[#EVP_PKEY_decapsulate]
= EVP_PKEY_decapsulate
:mrdocs:

Decapsulate a shared secret from a KEM ciphertext using a context from EVP_PKEY_decapsulate_init().

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP_PKEY_decapsulate(
    xref:EVP_PKEY_CTX.adoc[EVP_PKEY_CTX]* ctx,
    unsigned char* unwrapped,
    size_t* unwrappedlen,
    unsigned char const* wrapped,
    size_t wrappedlen);
----

== Return Value

1 on success, or a non‐positive value on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| Decapsulation context holding the private key.
| *unwrapped*
| Buffer for the recovered shared secret, or NULL to query size via `unwrappedlen.`
| *unwrappedlen*
| On entry, capacity of `unwrapped` when non‐NULL; on return, bytes written or required.
| *wrapped*
| Encapsulation ciphertext bytes.
| *wrappedlen*
| Length of `wrapped` in bytes.
|===


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