[#BN_mod_exp]
= BN_mod_exp
:mrdocs:

Compute modular exponentiation: `r` = (`a` ˆ `p)` mod `m.`

== Synopsis

Declared in `<openssl/bn.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
BN_mod_exp(
    xref:BIGNUM.adoc[BIGNUM]* r,
    xref:BIGNUM.adoc[BIGNUM] const* a,
    xref:BIGNUM.adoc[BIGNUM] const* p,
    xref:BIGNUM.adoc[BIGNUM] const* m,
    xref:BN_CTX.adoc[BN_CTX]* ctx);
----

== Return Value

1 on success, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *r*
| Destination for the result.
| *a*
| Base.
| *p*
| Exponent.
| *m*
| Modulus; must be non‐zero.
| *ctx*
| BN_CTX for temporary storage.
|===


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