DH_set_method(3)

NAME
DH_set_default_method, DH_get_default_method, DH_set_method, DH_new_method, DH_OpenSSL - select DH method

SYNOPSIS
 #include <openssl/dh.h>

 void DH_set_default_method(DH_METHOD *meth);

 DH_METHOD *DH_get_default_method(void);

 DH_METHOD *DH_set_method(DH *dh, DH_METHOD *meth);

 DH *DH_new_method(DH_METHOD *meth);

 DH_METHOD *DH_OpenSSL(void);

DESCRIPTION
A DH_METHOD specifies the functions that OpenSSL uses for Diffie-Hellman operations. By modifying the method, alternative implementations such as hardware accelerators may be used.

Initially, the default is to use the OpenSSL internal implementation. DH_OpenSSL() returns a pointer to that method.

DH_set_default_method() makes meth the default method for all DH structures created later.

DH_get_default_method() returns a pointer to the current default method.

DH_set_method() selects meth for all operations using the structure dh.

DH_new_method() allocates and initializes a DH structure so that method will be used for the DH operations. If method is NULL, the default method is used.

THE DH_METHOD STRUCTURE
 typedef struct dh_meth_st
 {
     /* name of the implementation */
        const char *name;

     /* generate private and public DH values for key agreement */
        int (*generate_key)(DH *dh);

     /* compute shared secret */
        int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh);

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

     /* called at DH_new */
        int (*init)(DH *dh);

     /* called at DH_free */
        int (*finish)(DH *dh);

        int flags;

        char *app_data; /* ?? */

 } DH_METHOD;

RETURN VALUES
DH_OpenSSL() and DH_get_default_method() return pointers to the respective DH_METHODs.

DH_set_default_method() returns no value.

DH_set_method() returns a pointer to the DH_METHOD previously associated with dh.

DH_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.

SEE ALSO
dh(3), DH_new(3)

HISTORY
DH_set_default_method(), DH_get_default_method(), DH_set_method(), DH_new_method() and DH_OpenSSL() were added in OpenSSL 0.9.4.