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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" dh \- Diffie\-Hellman key agreement .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 2 \& #include \& #include \& \& 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); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" These functions implement the Diffie-Hellman key agreement protocol. The generation of shared \s-1DH\s0 parameters is described in \&\fIDH_generate_parameters\fR\|(3); \fIDH_generate_key\fR\|(3) describes how to perform a key agreement. .PP The \fB\s-1DH\s0\fR structure consists of several \s-1BIGNUM\s0 components. .PP .Vb 9 \& 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 .Ve .PP Note that \s-1DH\s0 keys may use non-standard \fB\s-1DH_METHOD\s0\fR implementations, either directly or by the use of \fB\s-1ENGINE\s0\fR modules. In some cases (eg. an \&\s-1ENGINE\s0 providing support for hardware-embedded keys), these \s-1BIGNUM\s0 values will not be used by the implementation or may be used for alternative data storage. For this reason, applications should generally avoid using \s-1DH\s0 structure elements directly and instead use \s-1API\s0 functions to query or modify keys. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIdhparam\fR\|(1), \fIbn\fR\|(3), \fIdsa\fR\|(3), \fIerr\fR\|(3), \&\fIrand\fR\|(3), \fIrsa\fR\|(3), \fIengine\fR\|(3), \&\fIDH_set_method\fR\|(3), \fIDH_new\fR\|(3), \&\fIDH_get_ex_new_index\fR\|(3), \&\fIDH_generate_parameters\fR\|(3), \&\fIDH_compute_key\fR\|(3), \fId2i_DHparams\fR\|(3), \&\fIRSA_print\fR\|(3)