At-Rest Encryption for Complete Data Protection

Many developers using hosted database solutions like Amazon RDS or Microsoft Azure are familiar with the “encrypt at rest” checkbox provided by their host. This will provide a modicum of security, but only defends your data against a narrow set of potential threats. Instead, we’ll discuss both the threats this feature does and does not protect against and some practical approaches to handling the uncovered edge cases. Attendees will learn how their application can both encrypt and decrypt data before communicating with an external data store for complete data protection.

Transcript

1. At-Rest Encryption for
   Complete Data
   Protection
   Eric Mann
   

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2. Let’s build a web
   application. Let’s
   make it secure.
   

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3. Data Classification Tiers
   Tier 1 - Unrestricted Data
   Tier 2 - Confidential Data
   Tier 3 - Highly Secured Data
   Tier 4 - Restricted Data
   

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4. (Full image slide with caption)
   STRIDE Threat Modeling -
   https://resources.infosecinstitute.com/threat-modeling-finding-defects-early-in-the-cycle/
   

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5. (Full image slide with caption)
   Image credit: https://movieweb.com/
   

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6. DREAD Risk Ratings
   Score each of the following from 1-10
   ● Damage Potential
   ● Reproducibility
   ● Exploitability
   ● Affected Users
   ● Discoverability
   

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7. DREAD Risk Ratings
   D R E A D Rate
   Credentials sniffed from
   the network
   10 10 5 5 5 7
   SQL commands injected
   in the front-end
   10 10 10 10 5 9
   Arbitrary file navigation
   and download on the
   10 10 10 5 0 7
   

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8. In Transit
   Encrypting communication
   between two parties over a
   (potentially) insecure
   medium.
   At Rest
   Encrypting data used by a single
   party between to periods of
   time.
   Data Encryption
   

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9. (Full image slide. No text)
   

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10. At-Rest Encryption
    1. Protects data written out
    to disk
    2. Transparent to the application
    layer
    3. (Usually) Provided by hosted
    DB solutions
    4. (Often) Required for regulatory
    compliance
    

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11. (Full image slide with caption)
    Tom Cruise in "Mission: Impossible — Rogue Nation." YouTube/Paramount
    

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12. Application-level Encryption
    By allowing the application to manage its own encryption keys, the
    crypto operations lift up into the application stack itself. The database
    engine can’t read or manage the data, neither can any other process in
    memory.
    Your data’s security then relies on the security of your application’s
    authentication and access control systems.
    

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13. Application-level Encryption
    By allowing the application to manage its own encryption keys, the
    crypto operations lift up into the application stack itself. The database
    engine can’t read or manage the data, neither can any other process in
    memory.
    Your data’s security then relies on the security of your application’s
    authentication and access control systems.
    

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14. To store encrypted
    data and still search
    the plaintext, we
    need a blind index.
    

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15. Blind Index
    Store a keyed hash of the data in one column
    Store the encrypted data in a separate column
    Be sure to use separate hashing and encryption keys!
    

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16. Blind Index
    CREATE TABLE reviews (
    id INT NOT NULL,
    title TEXT NOT NULL, /* encrypted */
    review TEXT NOT NULL, /* encrypted */
    reviewer TEXT NOT NULL, /* encrypted */
    reviewer_idx TEXT NOT NULL, /* blind index */
    PRIMARY KEY (id)
    );
    CREATE INDEX ON reviews (reviewer_idx);
    

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17. class Review {
    public int $id;
    public string $title;
    public string $review;
    public string $reviewer;
    }
    interface ReviewDatabase {
    function create(Review $review);
    function get(string $reviewId);
    function update(Review $review);
    function delete(string $reviewId);
    }
    

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18. class PlaintextDatabase implements ReviewDatabase {
    private $db;
    function __construct(PDO $db)
    {
    $this->db = $db;
    }
    function create(Review $review)
    {
    $statement = $this->db->prepare("INSERT INTO reviews (title, review, reviewer) VALUES (:title,
    :review, :reviewer)");
    $statement->bindParam(':title', $review->title);
    $statement->bindParam(':review', $review->review);
    $statement->bindParam(':reviewer', $review->reviewer);
    $statement->execute();
    }
    // ...
    

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19. class PlaintextDatabase implements ReviewDatabase {
    // ...
    function get(string $reviewId)
    {
    $statement = $this->db->prepare("SELECT * FROM reviews WHERE id = :id LIMIT 0, 1")
    $statement->bindParam(':id', $reviewId);
    while ($review = $statement->fetch()) {
    return new Review($review);
    }
    return null;
    }
    // ... and so on
    }
    

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20. Let’s add crypto...
    

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21. class EncryptedDatabase implements ReviewDatabase {
    private $db;
    private $key
    function __construct(PDO $db, string $key)
    {
    $this->db = $db;
    $this->key = $key;
    }
    // ...
    

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22. class EncryptedDatabase implements ReviewDatabase {
    // ...
    private function encryptString(string $plaintext)
    {
    $block_size = 16;
    $nonce = random_bytes(SODIUM_CRYPTO_SECRETBOX_NONCE_BYTES);
    $message = sodium_pad($plaintext, $block_size);
    // Return the nonce and the encrypted messsage
    return bin2hex($nonce . sodium_crypto_secretbox($message, $nonce, $this->key));
    }
    private function decryptString(string $ciphertext)
    {
    $block_size = 16;
    $nonce = substr(hex2bin($ciphertext), 0, SODIUM_CRYPTO_SECRETBOX_NONCE_BYTES);
    $message = substr(hex2bin($ciphertext), SODIUM_CRYPTO_SECRETBOX_NONCE_BYTES);
    $message = sodium_crypto_secretbox_open($encrypted, $nonce, $this->key);
    return sodium_unpad($message, $block_size);
    }
    // ...
    

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23. class EncryptedDatabase implements ReviewDatabase {
    // ...
    function create(Review $review)
    {
    $statement = $this->db->prepare("INSERT INTO reviews (title, review, reviewer) VALUES (:title,
    :review, :reviewer)");
    $statement->bindParam(':title', encryptString($review->title));
    $statement->bindParam(':review', encryptString($review->review));
    $statement->bindParam(':reviewer', encryptString($review->reviewer));
    $statement->execute();
    }
    // ...
    

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24. class EncryptedDatabase implements ReviewDatabase {
    // ...
    function get(string $reviewId)
    {
    $statement = $this->db->prepare("SELECT * FROM reviews WHERE id = :id LIMIT 0, 1")
    $statement->bindParam(':id', $reviewId);
    while ($review = $statement->fetch()) {
    return new Review([
    "id" => $review["id"],
    "title" => decryptString($review["title"]),
    "review" => decryptString($review["review"]),
    "reviewer" => decryptString($review["reviewer"])
    ]);
    }
    return null;
    }
    // ... and so on
    }
    

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25. Let’s add an index...
    

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26. class EncryptedDatabase implements ReviewDatabase {
    private $db;
    private $key
    private $hmac_keys;
    function __construct(PDO $db, string $key, array $hmac_keys)
    {
    $this->db = $db;
    $this->key = $key;
    $this->hmac_keys = $hmac_keys;
    }
    // ...
    

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27. class EncryptedDatabase implements ReviewDatabase {
    // ...
    function hashIndex($value, $index)
    {
    $hmac_key = $this->hmac_keys[$index];
    return hash_hmac('sha256', $value, $hmac_key);
    }
    function create(Review $review)
    {
    $statement = $this->db->prepare("INSERT INTO reviews (title, review, reviewer) VALUES (:title,
    :review, :reviewer, :reviewer_idx)");
    $statement->bindParam(':title', encryptString($review->title));
    $statement->bindParam(':review', encryptString($review->review));
    $statement->bindParam(':reviewer', encryptString($review->reviewer));
    $statement->bindParam(':reviewer_idx', hashIndex($review->reviewer, 'reviewer'));
    $statement->execute();
    }
    // ... and so on
    }
    

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28. class EncryptedDatabase implements ReviewDatabase {
    // ...
    function getAllByReviwer(string $reviewer)
    {
    $reviewerIdx = hashIndex($reviewer, 'reviewer');
    $statement = $this->db->prepare("SELECT * FROM reviews WHERE reviewer_idx = :id")
    $statement->bindParam(':idx', $reviewerIdx);
    $reviews = [];
    while ($review = $statement->fetch()) {
    $records[] = new Review([
    "id" => $review["id"],
    "title" => decryptString($review["title"]),
    "review" => decryptString($review["review"]),
    "reviewer" => decryptString($review["reviewer"])
    ]);
    }
    return $reviews;
    }
    // ...
    }
    

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29. Take a deep breath
    

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30. (Full image slide with caption)
    CipherSweet by Paragon Initiative Enterprsies: Fast, searchable field-level encryption for PHP
    projects
    

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31. Application-level Encryption
    By allowing the application to manage its own encryption keys, the
    crypto operations lift up into the application stack itself. The database
    engine can’t read or manage the data, neither can any other process in
    memory.
    Your data’s security then relies on the security of your application’s
    authentication and access control systems.
    

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32. (Full image slide with caption)
    Tom Cruise in "Mission: Impossible." Paramount
    

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33. Defense-in-Depth
    1. Evaluate threat models
    2. Encrypt in transit
    3. Encrypt at rest
    4. Limit access to keys
    5. GOTO 1
    

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34. Frequent Questions
    How do I query the database directly?
    How do I debug the system?
    What data really needs to be encrypted?
    Does CipherSweet work for more than just PHP?
    

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35. Questions?
    

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36. Thank you
    eric.mann@vacasa.com | 503.925.6266
    

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