Server-Side Encryption of Objects

MinIO Server-Side Encryption (SSE) protects objects as part of write operations, allowing clients to take advantage of server processing power to secure objects at the storage layer (encryption-at-rest). SSE also provides key functionality to regulatory and compliance requirements around secure locking and erasure.

MinIO SSE uses the MinIO Key Encryption Service (KES) and an external Key Management Service (KMS) for performing secured cryptographic operations at scale. MinIO also supports client-managed key management, where the application takes full responsibility for creating and managing encryption keys for use with MinIO SSE.

MinIO SSE is feature and API compatible with AWS Server-Side Encryption and supports the following encryption strategies:

MinIO SSE requires enabling Network Encryption (TLS).

Secure Erasure and Locking

MinIO requires access to the Encryption Key (EK) and external Key Management System (KMS) used as part of SSE operations to decrypt an object. You can use this dependency to securely erase and lock objects from access by disabling access to the EK or KMS used for encryption.

General strategies include, but are not limited to:

• Seal the KMS such that it cannot be accessed by MinIO server anymore. This locks all SSE-KMS or SSE-S3 encrypted objects protected by any EK stored on the KMS. The encrypted objects remain unreadable as long as the KMS remains sealed.

• Seal/Unmount an EK. This locks all SSE-KMS or SSE-S3 encrypted objects protected by that EK. The encrypted objects remain unreadable as long as the CMK(s) remains sealed.

• Delete an EK. This renders all SSE-KMS or SSE-S3 encrypted objects protected by that EK as permanently unreadable. The combination of deleting an EK and deleting the data may fulfill regulatory requirements around secure deletion of data.

  Deleting an EK is typically irreversible. Exercise extreme caution before intentionally deleting a master key.

For more information, see:

• SSE-KMS Secure Erasure and Locking
• SSE-S3 Secure Erasure and Locking
• SSE-C Secure Erasure and Locking

Cryptographic Construction

The following facts describe the construction shared by the SSE schemes. They are audit-level reference material: not necessary for configuring or using SSE, but useful when reviewing what is actually stored and in what form. The description originates from the encryption design notes inherited from upstream MinIO and retained by Silo.

• Object content is en/decrypted with an authenticated encryption scheme (AEAD) organized as a Secure Channel: the plaintext is split into fixed-size chunks, and each chunk is sealed separately with a unique key-nonce combination. The last chunk may be smaller and is treated specially to prevent truncation attacks.
• For multi-part objects, each part is sealed with its own key derived from the Object Encryption Key (OEK) and the part number through a PRF — so the OEK itself is never used directly as a part key.
• The PRF is HMAC-SHA-256. The pinned sio implementation prefers AES-256-GCM when hardware acceleration is available (including supported x86 and ARM64 CPUs), and ChaCha20-Poly1305 otherwise.
• Object encryption keys are 256 bits. The content-encryption format uses 96-bit nonces; the separate key-sealing metadata carries a 256-bit IV. These are different fields and must not be confused.
• The chunk size is 65536 bytes, which bounds a single encrypted object or part at 65536 * 2^32 = 256 TiB of plaintext at the cryptographic-format level. This is not the supported S3 object or multipart-part size limit.
• Object-key derivation and key-sealing IV generation use crypto/rand; sio also defaults to that cryptographically secure random source. Neither keys nor nonces should be replaced with merely unique counters.