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DESCRIPTION

RSA_new() allocates and initializes an RSA structure, setting the reference count to 1. It is equivalent to calling RSA_new_method(3) with a NULL argument.

RSAPrivateKey_dup() calls RSA_new() and copies the public and private key components from rsa into the new structure. RSAPublicKey_dup() does the same except that it copies the public key components only.

RSA_up_ref() increments the reference count by 1.

RSA_free() decrements the reference count by 1. If it reaches 0, it calls the optional finish function set up with RSA_meth_set_finish(3), calls ENGINE_finish(3) if rsa uses an engine, and frees the RSA structure and its components. The key is erased before the memory is returned to the system. If rsa is a NULL pointer, no action occurs.

The RSA structure consists of several BIGNUM components. It can contain public as well as private RSA keys:

typedef struct {
	BIGNUM *n;		// public modulus
	BIGNUM *e;		// public exponent
	BIGNUM *d;		// private exponent
	BIGNUM *p;		// secret prime factor
	BIGNUM *q;		// secret prime factor
	BIGNUM *dmp1;		// d mod (p-1)
	BIGNUM *dmq1;		// d mod (q-1)
	BIGNUM *iqmp;		// q^-1 mod p
	// ...
} RSA;

In public keys, the private exponent d and the related secret values p, q, dmp1, dmp2, and iqmp are NULL.

p, q, dmp1, dmq1, and iqmp may be NULL in private keys, but the RSA operations are much faster when these values are available.

Note that RSA keys may use non-standard RSA_METHOD implementations, either directly or by the use of ENGINE modules. In some cases (e.g. an ENGINE providing support for hardware-embedded keys), these BIGNUM values will not be used by the implementation or may be used for alternative data storage. For this reason, applications should generally avoid using RSA structure elements directly and instead use API functions to query or modify keys.