Understanding Key Manager cryptography
Cryptographic primitives in Scaleway Key Manager
This page provides information on the core cryptographic mechanisms used by Key Manager. It explains how cryptographic keys are generated, managed, and used to encrypt data. Key Manager uses these mechanisms in compliance with the cryptographic guidelines issued by France's national cybersecurity agency, as outlined in the ANSSI-PA-079 recommendations, to ensure the confidentiality and integrity of customer data.
Random number generation
Key encryption key (KEK) generation
Scaleway Key Manager uses a Cryptographically Secure Pseudorandom Number Generator (CSPRNG) to generate both keying material for managed keys and cryptographically unique initialization vectors (IVs).
This CSPRNG is based on the ChaCha-based pseudorandom number generator provided by modern Linux kernels. It is seeded with high-entropy, unpredictable sources, such as:
- Timing variations from hardware events
- True Random Number Generators (TRNGs), including the
RDSEEDandRDRANDinstructions available on AMD64 processors
Customer-provided KEKs (BYOK)
Scaleway Key Manager supports Bring Your Own Key (BYOK), allowing customers to import their own key material. In this model, Scaleway does not generate keys on behalf of the customer. Instead, the responsibility for generating strong key material lies with the user.
To protect against direct reuse, imported key material is not used directly. Instead, it is processed using the HKDF algorithm (HMAC-based Key Derivation Function) with SHA-256 as the hash algorithm, incorporating secure random bytes added as a salt value.
Symmetric encryption
Scaleway Key Manager uses AES-256-GCM (AES with a 256-bit key in Galois/Counter Mode) with authenticated associated data (AEAD) for encrypting and decrypting user payloads.
To reduce the risk of key overuse, plaintext payloads are limited to a maximum size of 64 KiB. A unique 96-bit initialization vector (IV) is generated using the CSPRNG described in the section above.