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Title "dh 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
dh - Diffie-Hellman key agreement Header "SYNOPSIS" .Vb 2 #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); .Ve 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\|(3); DH_generate_key\|(3) describes how to perform a key agreement.

The \s-1DH\s0 structure consists of several \s-1BIGNUM\s0 components.

.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

Note that \s-1DH\s0 keys may use non-standard \s-1DH_METHOD\s0 implementations, either directly or by the use of \s-1ENGINE\s0 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.

Header "SEE ALSO" \fIdhparam\|(1), bn\|(3), dsa\|(3), err\|(3), \fIrand\|(3), rsa\|(3), engine\|(3), \fIDH_set_method\|(3), DH_new\|(3), \fIDH_get_ex_new_index\|(3), \fIDH_generate_parameters\|(3), \fIDH_compute_key\|(3), d2i_DHparams\|(3), \fIRSA_print\|(3)