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.\" ========================================================================
.\"
.IX Title "RSA_generate_key 3"
.TH RSA_generate_key 3 "2002-09-25" "1.1.0-dev" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
RSA_generate_key \- generate RSA key pair
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& RSA *RSA_generate_key(int num, unsigned long e,
\&    void (*callback)(int,int,void *), void *cb_arg);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIRSA_generate_key()\fR generates a key pair and returns it in a newly
allocated \fB\s-1RSA\s0\fR structure. The pseudo-random number generator must
be seeded prior to calling \fIRSA_generate_key()\fR.
.PP
The modulus size will be \fBnum\fR bits, and the public exponent will be
\&\fBe\fR. Key sizes with \fBnum\fR < 1024 should be considered insecure.
The exponent is an odd number, typically 3, 17 or 65537.
.PP
A callback function may be used to provide feedback about the
progress of the key generation. If \fBcallback\fR is not \fB\s-1NULL\s0\fR, it
will be called as follows:
.IP "\(bu" 4
While a random prime number is generated, it is called as
described in \fIBN_generate_prime\fR\|(3).
.IP "\(bu" 4
When the n\-th randomly generated prime is rejected as not
suitable for the key, \fBcallback(2, n, cb_arg)\fR is called.
.IP "\(bu" 4
When a random p has been found with p\-1 relatively prime to \fBe\fR,
it is called as \fBcallback(3, 0, cb_arg)\fR.
.PP
The process is then repeated for prime q with \fBcallback(3, 1, cb_arg)\fR.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
If key generation fails, \fIRSA_generate_key()\fR returns \fB\s-1NULL\s0\fR; the
error codes can be obtained by \fIERR_get_error\fR\|(3).
.SH "BUGS"
.IX Header "BUGS"
\&\fBcallback(2, x, cb_arg)\fR is used with two different meanings.
.PP
\&\fIRSA_generate_key()\fR goes into an infinite loop for illegal input values.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIERR_get_error\fR\|(3), \fIopenssl_rand\fR\|(3), \fIopenssl_rsa\fR\|(3),
\&\fIRSA_free\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
The \fBcb_arg\fR argument was added in SSLeay 0.9.0.