[#EVP_BytesToKey]
= EVP_BytesToKey
:mrdocs:

Derive a cipher key and IV from a password using the legacy EVP_BytesToKey KDF.

== Synopsis

Declared in `<openssl/evp.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
EVP_BytesToKey(
    xref:EVP_CIPHER-07.adoc[EVP_CIPHER] const* type,
    xref:EVP_MD.adoc[EVP_MD] const* md,
    unsigned char const* salt,
    unsigned char const* data,
    int datal,
    int count,
    unsigned char* key,
    unsigned char* iv);
----

== Return Value

Length of the derived key in bytes, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *type*
| Cipher whose key and IV lengths determine the output sizes.
| *md*
| Digest used in the iterative key derivation (commonly EVP_md5()).
| *salt*
| Optional 8‐byte salt, or NULL.
| *data*
| Password / passphrase bytes.
| *datal*
| Length of `data` in bytes.
| *count*
| Iteration count (higher slows brute‐force attacks).
| *key*
| Output buffer for the derived key, or NULL to skip.
| *iv*
| Output buffer for the derived IV, or NULL to skip.
|===


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