OpenGrok

DH_set_method.3 revision 1.1

$NetBSD: DH_set_method.3,v 1.1 2018/02/03 22:43:38 christos Exp $

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Title "DH_set_method 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
.nh DH_set_default_method, DH_get_default_method, DH_set_method, DH_new_method, DH_OpenSSL - select DH method libcrypto, -lcrypto Header "SYNOPSIS" .Vb 2 #include <openssl/dh.h> #include <openssl/engine.h> \& 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); .Ve Header "DESCRIPTION" A \s-1DH_METHOD\s0 specifies the functions that OpenSSL uses for Diffie-Hellman operations. By modifying the method, alternative implementations such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for important information about how these \s-1DH API\s0 functions are affected by the use of \s-1ENGINE\s0 \s-1API\s0 calls.

Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as returned by DH_OpenSSL().

\fIDH_set_default_method() makes meth the default method for all \s-1DH\s0 structures created later. \s-1NB\s0: This is true only whilst no \s-1ENGINE\s0 has been set as a default for \s-1DH,\s0 so this function is no longer recommended.

\fIDH_get_default_method() returns a pointer to the current default \s-1DH_METHOD.\s0 However, the meaningfulness of this result is dependent on whether the \s-1ENGINE API\s0 is being used, so this function is no longer recommended.

\fIDH_set_method() selects meth to perform all operations using the key dh. This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method was supplied by an \s-1ENGINE,\s0 the handle to that \s-1ENGINE\s0 will be released during the change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0 implementations (eg. from an \s-1ENGINE\s0 module that supports embedded hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0 for the key can have unexpected results.

\fIDH_new_method() allocates and initializes a \s-1DH\s0 structure so that engine will be used for the \s-1DH\s0 operations. If engine is \s-1NULL,\s0 the default \s-1ENGINE\s0 for \s-1DH\s0 operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by \fIDH_set_default_method() is used.

Header "THE DH_METHOD STRUCTURE" .Vb 4 typedef struct dh_meth_st { /* name of the implementation */ const char *name; \& /* generate private and public DH values for key agreement */ int (*generate_key)(DH *dh); \& /* compute shared secret */ int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); \& /* compute r = a ^ p mod m (May be NULL for some implementations) */ int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx); \& /* called at DH_new */ int (*init)(DH *dh); \& /* called at DH_free */ int (*finish)(DH *dh); \& int flags; \& char *app_data; /* ?? */ \& } DH_METHOD; .Ve Header "RETURN VALUES" \fIDH_OpenSSL() and DH_get_default_method() return pointers to the respective \fB\s-1DH_METHOD\s0s.

\fIDH_set_default_method() returns no value.

\fIDH_set_method() returns non-zero if the provided meth was successfully set as the method for dh (including unloading the \s-1ENGINE\s0 handle if the previous method was supplied by an \s-1ENGINE\s0).

\fIDH_new_method() returns \s-1NULL\s0 and sets an error code that can be obtained by \fIERR_get_error\|(3) if the allocation fails. Otherwise it returns a pointer to the newly allocated structure.

Header "NOTES" As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other algorithmic APIs (eg. \s-1RSA_METHOD, EVP_CIPHER,\s0 etc) in \s-1ENGINE\s0 modules. If a default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE API\s0 function, that will override any \s-1DH\s0 defaults set using the \s-1DH API \s0(ie. \fIDH_set_default_method()). For this reason, the \s-1ENGINE API\s0 is the recommended way to control default implementations for use in \s-1DH\s0 and other cryptographic algorithms. Header "SEE ALSO" \fIopenssl_dh\|(3), DH_new\|(3) Header "HISTORY" \fIDH_set_default_method(), DH_get_default_method(), DH_set_method(), \fIDH_new_method() and DH_OpenSSL() were added in OpenSSL 0.9.4.

\fIDH_set_default_openssl_method() and DH_get_default_openssl_method() replaced \fIDH_set_default_method() and DH_get_default_method() respectively, and \fIDH_set_method() and DH_new_method() were altered to use \s-1ENGINE\s0s rather than \fB\s-1DH_METHOD\s0s during development of the engine version of OpenSSL 0.9.6. For 0.9.7, the handling of defaults in the \s-1ENGINE API\s0 was restructured so that this change was reversed, and behaviour of the other functions resembled more closely the previous behaviour. The behaviour of defaults in the \s-1ENGINE API\s0 now transparently overrides the behaviour of defaults in the \s-1DH API\s0 without requiring changing these function prototypes.

Indexes created Fri Apr 24 00:22:58 UTC 2026