POST /api/crypto/cipher

Select the cipher for this session.

Asks the key server to select a cipher for the calling session.

cipher is REQUIRED and must be a non-empty string, and both halves of that are refused rather than defaulted: a falsy cipher is not a default, because the binding then omits the parameter entirely and sends a different request rather than a defaulted one.

The value is matched case-insensitively against the key server's own allowed-algorithm list, and the matched spelling is what goes on the wire.

WARNING: accepted: true is not confirmation. verified is always false on this route, deliberately. The only operation that reports a session's cipher is one this Gateway's administrative identity is measured to be refused, so there is nothing to read back with. The response says the key server did not refuse.

3DES, DES, RC2 and RC4 are refused here regardless of what the key server configuration lists. The binding still carries a 3DES constant; its presence there is not permission to use it.

Authentication

Send the session id as Authorization: Bearer <session id>, and an RFC 9449 DPoP proof in the DPoP header if your session is bound to a key. The two are required together, not as alternatives — see Authenticating and Proving you hold your key.

This surface sets no cookie

There is no session cookie on any response and none is read on any request. Do not set credentials: "include" on a browser fetch.

Request

Field	Type	Required	Description
cipher	string	yes

Example

{
  "cipher": "..."
}

Responses

200

The key server accepted the selection. It has not been read back.

Field	Type	Required	Description
requested	string	yes
sent	string	yes	The spelling actually sent
allowedAlgorithms	array of string	yes
accepted	true (constant)	yes
verified	false (constant)	yes
detail	string	yes

Example

{
  "requested": "...",
  "sent": "...",
  "allowedAlgorithms": [
    "..."
  ],
  "accepted": true,
  "verified": false,
  "detail": "..."
}

400

BAD_REQUEST -- cipher absent, not a string, empty, prohibited by this product's crypto posture, or not in this key server's allowed list (which the detail enumerates, including the case where it lists none).

401

No live session, or a DPoP proof that did not verify.

SESSION_NOT_FOUND -- the credential names no session this Gateway holds. SESSION_EXPIRED -- it aged out. Both carry reauth: true; obtain a new credential rather than retrying.

PROOF_* -- the sender constraint refused. See the DPoP section of this document for the full table; PROOF_MALFORMED is a 400 and PROOF_REPLAY_CACHE_FULL a 503, and the rest are here.

SCOPED_CREDENTIAL_EXPIRED -- a scoped browser credential passed its fixed lifetime. Use does not extend it: an idle timeout would be refreshed by exactly the traffic a stolen handle produces.

403

Authenticated, and refused. The codes differ in what they say about where the refusal came from: ACCESS_DENIED and PRINCIPAL_DISABLED are the key server's, while NOT_WRITABLE, BUILT_IN_PRINCIPAL, OWN_ACCOUNT and OBJECT_NOT_IN_CREDENTIAL_SCOPE are decided by the Gateway before anything is sent.

500

A fault rather than a refusal.

OP_FAILED is the catch-all: the key server refused in words that match no classified pattern, so the Gateway cannot say more than that the operation did not happen. Some key server refusals that are conceptually a caller error arrive here rather than as a 4xx, because the wire carries no distinguishing code -- where a route can recognise one from its message it maps it, and each such mapping is documented on the operation.

503

A capacity ceiling or a missing deployment prerequisite. retryable says which.

A scope of session or process names the ceiling that was hit, and the response carries Retry-After.

Error handling

Every failure answers JSON carrying at least code and detail. Match on code — detail is written for a human debugging the call and its wording is not part of the contract. See the error model.

Status	Meaning
400	BAD_REQUEST -- cipher absent, not a string, empty, prohibited by this product's crypto posture, or not in this key server's allowed list (which the detail enumerates, including the case where it lists none).
401	No live session, or a DPoP proof that did not verify. SESSION_NOT_FOUND -- the credential names no session this Gateway holds. SESSION_EXPIRED -- it aged out. Both carry reauth: true; obtain a new credential rather than retrying. PROOF_* -- the sender constraint refused. See the DPoP section of this document for the full table; PROOF_MALFORMED is a 400 and PROOF_REPLAY_CACHE_FULL a 503, and the rest are here. SCOPED_CREDENTIAL_EXPIRED -- a scoped browser credential passed its fixed lifetime. Use does not extend it: an idle timeout would be refreshed by exactly the traffic a stolen handle produces.
403	Authenticated, and refused. The codes differ in what they say about where the refusal came from: ACCESS_DENIED and PRINCIPAL_DISABLED are the key server's, while NOT_WRITABLE, BUILT_IN_PRINCIPAL, OWN_ACCOUNT and OBJECT_NOT_IN_CREDENTIAL_SCOPE are decided by the Gateway before anything is sent.
500	A fault rather than a refusal. OP_FAILED is the catch-all: the key server refused in words that match no classified pattern, so the Gateway cannot say more than that the operation did not happen. Some key server refusals that are conceptually a caller error arrive here rather than as a 4xx, because the wire carries no distinguishing code -- where a route can recognise one from its message it maps it, and each such mapping is documented on the operation.
503	A capacity ceiling or a missing deployment prerequisite. retryable says which. A scope of session or process names the ceiling that was hit, and the response carries Retry-After.