# ALG_ECDH_ES_A256KW

> `const` **ALG\_ECDH\_ES\_A256KW**: `-31` = `-31`

Defined in: [packages/filecoin-encryption-envelope/src/cose/constants.ts:88](https://github.com/FilOzone/synapse-sdk/blob/9ad84d812e1dd635b76420a7d9388555a04f31b6/packages/filecoin-encryption-envelope/src/cose/constants.ts#L88)

ECDH-ES + AES key wrap. Deferred — defined here so recipients using it can
be recognised and skipped, not unwrapped.

When that profile is written, the reference is RFC 9053 **§6.4** (key
agreement *with* key wrap), not §6.3 (direct key agreement).