[#AEADChaCha20Poly1305-Keystream]
= xref:AEADChaCha20Poly1305.adoc[AEADChaCha20Poly1305]::Keystream
:relfileprefix: ../
:mrdocs:

Get a number of keystream bytes from the underlying stream cipher.

== Synopsis

Declared in `<crypto/chacha20poly1305.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
Keystream(
    xref:AEADChaCha20Poly1305/Nonce96.adoc[Nonce96] nonce,
    std::span<std::byte> keystream) noexcept;
----

== Description

This is equivalent to Encrypt() with plain set to that many zero bytes, and dropping the last EXPANSION bytes off the result.

== Return Value

a number of keystream bytes from the underlying stream cipher.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *nonce*
| The 96‐bit nonce.
| *keystream*
| Output buffer receiving the keystream bytes.
|===


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