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RSA_set_method(3)                   OpenSSL                  RSA_set_method(3)

NAME
       RSA_set_default_method, RSA_get_default_method, RSA_set_method,
       RSA_get_method, RSA_PKCS1_SSLeay, RSA_null_method, RSA_flags,
       RSA_new_method - select RSA method
SYNOPSIS
        #include <openssl/rsa.h>
        void RSA_set_default_method(const RSA_METHOD *meth);
        RSA_METHOD *RSA_get_default_method(void);
        int RSA_set_method(RSA *rsa, const RSA_METHOD *meth);
        RSA_METHOD *RSA_get_method(const RSA *rsa);
        RSA_METHOD *RSA_PKCS1_SSLeay(void);
        RSA_METHOD *RSA_null_method(void);
        int RSA_flags(const RSA *rsa);
        RSA *RSA_new_method(RSA_METHOD *method);
DESCRIPTION
       An RSA_METHOD specifies the functions that OpenSSL uses for RSA
       operations. By modifying the method, alternative implementations such
       as hardware accelerators may be used. IMPORTANT: See the NOTES section
       for important information about how these RSA API functions are
       affected by the use of ENGINE API calls.
       Initially, the default RSA_METHOD is the OpenSSL internal
       implementation, as returned by RSA_PKCS1_SSLeay().
       RSA_set_default_method() makes meth the default method for all RSA
       structures created later. NB: This is true only whilst no ENGINE has
       been set as a default for RSA, so this function is no longer
       recommended.
       RSA_get_default_method() returns a pointer to the current default
       RSA_METHOD. However, the meaningfulness of this result is dependent on
       whether the ENGINE API is being used, so this function is no longer
       recommended.
       RSA_set_method() selects meth to perform all operations using the key
       rsa. This will replace the RSA_METHOD used by the RSA key and if the
       previous method was supplied by an ENGINE, the handle to that ENGINE
       will be released during the change. It is possible to have RSA keys
       that only work with certain RSA_METHOD implementations (eg. 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.
       RSA_get_method() 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().
       RSA_flags() returns the flags that are set for rsa's current
       RSA_METHOD. See the BUGS section.
       RSA_new_method() allocates and initializes an RSA structure so that
       engine will be used for the RSA operations. If engine is NULL, the
       default ENGINE for RSA operations is used, and if no default ENGINE is
       set, the RSA_METHOD controlled by RSA_set_default_method() is used.
       RSA_flags() returns the flags that are set for rsa's current method.
       RSA_new_method() allocates and initializes an RSA structure so that
       method will be used for the RSA operations. If method is NULL, the
       default method is used.
THE RSA_METHOD STRUCTURE
        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,
                       const unsigned char *m, unsigned int m_length,
                       unsigned char *sigret, unsigned int *siglen, const RSA *rsa);
            /* verify. For backward compatibility, this is used only
             * if (flags & RSA_FLAG_SIGN_VER)
             */
               int (*rsa_verify)(int dtype,
                       const unsigned char *m, unsigned int m_length,
                       const unsigned char *sigbuf, unsigned int siglen,
                                                                       const RSA *rsa);
            /* keygen. If NULL builtin RSA key generation will be used */
               int (*rsa_keygen)(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
        } RSA_METHOD;
RETURN VALUES
       RSA_PKCS1_SSLeay(), RSA_PKCS1_null_method(), RSA_get_default_method()
       and RSA_get_method() return pointers to the respective RSA_METHODs.
       RSA_set_default_method() returns no value.
       RSA_set_method() returns a pointer to the old RSA_METHOD implementation
       that was replaced. However, this return value should probably be
       ignored because if it was supplied by an ENGINE, the pointer could be
       invalidated at any time if the ENGINE is unloaded (in fact it could be
       unloaded as a result of the RSA_set_method() function releasing its
       handle to the ENGINE). For this reason, the return type may be replaced
       with a void declaration in a future release.
       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.
NOTES
       As of version 0.9.7, RSA_METHOD implementations are grouped together
       with other algorithmic APIs (eg. DSA_METHOD, EVP_CIPHER, etc) into
       ENGINE modules. If a default ENGINE is specified for RSA functionality
       using an ENGINE API function, that will override any RSA defaults set
       using the RSA API (ie.  RSA_set_default_method()). For this reason, the
       ENGINE API is the recommended way to control default implementations
       for use in RSA and other cryptographic algorithms.
BUGS
       The behaviour of RSA_flags() is a mis-feature 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 an
       RSA_default_flags() function (which does not currently exist).
SEE ALSO
       rsa(3), RSA_new(3)
HISTORY
       RSA_new_method() and RSA_set_default_method() appeared in SSLeay 0.8.
       RSA_get_default_method(), RSA_set_method() and RSA_get_method() as well
       as the rsa_sign and rsa_verify components of RSA_METHOD were added in
       OpenSSL 0.9.4.
       RSA_set_default_openssl_method() and RSA_get_default_openssl_method()
       replaced RSA_set_default_method() and RSA_get_default_method()
       respectively, and RSA_set_method() and RSA_new_method() were altered to
       use ENGINEs rather than RSA_METHODs during development of the engine
       version of OpenSSL 0.9.6. For 0.9.7, the handling of defaults in the
       ENGINE API was restructured so that this change was reversed, and
       behaviour of the other functions resembled more closely the previous
       behaviour. The behaviour of defaults in the ENGINE API now
       transparently overrides the behaviour of defaults in the RSA API
       without requiring changing these function prototypes.

1.0.2k                            2017-01-26                 RSA_set_method(3)