entry.screen_lock_bound_private = Some(slbp.clone());
                            self.data.add_key_to_key_index(&slb)?;
                            self.data.add_key_to_key_index(&slbp)?;
                            log::info!("Successfully unlocked with biometric");
                            return Ok(());
                        }
                        Err(e) => {
                            log::warn!("attempt failed: {:?}", e)
                        }
                    }
                }
            }
        }
        Ok(())
    }

    /// Returns the keystore locked state of the given user. It requires the thread local
    /// keystore database and a reference to the legacy migrator because it may need to
    /// import the super key from the legacy blob database to the keystore database.
    pub fn get_user_state(
        &self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
    ) -> Result<UserState> {
        match self.get_per_boot_key_by_user_id_internal(user_id) {
            Some(super_key) => Ok(UserState::LskfUnlocked(super_key)),
            None => {
                // Check if a super key exists in the database or legacy database.
                // If so, return locked user state.
                if self
                    .super_key_exists_in_db_for_user(db, legacy_importer, user_id)
                    .context(ks_err!())?
                {
                    Ok(UserState::LskfLocked)
                } else {
                    Ok(UserState::Uninitialized)
                }
            }
        }
    }

    /// Deletes all keys and super keys for the given user.
    /// This is called when a user is deleted.
    pub fn remove_user(
        &mut self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
    ) -> Result<()> {
        // Mark keys created on behalf of the user as unreferenced.
        legacy_importer
            .bulk_delete_user(user_id, false)
            .context(ks_err!("Trying to delete legacy keys."))?;
        db.unbind_keys_for_user(user_id, false).context(ks_err!("Error in unbinding keys."))?;

        // Delete super key in cache, if exists.
        self.forget_all_keys_for_user(user_id);
        Ok(())
    }

    /// Deletes all authentication bound keys and super keys for the given user.  The user must be
    /// unlocked before this function is called.  This function is used to transition a user to
    /// swipe.
    pub fn reset_user(
        &mut self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
    ) -> Result<()> {
        match self.get_user_state(db, legacy_importer, user_id)? {
            UserState::Uninitialized => {
                Err(Error::sys()).context(ks_err!("Tried to reset an uninitialized user!"))
            }
            UserState::LskfLocked => {
                Err(Error::sys()).context(ks_err!("Tried to reset a locked user's password!"))
            }
            UserState::LskfUnlocked(_) => {
                // Mark keys created on behalf of the user as unreferenced.
                legacy_importer
                    .bulk_delete_user(user_id, true)
                    .context(ks_err!("Trying to delete legacy keys."))?;
                db.unbind_keys_for_user(user_id, true)
                    .context(ks_err!("Error in unbinding keys."))?;

                // Delete super key in cache, if exists.
                self.forget_all_keys_for_user(user_id);
                Ok(())
            }
        }
    }

    /// If the user hasn't been initialized yet, then this function generates the user's super keys
    /// and sets the user's state to LskfUnlocked.  Otherwise this function returns an error.
    pub fn init_user(
        &mut self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
        password: &Password,
    ) -> Result<()> {
        match self.get_user_state(db, legacy_importer, user_id)? {
            UserState::LskfUnlocked(_) | UserState::LskfLocked => {
                Err(Error::sys()).context(ks_err!("Tried to re-init an initialized user!"))
            }
            UserState::Uninitialized => {
                // Generate a new super key.
                let super_key =
                    generate_aes256_key().context(ks_err!("Failed to generate AES 256 key."))?;
                // Derive an AES256 key from the password and re-encrypt the super key
                // before we insert it in the database.
                let (encrypted_super_key, blob_metadata) =
                    Self::encrypt_with_password(&super_key, password)
                        .context(ks_err!("Failed to encrypt super key with password!"))?;

                let key_entry = db
                    .store_super_key(
                        user_id,
                        &USER_SUPER_KEY,
                        &encrypted_super_key,
                        &blob_metadata,
                        &KeyMetaData::new(),
                    )
                    .context(ks_err!("Failed to store super key."))?;

                self.populate_cache_from_super_key_blob(
                    user_id,
                    USER_SUPER_KEY.algorithm,
                    key_entry,
                    password,
                )
                .context(ks_err!("Failed to initialize user!"))?;
                Ok(())
            }
        }
    }

    /// Unlocks the given user with the given password.
    ///
    /// If the user is LskfLocked:
    /// - Unlock the per_boot super key
    /// - Unlock the screen_lock_bound super key
    ///
    /// If the user is LskfUnlocked:
    /// - Unlock the screen_lock_bound super key only
    ///
    pub fn unlock_user(
        &mut self,
        db: &mut KeystoreDB,
        legacy_importer: &LegacyImporter,
        user_id: UserId,
        password: &Password,
    ) -> Result<()> {
        match self.get_user_state(db, legacy_importer, user_id)? {
            UserState::LskfUnlocked(_) => self.unlock_screen_lock_bound_key(db, user_id, password),
            UserState::Uninitialized => {
                Err(Error::sys()).context(ks_err!("Tried to unlock an uninitialized user!"))
            }
            UserState::LskfLocked => {
                let alias = &USER_SUPER_KEY;
                let result = legacy_importer
                    .with_try_import_super_key(user_id, password, || {
                        db.load_super_key(alias, user_id)
                    })
                    .context(ks_err!("Failed to load super key"))?;

                match result {
                    Some((_, entry)) => {
                        self.populate_cache_from_super_key_blob(
                            user_id,
                            alias.algorithm,
                            entry,
                            password,
                        )
                        .context(ks_err!("Failed when unlocking user."))?;
                        self.unlock_screen_lock_bound_key(db, user_id, password)
                    }
                    None => {
                        Err(Error::sys()).context(ks_err!("Locked user does not have a super key!"))
                    }
                }
            }
        }
    }
}

/// This enum represents different states of the user's life cycle in the device.
/// For now, only three states are defined. More states may be added later.
pub enum UserState {
    // The user has registered LSKF and has unlocked the device by entering PIN/Password,
    // and hence the per-boot super key is available in the cache.
    LskfUnlocked(Arc<SuperKey>),
    // The user has registered LSKF, but has not unlocked the device using password, after reboot.
    // Hence the per-boot super-key(s) is not available in the cache.
    // However, the encrypted super key is available in the database.
    LskfLocked,
    // There's no user in the device for the given user id, or the user with the user id has not
    // setup LSKF.
    Uninitialized,
}

/// This enum represents three states a KeyMint Blob can be in, w.r.t super encryption.
/// `Sensitive` holds the non encrypted key and a reference to its super key.
/// `NonSensitive` holds a non encrypted key that is never supposed to be encrypted.
/// `Ref` holds a reference to a key blob when it does not need to be modified if its
/// life time allows it.
pub enum KeyBlob<'a> {
    Sensitive {
        key: ZVec,
        /// If KeyMint reports that the key must be upgraded, we must
        /// re-encrypt the key before writing to the database; we use
        /// this key.
        reencrypt_with: Arc<SuperKey>,
        /// If this key was decrypted with an ECDH key, we want to
        /// re-encrypt it on first use whether it was upgraded or not;
        /// this field indicates that that's necessary.
        force_reencrypt: bool,
    },
    NonSensitive(Vec<u8>),
    Ref(&'a [u8]),
}

impl<'a> KeyBlob<'a> {
    pub fn force_reencrypt(&self) -> bool {
        if let KeyBlob::Sensitive { force_reencrypt, .. } = self {
            *force_reencrypt
        } else {
            false
        }
    }
}

/// Deref returns a reference to the key material in any variant.
impl<'a> Deref for KeyBlob<'a> {
    type Target = [u8];

    fn deref(&self) -> &Self::Target {
        match self {
            Self::Sensitive { key, .. } => key,
            Self::NonSensitive(key) => key,
            Self::Ref(key) => key,
        }
    }
}