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Key Management Service
Key types

KMS key types

Each KMS key has a fixed key type set at creation. The key type determines which operations are supported. Choose the type based on your use case before you create the key; key types cannot be changed after creation.

Supported key types

Key typeEncrypt / decryptSign / verifyHMACPublic key exportBYOK import
aes128-gcm96✓———✓
aes256-gcm96 (default)✓———✓
chacha20-poly1305✓———✓
rsa-2048✓✓—✓✓
rsa-3072✓✓—✓✓
rsa-4096✓✓—✓✓
ecdsa-p256—✓—✓✓
ecdsa-p384—✓—✓✓
ecdsa-p521—✓—✓✓
ed25519—✓—✓✓
hmac——✓—✗
hmac-sha256——✓—✗
hmac-sha512——✓—✗

Use case guidance

Volume and secrets encryption

Use symmetric key types for encrypting data at rest, secrets, and envelope encryption workflows:

  • aes256-gcm96 — Recommended default for most encryption use cases
  • aes128-gcm96 — Lower key size when policy allows
  • chacha20-poly1305 — Alternative symmetric cipher

Symmetric keys support convergent encryption: the same plaintext and encryption context can produce the same ciphertext. This can be useful for deduplication but requires careful context design.

DNSSEC and document signing

Use asymmetric signing key types:

  • ecdsa-p256 — Recommended for DNSSEC; Thalassa DNS auto-provisions this type when you enable DNSSEC without specifying a key
  • ecdsa-p384 / ecdsa-p521 — Higher-strength ECDSA curves
  • rsa-2048 / rsa-3072 / rsa-4096 — RSA signing where required by policy or integrations
  • ed25519 — Compact signatures for application attestation and modern signing workflows

Message authentication

Use HMAC key types when you need to generate or verify message authentication codes:

  • hmac — Default HMAC algorithm
  • hmac-sha256 / hmac-sha512 — Explicit hash functions

HMAC keys cannot be imported via BYOK.

Small-payload RSA encryption

RSA key types support direct encrypt and decrypt for small payloads only. RSA-2048 has an effective plaintext limit of approximately 190 bytes. For bulk data, use symmetric keys with envelope encryption instead.

Public key workflows

RSA, ECDSA, and Ed25519 keys support public key export via GET …/public-key. Use exported public keys for offline signature verification or client-side RSA encryption. Public key export does not require the exportAllowed flag.

Choosing a default

ScenarioRecommended key type
Application secrets and envelope encryptionaes256-gcm96
DNS zone signingecdsa-p256
API request signing / webhookshmac-sha256 or ed25519
Code signing with RSA requirementrsa-3072 or rsa-4096
Regulatory BYOK symmetric keyMatch your source material (typically aes256-gcm96)

See Creating keys to create a key with your chosen type, and Sign, verify, and HMAC for operation details per type.

Getting startedCreating keys