[#FSChaCha20Poly1305-Decrypt-05]
= xref:FSChaCha20Poly1305.adoc[FSChaCha20Poly1305]::Decrypt
:relfileprefix: ../
:mrdocs:

Decrypt a message with a specified aad. Returns true if valid.

== Synopsis

Declared in `<crypto/chacha20poly1305.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
bool
Decrypt(
    std::span<std::byte const> cipher,
    std::span<std::byte const> aad,
    std::span<std::byte> plain) noexcept;
----

== Description

Requires cipher.size() = plain.size() + EXPANSION.

== Return Value

true if the tag is valid and decryption succeeded, false otherwise.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *cipher*
| The ciphertext and authentication tag to decrypt and verify.
| *aad*
| The associated data to authenticate.
| *plain*
| Output buffer receiving the recovered plaintext.
|===


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