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.IX Title "BN_mod_inverse 3"
.TH BN_mod_inverse 3 "2003-07-24" "0.9.7g" "OpenSSL"
.SH "NAME"
BN_mod_inverse \- compute inverse modulo n
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/bn.h>
.Ve
.PP
.Vb 2
\& BIGNUM *BN_mod_inverse(BIGNUM *r, BIGNUM *a, const BIGNUM *n,
\&           BN_CTX *ctx);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIBN_mod_inverse()\fR computes the inverse of \fBa\fR modulo \fBn\fR
places the result in \fBr\fR (\f(CW\*(C`(a*r)%n==1\*(C'\fR). If \fBr\fR is \s-1NULL\s0,
a new \fB\s-1BIGNUM\s0\fR is created.
.PP
\&\fBctx\fR is a previously allocated \fB\s-1BN_CTX\s0\fR used for temporary
variables. \fBr\fR may be the same \fB\s-1BIGNUM\s0\fR as \fBa\fR or \fBn\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIBN_mod_inverse()\fR returns the \fB\s-1BIGNUM\s0\fR containing the inverse, and
\&\s-1NULL\s0 on error. The error codes can be obtained by \fIERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIbn\fR\|(3), \fIERR_get_error\fR\|(3), \fIBN_add\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIBN_mod_inverse()\fR is available in all versions of SSLeay and OpenSSL.