.Dd $Mdocdate: November 5 2016 $
.Dt DSA 3
.Os
.Sh NAME
.Nm dsa
.Nd Digital Signature Algorithm
.Sh SYNOPSIS
.In openssl/dsa.h
.In openssl/engine.h
.Ft DSA *
.Fn DSA_new void
.Ft void
.Fo DSA_free
.Fa "DSA *dsa"
.Fc
.Ft int
.Fo DSA_size
.Fa "const DSA *dsa"
.Fc
.Ft DSA *
.Fo DSA_generate_parameters
.Fa "int bits"
.Fa "unsigned char *seed"
.Fa "int seed_len"
.Fa "int *counter_ret"
.Fa "unsigned long *h_ret"
.Fa "void (*callback)(int, int, void *)"
.Fa "void *cb_arg"
.Fc
.Ft DH *
.Fo DSA_dup_DH
.Fa "const DSA *r"
.Fc
.Ft int
.Fo DSA_generate_key
.Fa "DSA *dsa"
.Fc
.Ft int
.Fo DSA_sign
.Fa "int dummy"
.Fa "const unsigned char *dgst"
.Fa "int len"
.Fa "unsigned char *sigret"
.Fa "unsigned int *siglen"
.Fa "DSA *dsa"
.Fc
.Ft int
.Fo DSA_sign_setup
.Fa "DSA *dsa"
.Fa "BN_CTX *ctx"
.Fa "BIGNUM **kinvp"
.Fa "BIGNUM **rp"
.Fc
.Ft int
.Fo DSA_verify
.Fa "int dummy"
.Fa "const unsigned char *dgst"
.Fa "int len"
.Fa "const unsigned char *sigbuf"
.Fa "int siglen"
.Fa "DSA *dsa"
.Fc
.Ft void
.Fo DSA_set_default_method
.Fa "const DSA_METHOD *meth"
.Fc
.Ft const DSA_METHOD *
.Fn DSA_get_default_method void
.Ft int
.Fo DSA_set_method
.Fa "DSA *dsa"
.Fa "const DSA_METHOD *meth"
.Fc
.Ft DSA *
.Fo DSA_new_method
.Fa "ENGINE *engine"
.Fc
.Ft const DSA_METHOD *
.Fn DSA_OpenSSL void
.Ft int
.Fo DSA_get_ex_new_index
.Fa "long argl"
.Fa "char *argp"
.Fa "int (*new_func)()"
.Fa "int (*dup_func)()"
.Fa "void (*free_func)()"
.Fc
.Ft int
.Fo DSA_set_ex_data
.Fa "DSA *d"
.Fa "int idx"
.Fa "char *arg"
.Fc
.Ft char *
.Fo DSA_get_ex_data
.Fa "DSA *d"
.Fa "int idx"
.Fc
.Ft DSA_SIG *
.Fn DSA_SIG_new void
.Ft void
.Fo DSA_SIG_free
.Fa "DSA_SIG *a"
.Fc
.Ft int
.Fo i2d_DSA_SIG
.Fa "const DSA_SIG *a"
.Fa "unsigned char **pp"
.Fc
.Ft DSA_SIG *
.Fo d2i_DSA_SIG
.Fa "DSA_SIG **v"
.Fa "unsigned char **pp"
.Fa "long length"
.Fc
.Ft DSA_SIG *
.Fo DSA_do_sign
.Fa "const unsigned char *dgst"
.Fa "int dlen"
.Fa "DSA *dsa"
.Fc
.Ft int
.Fo DSA_do_verify
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "DSA_SIG *sig"
.Fa "DSA *dsa"
.Fc
.Ft DSA *
.Fo d2i_DSAPublicKey
.Fa "DSA **a"
.Fa "unsigned char **pp"
.Fa "long length"
.Fc
.Ft DSA *
.Fo d2i_DSAPrivateKey
.Fa "DSA **a"
.Fa "unsigned char **pp"
.Fa "long length"
.Fc
.Ft DSA *
.Fo d2i_DSAparams
.Fa "DSA **a"
.Fa "unsigned char **pp"
.Fa "long length"
.Fc
.Ft int
.Fo i2d_DSAPublicKey
.Fa "const DSA *a"
.Fa "unsigned char **pp"
.Fc
.Ft int
.Fo i2d_DSAPrivateKey
.Fa "const DSA *a"
.Fa "unsigned char **pp"
.Fc
.Ft int
.Fo i2d_DSAparams
.Fa "const DSA *a"
.Fa "unsigned char **pp"
.Fc
.Ft int
.Fo DSAparams_print
.Fa "BIO *bp"
.Fa "const DSA *x"
.Fc
.Ft int
.Fo DSAparams_print_fp
.Fa "FILE *fp"
.Fa "const DSA *x"
.Fc
.Ft int
.Fo DSA_print
.Fa "BIO *bp"
.Fa "const DSA *x"
.Fa "int off"
.Fc
.Ft int
.Fo DSA_print_fp
.Fa "FILE *bp"
.Fa "const DSA *x"
.Fa "int off"
.Fc
.Sh DESCRIPTION
These functions implement the Digital Signature Algorithm (DSA).
The generation of shared DSA parameters is described in
.Xr DSA_generate_parameters 3 ;
.Xr DSA_generate_key 3
describes how to generate a signature key.
Signature generation and verification are described in
.Xr DSA_sign 3 .
.Pp
The
.Vt DSA
structure consists of several BIGNUM components.
.Bd -literal
typedef 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;
.Ed
.Pp
In public keys,
.Fa priv_key
is
.Dv NULL .
.Pp
Note that DSA keys may use non-standard
.Vt DSA_METHOD
implementations, either directly or by the use of
.Vt ENGINE
modules.
In some cases (eg. an
.Vt ENGINE
providing support for hardware-embedded keys), these
.Vt 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
.Vt DSA
structure elements directly and instead use API functions to query
or modify keys.
.Sh SEE ALSO
.Xr bn 3 ,
.Xr dh 3 ,
.Xr DSA_dup_DH 3 ,
.Xr DSA_generate_key 3 ,
.Xr DSA_generate_parameters 3 ,
.Xr DSA_get_ex_new_index 3 ,
.Xr DSA_new 3 ,
.Xr DSA_set_method 3 ,
.Xr DSA_sign 3 ,
.Xr DSA_size 3 ,
.Xr engine 3 ,
.Xr err 3 ,
.Xr rsa 3 ,
.Xr RSA_print 3
.Sh STANDARDS
US Federal Information Processing Standard FIPS 186 (Digital Signature
Standard, DSS), ANSI X9.30