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

# NAME

DSA_meth_new, DSA_meth_free, DSA_meth_dup, DSA_meth_get0_name, DSA_meth_set1_name, DSA_meth_get_flags, DSA_meth_set_flags, DSA_meth_get0_app_data, DSA_meth_set0_app_data, DSA_meth_get_sign, DSA_meth_set_sign, DSA_meth_get_sign_setup, DSA_meth_set_sign_setup, DSA_meth_get_verify, DSA_meth_set_verify, DSA_meth_get_mod_exp, DSA_meth_set_mod_exp, DSA_meth_get_bn_mod_exp, DSA_meth_set_bn_mod_exp, DSA_meth_get_init, DSA_meth_set_init, DSA_meth_get_finish, DSA_meth_set_finish, DSA_meth_get_paramgen, DSA_meth_set_paramgen, DSA_meth_get_keygen, DSA_meth_set_keygen - Routines to build up DSA methods

# SYNOPSIS

     #include <openssl/dsa.h>

     DSA_METHOD *DSA_meth_new(const char *name, int flags);

     void DSA_meth_free(DSA_METHOD *dsam);

     DSA_METHOD *DSA_meth_dup(const DSA_METHOD *meth);

     const char *DSA_meth_get0_name(const DSA_METHOD *dsam);
     int DSA_meth_set1_name(DSA_METHOD *dsam, const char *name);

     int DSA_meth_get_flags(const DSA_METHOD *dsam);
     int DSA_meth_set_flags(DSA_METHOD *dsam, int flags);

     void *DSA_meth_get0_app_data(const DSA_METHOD *dsam);
     int DSA_meth_set0_app_data(DSA_METHOD *dsam, void *app_data);

     DSA_SIG *(*DSA_meth_get_sign(const DSA_METHOD *dsam))(const unsigned char *,
                                                           int, DSA *);
     int DSA_meth_set_sign(DSA_METHOD *dsam, DSA_SIG *(*sign)(const unsigned char *,
                                                              int, DSA *));

     int (*DSA_meth_get_sign_setup(const DSA_METHOD *dsam))(DSA *, BN_CTX *,$
                                                            BIGNUM **, BIGNUM **);
     int DSA_meth_set_sign_setup(DSA_METHOD *dsam, int (*sign_setup)(DSA *, BN_CTX *,
                                                                     BIGNUM **, BIGNUM **));

     int (*DSA_meth_get_verify(const DSA_METHOD *dsam))(const unsigned char *,
                                                        int, DSA_SIG *, DSA *);
     int DSA_meth_set_verify(DSA_METHOD *dsam, int (*verify)(const unsigned char *,
                                                             int, DSA_SIG *, DSA *));

     int (*DSA_meth_get_mod_exp(const DSA_METHOD *dsam))(DSA *dsa, BIGNUM *rr, BIGNUM *a1,
                                                         BIGNUM *p1, BIGNUM *a2, BIGNUM *p2,
                                                         BIGNUM *m, BN_CTX *ctx,
                                                         BN_MONT_CTX *in_mont);
     int DSA_meth_set_mod_exp(DSA_METHOD *dsam, int (*mod_exp)(DSA *dsa, BIGNUM *rr,
                                                               BIGNUM *a1, BIGNUM *p1,
                                                               BIGNUM *a2, BIGNUM *p2,
                                                               BIGNUM *m, BN_CTX *ctx,
                                                               BN_MONT_CTX *mont));

     int (*DSA_meth_get_bn_mod_exp(const DSA_METHOD *dsam))(DSA *dsa, BIGNUM *r, BIGNUM *a,
                                                            const BIGNUM *p, const BIGNUM *m,
                                                            BN_CTX *ctx, BN_MONT_CTX *mont);
     int DSA_meth_set_bn_mod_exp(DSA_METHOD *dsam, int (*bn_mod_exp)(DSA *dsa,
                                                                     BIGNUM *r,
                                                                     BIGNUM *a,
                                                                     const BIGNUM *p,
                                                                     const BIGNUM *m,
                                                                     BN_CTX *ctx,
                                                                     BN_MONT_CTX *mont));

     int (*DSA_meth_get_init(const DSA_METHOD *dsam))(DSA *);
     int DSA_meth_set_init(DSA_METHOD *dsam, int (*init)(DSA *));

     int (*DSA_meth_get_finish(const DSA_METHOD *dsam))(DSA *);
     int DSA_meth_set_finish(DSA_METHOD *dsam, int (*finish)(DSA *));

     int (*DSA_meth_get_paramgen(const DSA_METHOD *dsam))(DSA *, int,
                                                          const unsigned char *,
                                                          int, int *, unsigned long *,
                                                          BN_GENCB *);
     int DSA_meth_set_paramgen(DSA_METHOD *dsam,
                               int (*paramgen)(DSA *, int, const unsigned char *,
                                               int, int *, unsigned long *, BN_GENCB *));

     int (*DSA_meth_get_keygen(const DSA_METHOD *dsam))(DSA *);
     int DSA_meth_set_keygen(DSA_METHOD *dsam, int (*keygen)(DSA *));

# DESCRIPTION

The DSA_METHOD type is a structure used for the provision of custom DSA implementations. It provides a set of functions used by OpenSSL for the implementation of the various DSA capabilities. See the the dsa manpage page for more information.

`DSA_meth_new()` creates a new DSA_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 DSA_METHOD object. It is the callers responsibility to free the original string. The flags will be used during the construction of a new DSA object based on this DSA_METHOD. Any new DSA object will have those flags set by default.

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

`DSA_meth_free()` destroys a DSA_METHOD structure and frees up any memory associated with it.

DSA_meth_get0_name() will return a pointer to the name of this DSA_METHOD. This is a pointer to the internal name string and so should not be freed by the caller. DSA_meth_set1_name() sets the name of the DSA_METHOD to name. The string is duplicated and the copy is stored in the DSA_METHOD structure, so the caller remains responsible for freeing the memory associated with the name.

`DSA_meth_get_flags()` returns the current value of the flags associated with this DSA_METHOD. `DSA_meth_set_flags()` provides the ability to set these flags.

The functions DSA_meth_get0_app_data() and DSA_meth_set0_app_data() provide the ability to associate implementation specific data with the DSA_METHOD. It is the application's responsibility to free this data before the DSA_METHOD is freed via a call to `DSA_meth_free()`.

`DSA_meth_get_sign()` and `DSA_meth_set_sign()` get and set the function used for creating a DSA signature respectively. This function will be called in response to the application calling `DSA_do_sign()` (or DSA_sign()). The parameters for the function have the same meaning as for `DSA_do_sign()`.

`DSA_meth_get_sign_setup()` and `DSA_meth_set_sign_setup()` get and set the function used for precalculating the DSA signature values k^-1 and r. This function will be called in response to the application calling `DSA_sign_setup()`. The parameters for the function have the same meaning as for `DSA_sign_setup()`.

`DSA_meth_get_verify()` and `DSA_meth_set_verify()` get and set the function used for verifying a DSA signature respectively. This function will be called in response to the application calling `DSA_do_verify()` (or DSA_verify()). The parameters for the function have the same meaning as for `DSA_do_verify()`.

`DSA_meth_get_mod_exp()` and `DSA_meth_set_mod_exp()` get and set the function used for computing the following value:

     rr = a1^p1 * a2^p2 mod m

This function will be called by the default OpenSSL method during verification of a DSA signature. The result is stored in the rr parameter. This function may be NULL.

`DSA_meth_get_bn_mod_exp()` and `DSA_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 `DSA_sign_setup()`. The result is stored in the r parameter. This function may be NULL.

`DSA_meth_get_init()` and `DSA_meth_set_init()` get and set the function used for creating a new DSA instance respectively. This function will be called in response to the application calling `DSA_new()` (if the current default DSA_METHOD is this one) or `DSA_new_method()`. The `DSA_new()` and `DSA_new_method()` functions will allocate the memory for the new DSA object, and a pointer to this newly allocated structure will be passed as a parameter to the function. This function may be NULL.

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

`DSA_meth_get_paramgen()` and `DSA_meth_set_paramgen()` get and set the function used for generating DSA parameters respectively. This function will be called in response to the application calling `DSA_generate_parameters_ex()` (or DSA_generate_parameters()). The parameters for the function have the same meaning as for `DSA_generate_parameters_ex()`.

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

# RETURN VALUES

`DSA_meth_new()` and `DSA_meth_dup()` return the newly allocated DSA_METHOD object or NULL on failure.

DSA_meth_get0_name() and `DSA_meth_get_flags()` return the name and flags associated with the DSA_METHOD respectively.

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

DSA_meth_set1_name() and all DSA_meth_set_*() functions return 1 on success or 0 on failure.

# SEE ALSO

DSA_new(3), DSA_new(3), DSA_generate_parameters(3), DSA_generate_key(3), DSA_dup_DH(3), DSA_do_sign(3), DSA_set_method(3), DSA_SIG_new(3), DSA_sign(3), DSA_size(3), DSA_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.