# DIDComm spec assumptions

## JOSE assumptions for DIDComm lib v0.1

### JSON Serialization Syntax

* JWE - General Serialization only
* JWS
- General for JWS Signed DIDComm Messaged
- Flattened for jws attachment

### ECDH-1PU

* `apu` is same as in [DIDComm Spec](https://identity.foundation/didcomm-messaging/spec/#ecdh-1pu-key-wrapping-and-common-protected-headers)
* `apv` is same as in [DIDComm Spec](https://identity.foundation/didcomm-messaging/spec/#ecdh-1pu-key-wrapping-and-common-protected-headers)
* `skid` is same as in [DIDComm Spec](https://identity.foundation/didcomm-messaging/spec/#ecdh-1pu-key-wrapping-and-common-protected-headers)
* only one sender key:
* one value in `skid`/`apu`
* one `epk` value in `protected` header for all recipients

### ECDH-ES

* Only one `epk` in `protected` header for all recipients
* `apv` in `protected` header
* `apv` is same as in `ECDH-1PU`
* `apu` is empty (must not present in `protected` header at all)

### Common

* `kid` MUST be presented in JWE Per-Recipient Unprotected Header
* `kid` MUST be presented in JWS Per-Signature Unprotected Header
* `aad` is `base64Url(protected_header)`
* Only one and the same `alg` in `protected` header for all recipients
* `skid` and `kid` are UTF8 string

## Forward

* [alternative endpoint](https://identity.foundation/didcomm-messaging/spec/#alternative-endpoints):
* how it works actually:
* we have mediator's `MEDIATOR_DID` in `serviceEndpoint` in a recipient's DID Doc Service (`DIDCommMessaging`)
* we resolve mediator's DID Doc (so we know its `keyAgreement` keys for anoncrypt)
* we put **its DID** (the original one from recipient's `serviceEndpoint`) **at the beginning** of `routingKeys` so the mediator would be the first who receives the message and the last (top, outermost) in the forward envelops onion
* *divergences with the spec*:
* we don't put all `keyAgreement` into `routingKeys`
* we put at the beginning (not at end)
* then we can start just usual [forward wrapping process](https://identity.foundation/didcomm-messaging/spec/#sender-forward-process)