> ## Documentation Index
> Fetch the complete documentation index at: https://docs.deribit.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Security Definition Request(c) (Production FIX API)

> SecurityDefinitionRequest(c) requests detailed contract definitions for one instrument on the Deribit production FIX API before market data subscription.

Request a specific Security to be traded with the second party. The requested
security is defined as a multileg security made up of two or more instrument
legs. Also it can be used to query a list of combo-instrument securities offered
by trading parties. (This method is the FIX equivalent of `private/create_combo`,
`public/get_combo_ids` and `private/get_combo_details` request for WS/HTTPS
end-points depending on `SecurityRequestType (321)` tag value).

### Arguments

| Tag | Name | Type | Required | Comments |
| - | - | - | - | - |
| 320 | `SecurityReqID` | String | Yes | Request identifier |
| 321 | `SecurityRequestType` | int | Yes | Type of `Security Definition Request`(`c`).<p>Valid values: <ul><li>`0` = Request Security details, specifications by `SecurityId`,</li><li>`1` = Request Security identity for the specifications provided, the combo-instrument will be created if necessary. </li><li>`3` = Request list of existing combo-instruments</li></ul></p> |
| 15 | `Currency` | String | Yes | Required if `SecurityRequestType` = `3`, examples: `BTC`, `ETH` |
| 48 | `SecurityID` | String | No | Required if `SecurityRequestType` = `0`. Identifies combo instrument. |
| | Group `InstrmtLegGrp` | | | |
| 555 | `NoLegs` | int | Yes | Number of legs that make up the Security |
| =>600 | `LegSymbol` | String | No | Non-combo instrument name |
| =>624 | `LegSide` | char | No | Valid values:<ul> <li>`1` = Buy,</li> <li>`2` = Sell</li></ul> |
| =>623 | `LegRatioQty` | int | No | Positive integer for the strategy |

### Response

The server sends the [`Security Definition (d)`](/fix-api/production/security-definition) message as
a response, or rejects the request.


## Related topics

- [Security Definition(d) (Production FIX API)](/fix-api/production/security-definition.md)
- [Security List Request(x) (Production FIX API)](/fix-api/production/security-list-request.md)
- [Security Status Request(e) (Production FIX API)](/fix-api/production/security-status-request.md)
- [Security List(y) (Production FIX API)](/fix-api/production/security-list.md)
- [Security Status(f) (Production FIX API)](/fix-api/production/security-status.md)