- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

DH_meth_new, DH_meth_free, DH_meth_dup, DH_meth_get0_name, DH_meth_set1_name, DH_meth_get_flags, DH_meth_set_flags, DH_meth_get0_app_data, DH_meth_set0_app_data, DH_meth_get_generate_key, DH_meth_set_generate_key, DH_meth_get_compute_key, DH_meth_set_compute_key, DH_meth_get_bn_mod_exp, DH_meth_set_bn_mod_exp, DH_meth_get_init, DH_meth_set_init, DH_meth_get_finish, DH_meth_set_finish, DH_meth_get_generate_params, DH_meth_set_generate_params - Routines to build up DH methods

# SYNOPSIS

     #include <openssl/dh.h>

     DH_METHOD *DH_meth_new(const char *name, int flags);

     void DH_meth_free(DH_METHOD *dhm);

     DH_METHOD *DH_meth_dup(const DH_METHOD *dhm);

     const char *DH_meth_get0_name(const DH_METHOD *dhm);
     int DH_meth_set1_name(DH_METHOD *dhm, const char *name);

     int DH_meth_get_flags(const DH_METHOD *dhm);
     int DH_meth_set_flags(DH_METHOD *dhm, int flags);

     void *DH_meth_get0_app_data(const DH_METHOD *dhm);
     int DH_meth_set0_app_data(DH_METHOD *dhm, void *app_data);

     int (*DH_meth_get_generate_key(const DH_METHOD *dhm))(DH *);
     int DH_meth_set_generate_key(DH_METHOD *dhm, int (*generate_key)(DH *));

     int (*DH_meth_get_compute_key(const DH_METHOD *dhm))
         (unsigned char *key, const BIGNUM *pub_key, DH *dh);
     int DH_meth_set_compute_key(DH_METHOD *dhm,
         int (*compute_key)(unsigned char *key, const BIGNUM *pub_key, DH *dh));

     int (*DH_meth_get_bn_mod_exp(const DH_METHOD *dhm))
         (const DH *dh, BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
     int DH_meth_set_bn_mod_exp(DH_METHOD *dhm,
         int (*bn_mod_exp)(const DH *dh, BIGNUM *r, const BIGNUM *a,
                           const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx,
                           BN_MONT_CTX *m_ctx));

     int (*DH_meth_get_init(const DH_METHOD *dhm))(DH *);
     int DH_meth_set_init(DH_METHOD *dhm, int (*init)(DH *));

     int (*DH_meth_get_finish(const DH_METHOD *dhm))(DH *);
     int DH_meth_set_finish(DH_METHOD *dhm, int (*finish)(DH *));

     int (*DH_meth_get_generate_params(const DH_METHOD *dhm))
         (DH *, int, int, BN_GENCB *);
     int DH_meth_set_generate_params(DH_METHOD *dhm,
         int (*generate_params)(DH *, int, int, BN_GENCB *));

# DESCRIPTION

The DH_METHOD type is a structure used for the provision of custom DH implementations. It provides a set of functions used by OpenSSL for the implementation of the various DH capabilities.

`DH_meth_new()` creates a new DH_METHOD structure. It should be given a unique name and a set of flags. The name should be a NULL terminated string, which will be duplicated and stored in the DH_METHOD object. It is the callers responsibility to free the original string. The flags will be used during the construction of a new DH object based on this DH_METHOD. Any new DH object will have those flags set by default.

`DH_meth_dup()` creates a duplicate copy of the DH_METHOD object passed as a parameter. This might be useful for creating a new DH_METHOD based on an existing one, but with some differences.

`DH_meth_free()` destroys a DH_METHOD structure and frees up any memory associated with it.

DH_meth_get0_name() will return a pointer to the name of this DH_METHOD. This is a pointer to the internal name string and so should not be freed by the caller. DH_meth_set1_name() sets the name of the DH_METHOD to name. The string is duplicated and the copy is stored in the DH_METHOD structure, so the caller remains responsible for freeing the memory associated with the name.

`DH_meth_get_flags()` returns the current value of the flags associated with this DH_METHOD. `DH_meth_set_flags()` provides the ability to set these flags.

The functions DH_meth_get0_app_data() and DH_meth_set0_app_data() provide the ability to associate implementation specific data with the DH_METHOD. It is the application's responsibility to free this data before the DH_METHOD is freed via a call to `DH_meth_free()`.

`DH_meth_get_generate_key()` and `DH_meth_set_generate_key()` get and set the function used for generating a new DH key pair respectively. This function will be called in response to the application calling `DH_generate_key()`. The parameter for the function has the same meaning as for `DH_generate_key()`.

`DH_meth_get_compute_key()` and `DH_meth_set_compute_key()` get and set the function used for computing a new DH shared secret respectively. This function will be called in response to the application calling `DH_compute_key()`. The parameters for the function have the same meaning as for `DH_compute_key()`.

`DH_meth_get_bn_mod_exp()` and `DH_meth_set_bn_mod_exp()` get and set the function used for computing the following value:

     r = a ^ p mod m

This function will be called by the default OpenSSL function for `DH_generate_key()`. The result is stored in the r parameter. This function may be NULL unless using the default generate key function, in which case it must be present.

`DH_meth_get_init()` and `DH_meth_set_init()` get and set the function used for creating a new DH instance respectively. This function will be called in response to the application calling `DH_new()` (if the current default DH_METHOD is this one) or `DH_new_method()`. The `DH_new()` and `DH_new_method()` functions will allocate the memory for the new DH object, and a pointer to this newly allocated structure will be passed as a parameter to the function. This function may be NULL.

`DH_meth_get_finish()` and `DH_meth_set_finish()` get and set the function used for destroying an instance of a DH object respectively. This function will be called in response to the application calling `DH_free()`. A pointer to the DH to be destroyed is passed as a parameter. The destroy function should be used for DH implementation specific clean up. The memory for the DH itself should not be freed by this function. This function may be NULL.

`DH_meth_get_generate_params()` and `DH_meth_set_generate_params()` get and set the function used for generating DH parameters respectively. This function will be called in response to the application calling `DH_generate_parameters_ex()` (or DH_generate_parameters()). The parameters for the function have the same meaning as for `DH_generate_parameters_ex()`. This function may be NULL.

# RETURN VALUES

`DH_meth_new()` and `DH_meth_dup()` return the newly allocated DH_METHOD object or NULL on failure.

DH_meth_get0_name() and `DH_meth_get_flags()` return the name and flags associated with the DH_METHOD respectively.

All other DH_meth_get_*() functions return the appropriate function pointer that has been set in the DH_METHOD, or NULL if no such pointer has yet been set.

DH_meth_set1_name() and all DH_meth_set_*() functions return 1 on success or 0 on failure.

# SEE ALSO

DH_new(3), DH_new(3), DH_generate_parameters(3), DH_generate_key(3), DH_set_method(3), DH_size(3), DH_get0_pqg(3)

# HISTORY

The functions described here were added in OpenSSL 1.1.0.

# COPYRIGHT

Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.