RSA_get_method (3)

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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 specifies the functions that OpenSSL uses for operations. By modifying the method, alternative implementations such as hardware accelerators may be used. See the section for important information about how these functions are affected by the use of calls.

Initially, the default

is the OpenSSL internal implementation, as returned by RSA_PKCS1_SSLeay().

RSA_set_default_method() makes meth the default method for all

structures created later. : This is true only whilst no has been set as a default for so this function is no longer recommended.

RSA_get_default_method() returns a pointer to the current default

However, the meaningfulness of this result is dependent on whether the 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

used by the key and if the previous method was supplied by an the handle to that will be released during the change. It is possible to have keys that only work with certain implementations (eg. from an module that supports embedded hardware-protected keys), and in such cases attempting to change the for the key can have unexpected results.

RSA_get_method() returns a pointer to the

being used by rsa. This method may or may not be supplied by an implementation, but if it is, the return value can only be guaranteed to be valid as long as the 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

See the section.

RSA_new_method() allocates and initializes an

structure so that engine will be used for the operations. If engine is the default for operations is used, and if no default is set, the 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

structure so that method will be used for the operations. If method is , 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

implementation that was replaced. However, this return value should probably be ignored because if it was supplied by an the pointer could be invalidated at any time if the is unloaded (in fact it could be unloaded as a result of the RSA_set_method() function releasing its handle to the ). For this reason, the return type may be replaced with a void declaration in a future release.

RSA_new_method() returns

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, implementations are grouped together with other algorithmic APIs (eg. etc) into modules. If a default is specified for functionality using an function, that will override any defaults set using the (ie. RSA_set_default_method()). For this reason, the is the recommended way to control default implementations for use in 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. functionality, such as the encryption functions, are controlled by the flags value in the key itself, not by the flags value in the attached to the key (which is what this function returns). If the flags element of an key is changed, the changes will be honoured by 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 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

s rather than s during development of the engine version of OpenSSL 0.9.6. For 0.9.7, the handling of defaults in the 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 now transparently overrides the behaviour of defaults in the without requiring changing these function prototypes.