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136 .TH dh 3 "2015-01-08" "0.9.8zd" "OpenSSL"
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142 dh \- Diffie\-Hellman key agreement
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/dh.h>
147 \& #include <openssl/engine.h>
149 \& DH * DH_new(void);
150 \& void DH_free(DH *dh);
152 \& int DH_size(const DH *dh);
154 \& DH * DH_generate_parameters(int prime_len, int generator,
155 \& void (*callback)(int, int, void *), void *cb_arg);
156 \& int DH_check(const DH *dh, int *codes);
158 \& int DH_generate_key(DH *dh);
159 \& int DH_compute_key(unsigned char *key, BIGNUM *pub_key, DH *dh);
161 \& void DH_set_default_method(const DH_METHOD *meth);
162 \& const DH_METHOD *DH_get_default_method(void);
163 \& int DH_set_method(DH *dh, const DH_METHOD *meth);
164 \& DH *DH_new_method(ENGINE *engine);
165 \& const DH_METHOD *DH_OpenSSL(void);
167 \& int DH_get_ex_new_index(long argl, char *argp, int (*new_func)(),
168 \& int (*dup_func)(), void (*free_func)());
169 \& int DH_set_ex_data(DH *d, int idx, char *arg);
170 \& char *DH_get_ex_data(DH *d, int idx);
172 \& DH * d2i_DHparams(DH **a, unsigned char **pp, long length);
173 \& int i2d_DHparams(const DH *a, unsigned char **pp);
175 \& int DHparams_print_fp(FILE *fp, const DH *x);
176 \& int DHparams_print(BIO *bp, const DH *x);
179 .IX Header "DESCRIPTION"
180 These functions implement the Diffie-Hellman key agreement protocol.
181 The generation of shared \s-1DH\s0 parameters is described in
182 \&\fIDH_generate_parameters\fR\|(3); \fIDH_generate_key\fR\|(3) describes how
183 to perform a key agreement.
185 The \fB\s-1DH\s0\fR structure consists of several \s-1BIGNUM\s0 components.
190 \& BIGNUM *p; // prime number (shared)
191 \& BIGNUM *g; // generator of Z_p (shared)
192 \& BIGNUM *priv_key; // private DH value x
193 \& BIGNUM *pub_key; // public DH value g^x
199 Note that \s-1DH\s0 keys may use non-standard \fB\s-1DH_METHOD\s0\fR implementations,
200 either directly or by the use of \fB\s-1ENGINE\s0\fR modules. In some cases (eg. an
201 \&\s-1ENGINE\s0 providing support for hardware-embedded keys), these \s-1BIGNUM\s0 values
202 will not be used by the implementation or may be used for alternative data
203 storage. For this reason, applications should generally avoid using \s-1DH\s0
204 structure elements directly and instead use \s-1API\s0 functions to query or
207 .IX Header "SEE ALSO"
208 \&\fIdhparam\fR\|(1), \fIbn\fR\|(3), \fIdsa\fR\|(3), \fIerr\fR\|(3),
209 \&\fIrand\fR\|(3), \fIrsa\fR\|(3), \fIengine\fR\|(3),
210 \&\fIDH_set_method\fR\|(3), \fIDH_new\fR\|(3),
211 \&\fIDH_get_ex_new_index\fR\|(3),
212 \&\fIDH_generate_parameters\fR\|(3),
213 \&\fIDH_compute_key\fR\|(3), \fId2i_DHparams\fR\|(3),
214 \&\fIRSA_print\fR\|(3)