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RSA_SET_METHOD(3) Library Functions Manual RSA_SET_METHOD(3)

RSA_set_default_method, RSA_get_default_method, RSA_set_method, RSA_get_method, RSA_PKCS1_SSLeay, RSA_flags, RSA_new_method — select RSA method

#include <openssl/rsa.h>

void
RSA_set_default_method(const RSA_METHOD *meth);

const RSA_METHOD *
RSA_get_default_method(void);

int
RSA_set_method(RSA *rsa, const RSA_METHOD *meth);

const RSA_METHOD *
RSA_get_method(const RSA *rsa);

const RSA_METHOD *
RSA_PKCS1_SSLeay(void);

int
RSA_flags(const RSA *rsa);

RSA *
RSA_new_method(ENGINE *engine);

An RSA_METHOD object contains pointers to the functions used for RSA operations. By default, the internal implementation returned by () is used. By selecting another method, alternative implementations such as hardware accelerators may be used.

() selects meth as the default method for all RSA structures created later. If any ENGINE was registered with ENGINE_register_RSA(3) that can be successfully initialized, it overrides the default.

() returns a pointer to the current default method, even if it is actually overridded by an ENGINE.

() selects meth to perform all operations using the key rsa. This replaces the RSA_METHOD used by the RSA key, and if the previous method was supplied by an ENGINE, ENGINE_finish(3) is called on it. It is possible to have RSA keys that only work with certain RSA_METHOD implementations (e.g. from an ENGINE module that supports embedded hardware-protected keys), and in such cases attempting to change the RSA_METHOD for the key can have unexpected results.

() returns a pointer to the RSA_METHOD being used by rsa. This method may or may not be supplied by an ENGINE implementation but if it is, the return value can only be guaranteed to be valid as long as the RSA key itself is valid and does not have its implementation changed by RSA_set_method().

() returns the flags that are set for the current RSA_METHOD of rsa. See the BUGS section.

() allocates and initializes an RSA structure so that engine is used for the RSA operations. If engine is NULL, ENGINE_get_default_RSA(3) is used. If that returns NULL, the default method controlled by RSA_set_default_method() is used.

The RSA_METHOD structure is defined as follows:

typedef struct rsa_meth_st
{
     /* name of the implementation */
	const char *name;

     /* encrypt */
	int (*rsa_pub_enc)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* verify arbitrary data */
	int (*rsa_pub_dec)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* sign arbitrary data */
	int (*rsa_priv_enc)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* decrypt */
	int (*rsa_priv_dec)(int flen, unsigned char *from,
          unsigned char *to, RSA *rsa, int padding);

     /* compute r0 = r0 ^ I mod rsa->n (May be NULL for some
                                        implementations) */
	int (*rsa_mod_exp)(BIGNUM *r0, BIGNUM *I, RSA *rsa);

     /* compute r = a ^ p mod m (May be NULL for some implementations) */
	int (*bn_mod_exp)(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);

     /* called at RSA_new */
	int (*init)(RSA *rsa);

     /* called at RSA_free */
	int (*finish)(RSA *rsa);

     /* RSA_FLAG_EXT_PKEY        - rsa_mod_exp is called for private key
      *                            operations, even if p,q,dmp1,dmq1,iqmp
      *                            are NULL
      * RSA_FLAG_SIGN_VER        - enable rsa_sign and rsa_verify
      * RSA_METHOD_FLAG_NO_CHECK - don't check pub/private match
      */
	int flags;

	char *app_data; /* ?? */

     /* sign. For backward compatibility, this is used only
      * if (flags & RSA_FLAG_SIGN_VER)
      */
	int (*rsa_sign)(int type, unsigned char *m, unsigned int m_len,
           unsigned char *sigret, unsigned int *siglen, RSA *rsa);

     /* verify. For backward compatibility, this is used only
      * if (flags & RSA_FLAG_SIGN_VER)
      */
	int (*rsa_verify)(int type, unsigned char *m, unsigned int m_len,
           unsigned char *sigbuf, unsigned int siglen, RSA *rsa);

} RSA_METHOD;

RSA_PKCS1_SSLeay(), RSA_get_default_method(), and RSA_get_method() return pointers to the respective RSA_METHOD.

RSA_set_method() returns 1 on success or 0 on failure. Currently, it cannot fail.

RSA_new_method() returns NULL and sets an error code that can be obtained by ERR_get_error(3) if the allocation fails. Otherwise it returns a pointer to the newly allocated structure.

ENGINE_get_default_RSA(3), ENGINE_register_RSA(3), ENGINE_set_default_RSA(3), RSA_meth_new(3), RSA_new(3)

RSA_set_default_method(), RSA_PKCS1_SSLeay(), and RSA_new_method() first appeared in SSLeay 0.8.0. RSA_flags() first appeared in SSLeay 0.9.0. These functions have been available since OpenBSD 2.4.

RSA_get_default_method(), RSA_set_method(), and RSA_get_method() as well as the rsa_sign and rsa_verify components of RSA_METHOD first appeared in OpenSSL 0.9.4 and have been available since OpenBSD 2.6.

The behaviour of RSA_flags() is a misfeature that is left as-is for now to avoid creating compatibility problems. RSA functionality, such as the encryption functions, are controlled by the flags value in the RSA key itself, not by the flags value in the RSA_METHOD attached to the RSA key (which is what this function returns). If the flags element of an RSA key is changed, the changes will be honoured by RSA functionality but will not be reflected in the return value of the RSA_flags() function - in effect RSA_flags() behaves more like a RSA_default_flags() function, which does not currently exist.

April 18, 2018 OpenBSD-6.4