# RSA_check_key(3)

**RSA_check_key(3)** OpenSSL **RSA_check_key(3)**

## 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.

## BUGS

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
1.0.2t Last change: 2019-09-10 1
**RSA_check_key(3)** OpenSSL **RSA_check_key(3)**
"*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.
1.0.2t Last change: 2019-09-10 2

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