.\"	$OpenBSD: RSA_generate_key.3,v 1.13 2019/06/10 14:58:48 schwarze Exp $
.\"	OpenSSL RSA_generate_key.pod bb6c5e7f Feb 5 10:29:22 2017 -0500
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.Dd $Mdocdate: June 10 2019 $
.Dt RSA_GENERATE_KEY 3
.Os
.Sh NAME
.Nm RSA_generate_key_ex ,
.Nm RSA_generate_key
.Nd generate RSA key pair
.Sh SYNOPSIS
.In openssl/rsa.h
.Ft int
.Fo RSA_generate_key_ex
.Fa "RSA *rsa"
.Fa "int bits"
.Fa "BIGNUM *e"
.Fa "BN_GENCB *cb"
.Fc
.Pp
Deprecated:
.Pp
.Ft RSA *
.Fo RSA_generate_key
.Fa "int num"
.Fa "unsigned long e"
.Fa "void (*callback)(int, int, void *)"
.Fa "void *cb_arg"
.Fc
.Sh DESCRIPTION
.Fn RSA_generate_key_ex
generates a key pair and stores it in
.Fa rsa .
.Pp
The modulus size will be of length
.Fa bits ,
and the public exponent will be
.Fa e .
Key sizes with
.Fa num
< 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
.Fa cb
is not
.Dv NULL ,
it will be called as follows using the
.Xr BN_GENCB_call 3
function:
.Bl -bullet
.It
While a random prime number is generated, it is called as described in
.Xr BN_generate_prime 3 .
.It
When the
.Fa n Ns -th
randomly generated prime is rejected as not suitable for
the key,
.Fn BN_GENCB_call cb 2 n
is called.
.It
When a random p has been found with p-1 relatively prime to
.Fa e ,
it is called as
.Fn BN_GENCB_call cb 3 0 .
.El
.Pp
The process is then repeated for prime q with
.Fn BN_GENCB_call cb 3 1 .
.Pp
.Fn RSA_generate_key
is deprecated.
New applications should use
.Fn RSA_generate_key_ex
instead.
.Fn RSA_generate_key
works in the same way as
.Fn RSA_generate_key_ex
except it uses "old style" call backs.
See
.Xr BN_generate_prime 3
for further details.
.Sh RETURN VALUES
.Fn RSA_generate_key_ex
returns 1 on success or 0 on error.
.Fn RSA_generate_key
returns the key on success or
.Dv NULL
on error.
.Pp
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr BN_generate_prime 3 ,
.Xr RSA_get0_key 3 ,
.Xr RSA_meth_set_keygen 3 ,
.Xr RSA_new 3
.Sh HISTORY
.Fn RSA_generate_key
appeared in SSLeay 0.4 or earlier and had its
.Fa cb_arg
argument added in SSLeay 0.9.0.
It has been available since
.Ox 2.4 .
.Pp
.Fn RSA_generate_key_ex
first appeared in OpenSSL 0.9.8 and has been available since
.Ox 4.5 .
.Sh BUGS
.Fn BN_GENCB_call cb 2 x
is used with two different meanings.
.Pp
.Fn RSA_generate_key
goes into an infinite loop for illegal input values.