DSA_METH_NEW(3ossl)

📦

version 3.5.9 · 8 versions

3.5.9 · fedora 43, fedora 44 (latest)
3.5.9 · centos-stream 9
3.5.9 · centos-stream 10
3.5.9 · alpine 3.22
3.5.9 · alpine 3.23, alpine 3.24
3.5.8 · fedora 43
3.5.1 · fedora 43
3.5.5 · fedora 44

💖 NAME 💖

Okay so bestie, welcome to the DSA_METH_NEW(3ossl) page — that's the OpenSSL manual, and this one is all about building your own DSA methods. The official one-line summary is literally "Routines to build up DSA methods", and honestly? Iconic. Periodt.

Here's the whole squad of functions this page covers:

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

✨ SYNOPSIS ✨

First things first, you gotta pull in the header, no cap:

#include <openssl/dsa.h>

⚠️ Heads up bestie, this is important: the following functions have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

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 🌸

Okay so first, the big sad: every single function on this page is deprecated. Not me getting emotional over a deprecation notice 😭 Applications and extension implementations should instead use the OSSL_PROVIDER APIs. That's the glow-up. Fr fr.

The DSA_METHOD type is a structure used for the provision of custom DSA implementations. Think of it as a little plug-and-play kit 🎀 — it gives OpenSSL a set of functions to use for implementing all the various DSA capabilities.

DSA_meth_new() creates a new DSA_METHOD structure. You should give it 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 — so yes, it is the caller's responsibility to free the original string. The flags get used during the construction of a new DSA object based on this DSA_METHOD, and 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. Lowkey the most useful thing ever: it lets you build a new DSA_METHOD based on an existing one, but with some differences. Chef's kiss 💅

DSA_meth_free() destroys a DSA_METHOD structure and frees up any memory associated with it. And if the argument is NULL, nothing is done — no drama, no crash, we love a graceful exit 🦋

DSA_meth_get0_name() returns a pointer to the name of this DSA_METHOD. Careful bestie: it's a pointer to the internal name string, so you should not free it. DSA_meth_set1_name() sets the name of the DSA_METHOD to name. That 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() gives you the ability to set those flags.

DSA_meth_get0_app_data() and DSA_meth_set0_app_data() give you the ability to associate implementation specific data with the DSA_METHOD. And bestie, listen — it is the application's responsibility to free this data before the DSA_METHOD is freed via a call to DSA_meth_free(). Do not skip that step, I'm begging 🫶

DSA_meth_get_sign() and DSA_meth_set_sign() get and set the function used for creating a DSA signature, respectively. This function gets 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 gets 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 gets 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 gets 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 gets 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 gets 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 gets 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 — but 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 gets 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 gets 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. (Failure is not the vibe, but at least it tells you 💀)

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

All the 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 the DSA_meth_set_*() functions return 1 on success or 0 on failure.

🌈 SEE ALSO 🌈

🦋 HISTORY 🦋

The functions described here were deprecated in OpenSSL 3.0.
The functions described here were added in OpenSSL 1.1.0.

okay stay with me bestie, there's more of this page coming 👀

💖 COPYRIGHT 💖

okay bestie, legal era, but make it cute ✨

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. Like, fr fr — that's not a suggestion, that's the vibe check you have to pass 💅

You can obtain a copy in the file LICENSE in the source distribution, or at:

https://www.openssl.org/source/license.html

ngl bestie, read the actual license, it's giving required reading 📚 don't just skim it and hope for the best 😭

and that's the whole page, no cap 🫶 you made it all the way to the copyright section which means you're literally the main character of documentation reading rn 👑

this one's from the 3.5.9 era, dated 2026-09-29 — so yes, freshly dated, still iconic, still DSA_METH_NEW(3ossl) 🌸

bye bestie, go write some DSA_METHs 💖✨🎀

📦 where this page comes from

fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-14: a language model's rewrite of the original, under its terms