DH_SET_METHOD(3)           Library Functions Manual           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(const DH_METHOD *meth);

     const DH_METHOD *
     DH_get_default_method(void);

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

     DH *
     DH_new_method(ENGINE *engine);

     const DH_METHOD *
     DH_OpenSSL(void);

DESCRIPTION
     A DH_METHOD object contains pointers to the functions used for Diffie-
     Hellman operations.  By default, the internal implementation returned by
     DH_OpenSSL() is used.  By selecting another method, alternative
     implementations such as hardware accelerators may be used.

     DH_set_default_method() selects meth as 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 to perform all operations using the key dh.
     This replaces the DH_METHOD used by the dh key.  It is possible to have
     DH keys that only work with certain DH_METHOD implementations, and in
     such cases attempting to change the DH_METHOD for the key can have
     unexpected results.

     DH_new_method() allocates and initializes a DH structure.  The engine
     argument is ignored and the default method controlled by
     DH_set_default_method() is used.

     The DH_METHOD structure is defined as follows:

     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_METHOD.

     DH_set_method() returns 1 on success or 0 on failure.  Currently, it
     cannot fail.

     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_new(3)

HISTORY
     DH_set_default_method(), DH_get_default_method(), DH_set_method(),
     DH_new_method() and DH_OpenSSL() first appeared in OpenSSL 0.9.5 and have
     been available since OpenBSD 2.7.

Linux 6.8.2-arch2-1            November 19, 2023           Linux 6.8.2-arch2-1