dh(3)                               OpenSL                              dh(3)



NAME
       dh - Diffie-Hellman key agreement

SYNOPSIS
        #include 
        #include 

        DH *   DHnew(void);
        void   DHfree(DH *dh);

        int    DHsize(const DH *dh);

        DH *   DHgenerateparameters(int primelen, int generator,
                       void (*callback)(int, int, void *), void *cbarg);
        int    DHcheck(const DH *dh, int *codes);

        int    DHgeneratekey(DH *dh);
        int    DHcomputekey(unsigned char *key, BIGNUM *pubkey, DH *dh);

        void DHsetdefaultmethod(const DHMETHOD *meth);
        const DHMETHOD *DHgetdefaultmethod(void);
        int DHsetmethod(DH *dh, const DHMETHOD *meth);
        DH *DHnewmethod(ENGINE *engine);
        const DHMETHOD *DHOpenSL(void);

        int DHgetexnewindex(long argl, char *argp, int (*newfunc)(),
                    int (*dupfunc)(), void (*freefunc)());
        int DHsetexdata(DH *d, int idx, char *arg);
        char *DHgetexdata(DH *d, int idx);

        DH *   d2iDHparams(DH **a, unsigned char **pp, long length);
        int    i2dDHparams(const DH *a, unsigned char **pp);

        int    DHparamsprintfp(FILE *fp, const DH *x);
        int    DHparamsprint(BIO *bp, const DH *x);

DESCRIPTION
       These functions implement the Diffie-Hellman key agreement protocol.
       The generation of shared DH parameters is described in DHgener-
       ateparameters(3); DHgeneratekey(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 Zp (shared)
               BIGNUM *privkey;       / private DH value x
               BIGNUM *pubkey;        / public DH value g^x
               / ...
               };
        DH

       Note that DH keys may use non-standard DHMETHOD 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
       dhparam(1), bn(3), dsa(3), err(3), rand(3), rsa(3), engine(3),
       DHsetmethod(3), DHnew(3), DHgetexnewindex(3), DHgenerateparam-
       eters(3), DHcomputekey(3), d2iDHparams(3), RSAprint(3)



0.9.7l                            2002-08-05                             dh(3)