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 inter-
       nal 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 cur-
       rent default RSA_METHOD. However, the meaningfulness of
       this result is dependant 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 sup-
       plied 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 struc-
       ture 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 struc-
       ture 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, 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;

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 sup-
       plied 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 alloca-
       tion 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 implemen-
       tations for use in RSA and other cryptographic algo-
       rithms.

BUGS
       The behaviour of RSA_flags() is a mis-feature that is
       left as-is for now to avoid creating compatibility prob-
       lems. RSA functionality, such as the encryption func-
       tions, 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 dur-
       ing 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.



0.9.7c                     2002-09-25         RSA_set_method(3)
