---
title: SecTransformDataBlock
framework: security
role: symbol
role_heading: Type Alias
path: security/sectransformdatablock
---

# SecTransformDataBlock

A block used to override the default data handling for a transform.

## Declaration

```swift
typealias SecTransformDataBlock = (CFTypeRef) -> Unmanaged<CFTypeRef>?
```

## Parameters

- `data`: The data to be processed. When this block is used to to implement the doc://com.apple.security/documentation/Security/kSecTransformActionProcessData action, the data is the input data that is to be processed into the output data. When this block is used to implement the doc://com.apple.security/documentation/Security/kSecTransformActionInternalizeExtraData action, the data is a doc://com.apple.documentation/documentation/CoreFoundation/CFDictionary that contains the data that needs to be imported.

## Return Value

Return Value NULL for the kSecTransformActionInternalizeExtraData action, the data to be passed to the output attribute for any other action, or a CFError instance on failure.