=pod

=head1 NAME

RSA_set_default_method, RSA_get_default_method, RSA_set_method,
RSA_get_method, RSA_PKCS1_SSLeay, RSA_PKCS1_RSAref,
RSA_null_method, RSA_flags, RSA_new_method - select RSA method

=head1 SYNOPSIS

 #include <openssl/rsa.h>
 #include <openssl/engine.h>

 void RSA_set_default_openssl_method(RSA_METHOD *meth);

 RSA_METHOD *RSA_get_default_openssl_method(void);

 RSA_METHOD *RSA_set_method(RSA *rsa, ENGINE *engine);

 RSA_METHOD *RSA_get_method(RSA *rsa);

 RSA_METHOD *RSA_PKCS1_SSLeay(void);

 RSA_METHOD *RSA_PKCS1_RSAref(void);

 RSA_METHOD *RSA_null_method(void);

 int RSA_flags(RSA *rsa);

 RSA *RSA_new_method(ENGINE *engine);

=head1 DESCRIPTION

An B<RSA_METHOD> specifies the functions that OpenSSL uses for RSA
operations. By modifying the method, alternative implementations
such as hardware accelerators may be used.

Initially, the default is to use the OpenSSL internal implementation,
unless OpenSSL was configured with the C<rsaref> or C<-DRSA_NULL>
options. RSA_PKCS1_SSLeay() returns a pointer to that method.

RSA_PKCS1_RSAref() returns a pointer to a method that uses the RSAref
library. This is the default method in the C<rsaref> configuration;
the function is not available in other configurations.
RSA_null_method() returns a pointer to a method that does not support
the RSA transformation. It is the default if OpenSSL is compiled with
C<-DRSA_NULL>. These methods may be useful in the USA because of a
patent on the RSA cryptosystem.

RSA_set_default_openssl_method() makes B<meth> the default method for all B<RSA>
structures created later. B<NB:> This is true only whilst the default engine
for RSA operations remains as "openssl". ENGINEs provide an
encapsulation for implementations of one or more algorithms at a time, and all
the RSA functions mentioned here operate within the scope of the default
"openssl" engine.

RSA_get_default_openssl_method() returns a pointer to the current default
method for the "openssl" engine.

RSA_set_method() selects B<engine> for all operations using the key
B<rsa>.

RSA_get_method() returns a pointer to the RSA_METHOD from the currently
selected ENGINE for B<rsa>.

RSA_flags() returns the B<flags> that are set for B<rsa>'s current method.

RSA_new_method() allocates and initializes an RSA structure so that
B<engine> will be used for the RSA operations. If B<engine> is NULL,
the default engine for RSA operations is used.

=head1 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;

=head1 RETURN VALUES

RSA_PKCS1_SSLeay(), RSA_PKCS1_RSAref(), RSA_PKCS1_null_method(),
RSA_get_default_openssl_method() and RSA_get_method() return pointers to
the respective RSA_METHODs.

RSA_set_default_openssl_method() returns no value.

RSA_set_method() selects B<engine> as the engine that will be responsible for
all operations using the structure B<rsa>. If this function completes successfully,
then the B<rsa> structure will have its own functional reference of B<engine>, so
the caller should remember to free their own reference to B<engine> when they are
finished with it. NB: An ENGINE's RSA_METHOD can be retrieved (or set) by
ENGINE_get_RSA() or ENGINE_set_RSA().

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

=head1 SEE ALSO

L<rsa(3)|rsa(3)>, L<RSA_new(3)|RSA_new(3)>

=head1 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 B<ENGINE>s
rather than B<DH_METHOD>s during development of OpenSSL 0.9.6.

=cut