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.\" ======================================================================== |
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.\" |
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.IX Title "DH_set_method 3" |
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.TH DH_set_method 3 "2016-09-22" "1.0.1u" "OpenSSL" |
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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.\" way too many mistakes in technical documents. |
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.if n .ad l |
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.nh |
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.SH "NAME" |
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DH_set_default_method, DH_get_default_method, |
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DH_set_method, DH_new_method, DH_OpenSSL \- select DH method |
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.SH "SYNOPSIS" |
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.IX Header "SYNOPSIS" |
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.Vb 2 |
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\& #include <openssl/dh.h> |
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\& #include <openssl/engine.h> |
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\& |
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\& void DH_set_default_method(const DH_METHOD *meth); |
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\& |
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\& const DH_METHOD *DH_get_default_method(void); |
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\& |
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\& int DH_set_method(DH *dh, const DH_METHOD *meth); |
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\& |
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\& DH *DH_new_method(ENGINE *engine); |
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\& |
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\& const DH_METHOD *DH_OpenSSL(void); |
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.Ve |
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.SH "DESCRIPTION" |
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.IX Header "DESCRIPTION" |
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A \fB\s-1DH_METHOD\s0\fR specifies the functions that OpenSSL uses for Diffie-Hellman |
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operations. By modifying the method, alternative implementations |
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such as hardware accelerators may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for |
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important information about how these \s-1DH API\s0 functions are affected by the use |
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of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls. |
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.PP |
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Initially, the default \s-1DH_METHOD\s0 is the OpenSSL internal implementation, as |
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returned by \fIDH_OpenSSL()\fR. |
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.PP |
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\&\fIDH_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1DH\s0 |
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structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set |
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as a default for \s-1DH,\s0 so this function is no longer recommended. |
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.PP |
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\&\fIDH_get_default_method()\fR returns a pointer to the current default \s-1DH_METHOD.\s0 |
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However, the meaningfulness of this result is dependent on whether the \s-1ENGINE |
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API\s0 is being used, so this function is no longer recommended. |
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.PP |
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\&\fIDH_set_method()\fR selects \fBmeth\fR to perform all operations using the key \fBdh\fR. |
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This will replace the \s-1DH_METHOD\s0 used by the \s-1DH\s0 key and if the previous method |
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was supplied by an \s-1ENGINE,\s0 the handle to that \s-1ENGINE\s0 will be released during the |
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change. It is possible to have \s-1DH\s0 keys that only work with certain \s-1DH_METHOD\s0 |
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implementations (eg. from an \s-1ENGINE\s0 module that supports embedded |
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hardware-protected keys), and in such cases attempting to change the \s-1DH_METHOD\s0 |
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for the key can have unexpected results. |
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.PP |
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\&\fIDH_new_method()\fR allocates and initializes a \s-1DH\s0 structure so that \fBengine\fR will |
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be used for the \s-1DH\s0 operations. If \fBengine\fR is \s-1NULL,\s0 the default \s-1ENGINE\s0 for \s-1DH\s0 |
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operations is used, and if no default \s-1ENGINE\s0 is set, the \s-1DH_METHOD\s0 controlled by |
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\&\fIDH_set_default_method()\fR is used. |
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.SH "THE DH_METHOD STRUCTURE" |
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.IX Header "THE DH_METHOD STRUCTURE" |
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.Vb 4 |
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\& typedef struct dh_meth_st |
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\& { |
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\& /* name of the implementation */ |
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\& const char *name; |
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\& |
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\& /* generate private and public DH values for key agreement */ |
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\& int (*generate_key)(DH *dh); |
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\& |
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\& /* compute shared secret */ |
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\& int (*compute_key)(unsigned char *key, BIGNUM *pub_key, DH *dh); |
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\& |
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\& /* compute r = a ^ p mod m (May be NULL for some implementations) */ |
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\& int (*bn_mod_exp)(DH *dh, BIGNUM *r, BIGNUM *a, const BIGNUM *p, |
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\& const BIGNUM *m, BN_CTX *ctx, |
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\& BN_MONT_CTX *m_ctx); |
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\& |
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\& /* called at DH_new */ |
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\& int (*init)(DH *dh); |
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\& |
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\& /* called at DH_free */ |
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\& int (*finish)(DH *dh); |
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\& |
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\& int flags; |
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\& |
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\& char *app_data; /* ?? */ |
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\& |
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\& } DH_METHOD; |
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.Ve |
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.SH "RETURN VALUES" |
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.IX Header "RETURN VALUES" |
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\&\fIDH_OpenSSL()\fR and \fIDH_get_default_method()\fR return pointers to the respective |
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\&\fB\s-1DH_METHOD\s0\fRs. |
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.PP |
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\&\fIDH_set_default_method()\fR returns no value. |
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.PP |
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\&\fIDH_set_method()\fR returns non-zero if the provided \fBmeth\fR was successfully set as |
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the method for \fBdh\fR (including unloading the \s-1ENGINE\s0 handle if the previous |
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method was supplied by an \s-1ENGINE\s0). |
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.PP |
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\&\fIDH_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained by |
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\&\fIERR_get_error\fR\|(3) if the allocation fails. Otherwise it |
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returns a pointer to the newly allocated structure. |
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.SH "NOTES" |
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.IX Header "NOTES" |
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As of version 0.9.7, \s-1DH_METHOD\s0 implementations are grouped together with other |
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algorithmic APIs (eg. \s-1RSA_METHOD, EVP_CIPHER,\s0 etc) in \fB\s-1ENGINE\s0\fR modules. If a |
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default \s-1ENGINE\s0 is specified for \s-1DH\s0 functionality using an \s-1ENGINE API\s0 function, |
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that will override any \s-1DH\s0 defaults set using the \s-1DH API \s0(ie. |
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\&\fIDH_set_default_method()\fR). For this reason, the \s-1ENGINE API\s0 is the recommended way |
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to control default implementations for use in \s-1DH\s0 and other cryptographic |
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algorithms. |
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.SH "SEE ALSO" |
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.IX Header "SEE ALSO" |
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\&\fIdh\fR\|(3), \fIDH_new\fR\|(3) |
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.SH "HISTORY" |
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.IX Header "HISTORY" |
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\&\fIDH_set_default_method()\fR, \fIDH_get_default_method()\fR, \fIDH_set_method()\fR, |
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\&\fIDH_new_method()\fR and \fIDH_OpenSSL()\fR were added in OpenSSL 0.9.4. |
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.PP |
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\&\fIDH_set_default_openssl_method()\fR and \fIDH_get_default_openssl_method()\fR replaced |
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\&\fIDH_set_default_method()\fR and \fIDH_get_default_method()\fR respectively, and |
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\&\fIDH_set_method()\fR and \fIDH_new_method()\fR were altered to use \fB\s-1ENGINE\s0\fRs rather than |
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\&\fB\s-1DH_METHOD\s0\fRs during development of the engine version of OpenSSL 0.9.6. For |
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0.9.7, the handling of defaults in the \s-1ENGINE API\s0 was restructured so that this |
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change was reversed, and behaviour of the other functions resembled more closely |
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the previous behaviour. The behaviour of defaults in the \s-1ENGINE API\s0 now |
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transparently overrides the behaviour of defaults in the \s-1DH API\s0 without |
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requiring changing these function prototypes. |
