[#EVP_DecryptInit_ex]
= EVP_DecryptInit_ex
:mrdocs:

Initialize `ctx` for decryption with an optional ENGINE implementation.

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP_DecryptInit_ex(
    xref:EVP_CIPHER_CTX.adoc[EVP_CIPHER_CTX]* ctx,
    xref:EVP_CIPHER-07.adoc[EVP_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.

== Parameters

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


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