[#EVP_DecryptInit_ex]
= EVP&lowbar;DecryptInit&lowbar;ex
:mrdocs:

Initialize `ctx` for decryption with an optional ENGINE implementation&period;

== Synopsis

Declared in `&lt;openssl&sol;evp&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP&lowbar;DecryptInit&lowbar;ex(
    xref:EVP_CIPHER_CTX.adoc[EVP&lowbar;CIPHER&lowbar;CTX]* ctx,
    xref:EVP_CIPHER-07.adoc[EVP&lowbar;CIPHER] const* cipher,
    xref:ENGINE.adoc[ENGINE]* impl,
    unsigned char const* key,
    unsigned char const* iv);
----

== Return Value

1 on success, or 0 on failure&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| Cipher context to initialize&period;
| *cipher*
| Cipher algorithm, or NULL to reuse the current algorithm&period;
| *impl*
| Optional ENGINE providing the implementation, or NULL&period;
| *key*
| Decryption key bytes, or NULL to set later&period;
| *iv*
| Initialization vector, or NULL when not required &sol; set later&period;
|===


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