[#BN_mod_inverse]
= BN_mod_inverse
:mrdocs:

Compute the modular inverse of `a` modulo `n.`

== Synopsis

Declared in `<openssl/bn.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:BIGNUM.adoc[BIGNUM]*
BN_mod_inverse(
    xref:BIGNUM.adoc[BIGNUM]* ret,
    xref:BIGNUM.adoc[BIGNUM] const* a,
    xref:BIGNUM.adoc[BIGNUM] const* n,
    xref:BN_CTX.adoc[BN_CTX]* ctx);
----

== Return Value

Result BIGNUM (possibly newly allocated) on success, or NULL if no inverse exists / on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ret*
| Existing BIGNUM to receive the result, or NULL to allocate.
| *a*
| Value to invert.
| *n*
| Modulus; must be non‐zero.
| *ctx*
| BN_CTX scratch space.
|===


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