RSA_CHECK_KEY(3) | Library Functions Manual | RSA_CHECK_KEY(3)

# NAME

`RSA_check_key` — validate private RSA keys

# SYNOPSIS

library “libcrypto”
`#include <openssl/rsa.h>`

int
`RSA_check_key`(RSA *rsa);

# DESCRIPTION

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

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

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. Therefore, it cannot be used with any arbitrary RSA key object, even if it is otherwise fit for regular RSA operation.

# RETURN VALUES

`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).

# SEE ALSO

BN_is_prime_ex(3), RSA_get0_key(3), RSA_new(3)

# HISTORY

`RSA_check_key`() first appeared in OpenSSL 0.9.4 and has been available since OpenBSD 2.6.

# 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 `check_key`() handler to the RSA_METHOD function table so that alternative implementations can also provide their own verifiers.

June 8, 2025 | Debian