## NAME

RSA_check_key — validate private RSA keys

## Synopsis

`#include <openssl/rsa.h>`

int
RSA_check_key(RSA *rsa);

## DESCRIPTION

This function validates RSA keys. It checks that *p* and *q* are
in fact prime, and that *n = p*q*.

It also checks that *d*e = 1 mod (p-1*q-1)*,
and that *dmp1*, *dmq1* and *iqmp* are
set correctly or are *NULL*.

As such, this function can not be used with any arbitrary
RSA key object, even if it is otherwise fit for regular RSA operation.
See *NOTES* for more information.

## RETURN VALUE

RSA_check_key() returns 1 if *rsa* is a
valid RSA key, and 0 otherwise. -1 is returned if an error occurs
while checking the key.

If the key is invalid or an error occurred, the reason code
can be obtained using *ERR_get_error*(3).

## NOTES

This function does not work on RSA public keys that have only
the modulus and public exponent elements populated. It performs
integrity checks on all the RSA key material, so the RSA key structure
must contain all the private key data too.

Unlike most other RSA functions, this function does *not* work
transparently with any underlying ENGINE implementation because
it uses the key data in the RSA structure directly. An ENGINE implementation
can override the way key data is stored and handled, and can even
provide support for HSM keys - in which case the RSA structure may
contain *no* key data at all! If the ENGINE in
question is only being used for acceleration or analysis purposes,
then in all likelihood the RSA key data is complete and untouched,
but this can't be assumed in the general case.

## Restrictions

A method of verifying the RSA key using opaque RSA API functions
might need to be considered. Right now RSA_check_key() simply uses
the RSA structure elements directly, bypassing the RSA_METHOD table altogether
(and completely violating encapsulation and object-orientation in
the process). The best fix will probably be to introduce a "check_key()"
handler to the RSA_METHOD function table so that alternative implementations
can also provide their own verifiers.

## SEE ALSO

*rsa*(3), *ERR_get_error*(3)

## HISTORY

RSA_check_key() appeared in OpenSSL 0.9.4.