1RSA_SET_METHOD(3)                   OpenSSL                  RSA_SET_METHOD(3)
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NAME

6       RSA_set_default_method, RSA_get_default_method, RSA_set_method,
7       RSA_get_method, RSA_PKCS1_OpenSSL, RSA_flags, RSA_new_method - select
8       RSA method
9

SYNOPSIS

11        #include <openssl/rsa.h>
12
13        void RSA_set_default_method(const RSA_METHOD *meth);
14
15        RSA_METHOD *RSA_get_default_method(void);
16
17        int RSA_set_method(RSA *rsa, const RSA_METHOD *meth);
18
19        RSA_METHOD *RSA_get_method(const RSA *rsa);
20
21        RSA_METHOD *RSA_PKCS1_OpenSSL(void);
22
23        int RSA_flags(const RSA *rsa);
24
25        RSA *RSA_new_method(ENGINE *engine);
26

DESCRIPTION

28       An RSA_METHOD specifies the functions that OpenSSL uses for RSA
29       operations. By modifying the method, alternative implementations such
30       as hardware accelerators may be used. IMPORTANT: See the NOTES section
31       for important information about how these RSA API functions are
32       affected by the use of ENGINE API calls.
33
34       Initially, the default RSA_METHOD is the OpenSSL internal
35       implementation, as returned by RSA_PKCS1_OpenSSL().
36
37       RSA_set_default_method() makes meth the default method for all RSA
38       structures created later.  NB: This is true only whilst no ENGINE has
39       been set as a default for RSA, so this function is no longer
40       recommended.  This function is not thread-safe and should not be called
41       at the same time as other OpenSSL functions.
42
43       RSA_get_default_method() returns a pointer to the current default
44       RSA_METHOD. However, the meaningfulness of this result is dependent on
45       whether the ENGINE API is being used, so this function is no longer
46       recommended.
47
48       RSA_set_method() selects meth to perform all operations using the key
49       rsa. This will replace the RSA_METHOD used by the RSA key and if the
50       previous method was supplied by an ENGINE, the handle to that ENGINE
51       will be released during the change. It is possible to have RSA keys
52       that only work with certain RSA_METHOD implementations (e.g. from an
53       ENGINE module that supports embedded hardware-protected keys), and in
54       such cases attempting to change the RSA_METHOD for the key can have
55       unexpected results.
56
57       RSA_get_method() returns a pointer to the RSA_METHOD being used by rsa.
58       This method may or may not be supplied by an ENGINE implementation, but
59       if it is, the return value can only be guaranteed to be valid as long
60       as the RSA key itself is valid and does not have its implementation
61       changed by RSA_set_method().
62
63       RSA_flags() returns the flags that are set for rsa's current
64       RSA_METHOD. See the BUGS section.
65
66       RSA_new_method() allocates and initializes an RSA structure so that
67       engine will be used for the RSA operations. If engine is NULL, the
68       default ENGINE for RSA operations is used, and if no default ENGINE is
69       set, the RSA_METHOD controlled by RSA_set_default_method() is used.
70
71       RSA_flags() returns the flags that are set for rsa's current method.
72
73       RSA_new_method() allocates and initializes an RSA structure so that
74       method will be used for the RSA operations. If method is NULL, the
75       default method is used.
76

THE RSA_METHOD STRUCTURE

78        typedef struct rsa_meth_st
79        {
80            /* name of the implementation */
81            const char *name;
82
83            /* encrypt */
84            int (*rsa_pub_enc)(int flen, unsigned char *from,
85                               unsigned char *to, RSA *rsa, int padding);
86
87            /* verify arbitrary data */
88            int (*rsa_pub_dec)(int flen, unsigned char *from,
89                               unsigned char *to, RSA *rsa, int padding);
90
91            /* sign arbitrary data */
92            int (*rsa_priv_enc)(int flen, unsigned char *from,
93                                unsigned char *to, RSA *rsa, int padding);
94
95            /* decrypt */
96            int (*rsa_priv_dec)(int flen, unsigned char *from,
97                                unsigned char *to, RSA *rsa, int padding);
98
99            /* compute r0 = r0 ^ I mod rsa->n (May be NULL for some implementations) */
100            int (*rsa_mod_exp)(BIGNUM *r0, BIGNUM *I, RSA *rsa);
101
102            /* compute r = a ^ p mod m (May be NULL for some implementations) */
103            int (*bn_mod_exp)(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
104                              const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
105
106            /* called at RSA_new */
107            int (*init)(RSA *rsa);
108
109            /* called at RSA_free */
110            int (*finish)(RSA *rsa);
111
112            /*
113             * RSA_FLAG_EXT_PKEY        - rsa_mod_exp is called for private key
114             *                            operations, even if p,q,dmp1,dmq1,iqmp
115             *                            are NULL
116             * RSA_METHOD_FLAG_NO_CHECK - don't check pub/private match
117             */
118            int flags;
119
120            char *app_data; /* ?? */
121
122            int (*rsa_sign)(int type,
123                            const unsigned char *m, unsigned int m_length,
124                            unsigned char *sigret, unsigned int *siglen, const RSA *rsa);
125            int (*rsa_verify)(int dtype,
126                              const unsigned char *m, unsigned int m_length,
127                              const unsigned char *sigbuf, unsigned int siglen,
128                              const RSA *rsa);
129            /* keygen. If NULL builtin RSA key generation will be used */
130            int (*rsa_keygen)(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
131
132        } RSA_METHOD;
133

RETURN VALUES

135       RSA_PKCS1_OpenSSL(), RSA_PKCS1_null_method(), RSA_get_default_method()
136       and RSA_get_method() return pointers to the respective RSA_METHODs.
137
138       RSA_set_default_method() returns no value.
139
140       RSA_set_method() returns a pointer to the old RSA_METHOD implementation
141       that was replaced. However, this return value should probably be
142       ignored because if it was supplied by an ENGINE, the pointer could be
143       invalidated at any time if the ENGINE is unloaded (in fact it could be
144       unloaded as a result of the RSA_set_method() function releasing its
145       handle to the ENGINE). For this reason, the return type may be replaced
146       with a void declaration in a future release.
147
148       RSA_new_method() returns NULL and sets an error code that can be
149       obtained by ERR_get_error(3) if the allocation fails. Otherwise it
150       returns a pointer to the newly allocated structure.
151

BUGS

153       The behaviour of RSA_flags() is a mis-feature that is left as-is for
154       now to avoid creating compatibility problems. RSA functionality, such
155       as the encryption functions, are controlled by the flags value in the
156       RSA key itself, not by the flags value in the RSA_METHOD attached to
157       the RSA key (which is what this function returns). If the flags element
158       of an RSA key is changed, the changes will be honoured by RSA
159       functionality but will not be reflected in the return value of the
160       RSA_flags() function - in effect RSA_flags() behaves more like an
161       RSA_default_flags() function (which does not currently exist).
162

SEE ALSO

164       RSA_new(3)
165

HISTORY

167       The RSA_null_method(), which was a partial attempt to avoid patent
168       issues, was replaced to always return NULL in OpenSSL 1.1.1.
169
171       Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
172
173       Licensed under the OpenSSL license (the "License").  You may not use
174       this file except in compliance with the License.  You can obtain a copy
175       in the file LICENSE in the source distribution or at
176       <https://www.openssl.org/source/license.html>.
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1801.1.1q                            2022-07-21                 RSA_SET_METHOD(3)
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