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143 lines
5.2 KiB
143 lines
5.2 KiB
=pod |
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=head1 NAME |
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DSA_set_default_method, DSA_get_default_method, |
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DSA_set_method, DSA_new_method, DSA_OpenSSL - select DSA method |
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=head1 SYNOPSIS |
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#include <openssl/dsa.h> |
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#include <openssl/engine.h> |
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void DSA_set_default_method(const DSA_METHOD *meth); |
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const DSA_METHOD *DSA_get_default_method(void); |
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int DSA_set_method(DSA *dsa, const DSA_METHOD *meth); |
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DSA *DSA_new_method(ENGINE *engine); |
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DSA_METHOD *DSA_OpenSSL(void); |
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=head1 DESCRIPTION |
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A B<DSA_METHOD> specifies the functions that OpenSSL uses for DSA |
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operations. By modifying the method, alternative implementations |
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such as hardware accelerators may be used. IMPORTANT: See the NOTES section for |
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important information about how these DSA API functions are affected by the use |
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of B<ENGINE> API calls. |
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Initially, the default DSA_METHOD is the OpenSSL internal implementation, |
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as returned by DSA_OpenSSL(). |
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DSA_set_default_method() makes B<meth> the default method for all DSA |
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structures created later. B<NB>: This is true only whilst no ENGINE has |
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been set as a default for DSA, so this function is no longer recommended. |
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DSA_get_default_method() returns a pointer to the current default |
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DSA_METHOD. However, the meaningfulness of this result is dependent on |
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whether the ENGINE API is being used, so this function is no longer |
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recommended. |
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DSA_set_method() selects B<meth> to perform all operations using the key |
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B<rsa>. This will replace the DSA_METHOD used by the DSA key and if the |
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previous method was supplied by an ENGINE, the handle to that ENGINE will |
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be released during the change. It is possible to have DSA keys that only |
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work with certain DSA_METHOD implementations (eg. from an ENGINE module |
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that supports embedded hardware-protected keys), and in such cases |
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attempting to change the DSA_METHOD for the key can have unexpected |
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results. |
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DSA_new_method() allocates and initializes a DSA structure so that B<engine> |
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will be used for the DSA operations. If B<engine> is NULL, the default engine |
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for DSA operations is used, and if no default ENGINE is set, the DSA_METHOD |
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controlled by DSA_set_default_method() is used. |
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=head1 THE DSA_METHOD STRUCTURE |
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struct |
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{ |
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/* name of the implementation */ |
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const char *name; |
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/* sign */ |
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DSA_SIG *(*dsa_do_sign)(const unsigned char *dgst, int dlen, |
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DSA *dsa); |
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/* pre-compute k^-1 and r */ |
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int (*dsa_sign_setup)(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp, |
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BIGNUM **rp); |
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/* verify */ |
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int (*dsa_do_verify)(const unsigned char *dgst, int dgst_len, |
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DSA_SIG *sig, DSA *dsa); |
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/* compute rr = a1^p1 * a2^p2 mod m (May be NULL for some |
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implementations) */ |
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int (*dsa_mod_exp)(DSA *dsa, BIGNUM *rr, BIGNUM *a1, BIGNUM *p1, |
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BIGNUM *a2, BIGNUM *p2, BIGNUM *m, |
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BN_CTX *ctx, BN_MONT_CTX *in_mont); |
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/* compute r = a ^ p mod m (May be NULL for some implementations) */ |
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int (*bn_mod_exp)(DSA *dsa, BIGNUM *r, BIGNUM *a, |
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const BIGNUM *p, const BIGNUM *m, |
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BN_CTX *ctx, BN_MONT_CTX *m_ctx); |
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/* called at DSA_new */ |
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int (*init)(DSA *DSA); |
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/* called at DSA_free */ |
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int (*finish)(DSA *DSA); |
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int flags; |
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char *app_data; /* ?? */ |
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} DSA_METHOD; |
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=head1 RETURN VALUES |
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DSA_OpenSSL() and DSA_get_default_method() return pointers to the respective |
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B<DSA_METHOD>s. |
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DSA_set_default_method() returns no value. |
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DSA_set_method() returns non-zero if the provided B<meth> was successfully set as |
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the method for B<dsa> (including unloading the ENGINE handle if the previous |
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method was supplied by an ENGINE). |
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DSA_new_method() returns NULL and sets an error code that can be |
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obtained by L<ERR_get_error(3)|ERR_get_error(3)> if the allocation |
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fails. Otherwise it returns a pointer to the newly allocated structure. |
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=head1 NOTES |
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As of version 0.9.7, DSA_METHOD implementations are grouped together with other |
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algorithmic APIs (eg. RSA_METHOD, EVP_CIPHER, etc) in B<ENGINE> modules. If a |
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default ENGINE is specified for DSA functionality using an ENGINE API function, |
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that will override any DSA defaults set using the DSA API (ie. |
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DSA_set_default_method()). For this reason, the ENGINE API is the recommended way |
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to control default implementations for use in DSA and other cryptographic |
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algorithms. |
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=head1 SEE ALSO |
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L<dsa(3)|dsa(3)>, L<DSA_new(3)|DSA_new(3)> |
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=head1 HISTORY |
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DSA_set_default_method(), DSA_get_default_method(), DSA_set_method(), |
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DSA_new_method() and DSA_OpenSSL() were added in OpenSSL 0.9.4. |
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DSA_set_default_openssl_method() and DSA_get_default_openssl_method() replaced |
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DSA_set_default_method() and DSA_get_default_method() respectively, and |
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DSA_set_method() and DSA_new_method() were altered to use B<ENGINE>s rather than |
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B<DSA_METHOD>s 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 ENGINE API 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 ENGINE API now |
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transparently overrides the behaviour of defaults in the DSA API without |
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requiring changing these function prototypes. |
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=cut
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