RSA_check_key_ex, RSA_check_key - validate private RSA keys
int RSA_check_key_ex(RSA *rsa, BN_GENCB *cb);
int RSA_check_key(RSA *rsa);
RSA_check_key_ex() function validates RSA keys. It checks that p
and q are in fact prime, and that n = p*q.
It does not work on RSA public keys that have only the modulus and
public exponent elements populated. It also checks that d*e = 1 mod
(p-1*q-1), and that dmp1, dmq1 and iqmp are set
correctly or are NULL. 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.
The cb parameter is a callback that will be invoked in the
same manner as BN_is_prime_ex(3).
RSA_check_key() is equivalent to RSA_check_key_ex()
with a NULL cb.
RSA_check_key_ex() and RSA_check_key() return 1 if rsa is a
valid RSA key, and 0 otherwise. They return -1 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).
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.
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.
RSA_check_key_ex() appeared after OpenSSL 1.0.2.
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