[#EVP_PKEY_derive]
= EVP_PKEY_derive
:mrdocs:

Derive a shared secret using a context initialized with EVP_PKEY_derive_init().

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP_PKEY_derive(
    xref:EVP_PKEY_CTX.adoc[EVP_PKEY_CTX]* ctx,
    unsigned char* key,
    size_t* keylen);
----

== Return Value

1 on success, or 0 / a negative value on failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| Key derivation context that already has a peer key configured when required.
| *key*
| Output buffer for the shared secret, or NULL to query the required length.
| *keylen*
| On input, size of `key;` on output, number of bytes written or required.
|===


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