dsa - Digital Signature Algorithm

 #include <openssl/dsa.h>
 #include <openssl/engine.h>

 DSA *  DSA_new(void);
 void   DSA_free(DSA *dsa);

 int    DSA_size(const DSA *dsa);

 DSA *  DSA_generate_parameters(int bits, unsigned char *seed,
                int seed_len, int *counter_ret, unsigned long *h_ret,
                void (*callback)(int, int, void *), void *cb_arg);

 DH *   DSA_dup_DH(const DSA *r);

 int    DSA_generate_key(DSA *dsa);

 int    DSA_sign(int dummy, const unsigned char *dgst, int len,
                unsigned char *sigret, unsigned int *siglen, DSA *dsa);
 int    DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp,
                BIGNUM **rp);
 int    DSA_verify(int dummy, const unsigned char *dgst, int len,
                const unsigned char *sigbuf, int siglen, DSA *dsa);

 void DSA_set_default_method(const DSA_METHOD *meth);
 const DSA_METHOD *DSA_get_default_method(void);
 int DSA_set_method(DSA *dsa, const DSA_METHOD *meth);
 DSA *DSA_new_method(ENGINE *engine);
 const DSA_METHOD *DSA_OpenSSL(void);

 int DSA_get_ex_new_index(long argl, char *argp, int (*new_func)(),
             int (*dup_func)(), void (*free_func)());
 int DSA_set_ex_data(DSA *d, int idx, char *arg);
 char *DSA_get_ex_data(DSA *d, int idx);

 DSA_SIG *DSA_SIG_new(void);
 void   DSA_SIG_free(DSA_SIG *a);
 int    i2d_DSA_SIG(const DSA_SIG *a, unsigned char **pp);
 DSA_SIG *d2i_DSA_SIG(DSA_SIG **v, unsigned char **pp, long length);

 DSA_SIG *DSA_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
 int    DSA_do_verify(const unsigned char *dgst, int dgst_len,
             DSA_SIG *sig, DSA *dsa);

 DSA *  d2i_DSAPublicKey(DSA **a, unsigned char **pp, long length);
 DSA *  d2i_DSAPrivateKey(DSA **a, unsigned char **pp, long length);
 DSA *  d2i_DSAparams(DSA **a, unsigned char **pp, long length);
 int    i2d_DSAPublicKey(const DSA *a, unsigned char **pp);
 int    i2d_DSAPrivateKey(const DSA *a, unsigned char **pp);
 int    i2d_DSAparams(const DSA *a,unsigned char **pp);

 int    DSAparams_print(BIO *bp, const DSA *x);
 int    DSAparams_print_fp(FILE *fp, const DSA *x);
 int    DSA_print(BIO *bp, const DSA *x, int off);
 int    DSA_print_fp(FILE *bp, const DSA *x, int off);

These functions implement the Digital Signature Algorithm (DSA). The generation of shared DSA parameters is described in DSA_generate_parameters(3); DSA_generate_key(3) describes how to generate a signature key. Signature generation and verification are described in DSA_sign(3).

The DSA structure consists of several BIGNUM components.

 struct
        {
        BIGNUM *p;              // prime number (public)
        BIGNUM *q;              // 160-bit subprime, q | p-1 (public)
        BIGNUM *g;              // generator of subgroup (public)
        BIGNUM *priv_key;       // private key x
        BIGNUM *pub_key;        // public key y = g^x
        // ...
        }
 DSA;

In public keys, priv_key is NULL.

Note that DSA keys may use non-standard DSA_METHOD implementations, either directly or by the use of ENGINE modules. In some cases (eg. an ENGINE providing support for hardware-embedded keys), these BIGNUM values will not be used by the implementation or may be used for alternative data storage. For this reason, applications should generally avoid using DSA structure elements directly and instead use API functions to query or modify keys.

US Federal Information Processing Standard FIPS 186 (Digital Signature Standard, DSS), ANSI X9.30

bn(3), dh(3), err(3), rand(3), rsa(3), sha(3), engine(3), DSA_new(3), DSA_size(3), DSA_generate_parameters(3), DSA_dup_DH(3), DSA_generate_key(3), DSA_sign(3), DSA_set_method(3), DSA_get_ex_new_index(3), RSA_print(3)