dh(3)								      OpenSSL								     dh(3)

NAME

       dh - Diffie-Hellman key agreement

SYNOPSIS

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

	DH *   DH_new(void);
	void   DH_free(DH *dh);

	int    DH_size(const DH *dh);

	DH *   DH_generate_parameters(int prime_len, int generator,
		       void (*callback)(int, int, void *), void *cb_arg);
	int    DH_check(const DH *dh, int *codes);

	int    DH_generate_key(DH *dh);
	int    DH_compute_key(unsigned char *key, BIGNUM *pub_key, DH *dh);

	void DH_set_default_method(const DH_METHOD *meth);
	const DH_METHOD *DH_get_default_method(void);
	int DH_set_method(DH *dh, const DH_METHOD *meth);
	DH *DH_new_method(ENGINE *engine);
	const DH_METHOD *DH_OpenSSL(void);

	int DH_get_ex_new_index(long argl, char *argp, int (*new_func)(),
		    int (*dup_func)(), void (*free_func)());
	int DH_set_ex_data(DH *d, int idx, char *arg);
	char *DH_get_ex_data(DH *d, int idx);

	DH *   d2i_DHparams(DH **a, unsigned char **pp, long length);
	int    i2d_DHparams(const DH *a, unsigned char **pp);

	int    DHparams_print_fp(FILE *fp, const DH *x);
	int    DHparams_print(BIO *bp, const DH *x);

DESCRIPTION

       These functions implement the Diffie-Hellman key agreement protocol.  The generation of shared DH parameters is described in DH_gener-
       ate_parameters(3); DH_generate_key(3) describes how to perform a key agreement.

       The DH structure consists of several BIGNUM components.

	struct
	       {
	       BIGNUM *p;	       // prime number (shared)
	       BIGNUM *g;	       // generator of Z_p (shared)
	       BIGNUM *priv_key;       // private DH value x
	       BIGNUM *pub_key;        // public DH value g^x
	       // ...
	       };
	DH

       Note that DH keys may use non-standard DH_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 alter-
       native data storage. For this reason, applications should generally avoid using DH structure elements directly and instead use API func-
       tions to query or modify keys.

SEE ALSO

       dhparam(1), bn(3), dsa(3), err(3), rand(3), rsa(3), engine(3), DH_set_method(3), DH_new(3), DH_get_ex_new_index(3), DH_generate_parame-
       ters(3), DH_compute_key(3), d2i_DHparams(3), RSA_print(3)

0.9.7a								    2002-08-05								     dh(3)