---
title: "expand(pseudoRandomKey:info:into:)"
framework: cryptokit
role: symbol
role_heading: Type Method
platforms: [iOS 27.0+, iPadOS 27.0+, Mac Catalyst 27.0+, macOS 27.0+, tvOS 27.0+, visionOS 27.0+, watchOS 27.0+]
path: "cryptokit/hkdf/expand(pseudorandomkey:info:into:)"
---

# expand(pseudoRandomKey:info:into:)

Expands cryptographically strong key material into a derived symmetric key.

## Declaration

```swift
static func expand(pseudoRandomKey prk: RawSpan, info: RawSpan?, into output: inout OutputRawSpan)
```

## Parameters

- `prk`: A pseudorandom, cryptographically strong key generated from the extract(inputKeyMaterial:salt:) function.
- `info`: The shared information to use for key derivation.

## Discussion

Discussion Generate cryptographically strong key material to use with this function by calling extract(inputKeyMaterial:salt:).