dh(3)                               OpenSSL                              dh(3)



NAME
       dh - Diffie-Hellman key agreement

LIBRARY
       libcrypto, -lcrypto

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 val-
       ues will not be used by the implementation or may be used for alterna-
       tive data storage. For this reason, applications should generally avoid
       using DH structure elements directly and instead use API functions to
       query or modify keys.

SEE ALSO
       openssl_dhparam(1), openssl_bn(3), openssl_dsa(3), openssl_err(3),
       openssl_rand(3), openssl_rsa(3), engine(3), DH_set_method(3),
       DH_new(3), DH_get_ex_new_index(3), DH_generate_parameters(3), DH_com-
       pute_key(3), d2i_DHparams(3), RSA_print(3)



0.9.9-dev                         2003-07-24                             dh(3)

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