At-Rest Encryption for Complete Data Protection

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.

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Eric Mann

May 21, 2019
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  1. 3.

    Data Classification Tiers Tier 1 - Unrestricted Data Tier 2

    - Confidential Data Tier 3 - Highly Secured Data Tier 4 - Restricted Data
  2. 6.

    DREAD Risk Ratings Score each of the following from 1-10

    • Damage Potential • Reproducibility • Exploitability • Affected Users • Discoverability
  3. 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
  4. 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
  5. 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
  6. 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.
  7. 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.
  8. 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!
  9. 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);
  10. 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); }
  11. 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(); } // ...
  12. 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 }
  13. 21.

    class EncryptedDatabase implements ReviewDatabase { private $db; private $key function

    __construct(PDO $db, string $key) { $this->db = $db; $this->key = $key; } // ...
  14. 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); } // ...
  15. 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(); } // ...
  16. 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 }
  17. 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; } // ...
  18. 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 }
  19. 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; } // ... }
  20. 30.

    (Full image slide with caption) CipherSweet by Paragon Initiative Enterprsies:

    Fast, searchable field-level encryption for PHP projects
  21. 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.
  22. 33.

    Defense-in-Depth 1. Evaluate threat models 2. Encrypt in transit 3.

    Encrypt at rest 4. Limit access to keys 5. GOTO 1
  23. 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?