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.\"
.IX Title "RSA_check_key 3"
.TH RSA_check_key 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
RSA_check_key \- validate private RSA keys
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& int RSA_check_key(RSA *rsa);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This function validates \s-1RSA\s0 keys. It checks that \fBp\fR and \fBq\fR are
in fact prime, and that \fBn = p*q\fR.
.PP
It also checks that \fBd*e = 1 mod (p\-1*q\-1)\fR,
and that \fBdmp1\fR, \fBdmq1\fR and \fBiqmp\fR are set correctly or are \fB\s-1NULL\s0\fR.
.PP
As such, this function can not be used with any arbitrary \s-1RSA\s0 key object,
even if it is otherwise fit for regular \s-1RSA\s0 operation. See \fB\s-1NOTES\s0\fR for more
information.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fIRSA_check_key()\fR returns 1 if \fBrsa\fR is a valid \s-1RSA\s0 key, and 0 otherwise.
\&\-1 is returned if an error occurs while checking the key.
.PP
If the key is invalid or an error occurred, the reason code can be
obtained using \fIERR_get_error\fR\|(3).
.SH "NOTES"
.IX Header "NOTES"
This function does not work on \s-1RSA\s0 public keys that have only the modulus
and public exponent elements populated. It performs integrity checks on all
the \s-1RSA\s0 key material, so the \s-1RSA\s0 key structure must contain all the private
key data too.
.PP
Unlike most other \s-1RSA\s0 functions, this function does \fBnot\fR work
transparently with any underlying \s-1ENGINE\s0 implementation because it uses the
key data in the \s-1RSA\s0 structure directly. An \s-1ENGINE\s0 implementation can
override the way key data is stored and handled, and can even provide
support for \s-1HSM\s0 keys \- in which case the \s-1RSA\s0 structure may contain \fBno\fR
key data at all! If the \s-1ENGINE\s0 in question is only being used for
acceleration or analysis purposes, then in all likelihood the \s-1RSA\s0 key data
is complete and untouched, but this can't be assumed in the general case.
.SH "BUGS"
.IX Header "BUGS"
A method of verifying the \s-1RSA\s0 key using opaque \s-1RSA API\s0 functions might need
to be considered. Right now \fIRSA_check_key()\fR simply uses the \s-1RSA\s0 structure
elements directly, bypassing the \s-1RSA_METHOD\s0 table altogether (and
completely violating encapsulation and object-orientation in the process).
The best fix will probably be to introduce a \*(L"\fIcheck_key()\fR\*(R" handler to the
\&\s-1RSA_METHOD\s0 function table so that alternative implementations can also
provide their own verifiers.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIrsa\fR\|(3), \fIERR_get_error\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIRSA_check_key()\fR appeared in OpenSSL 0.9.4.