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.\" ========================================================================
.\"
.IX Title "RSA_set_method 3"
.TH RSA_set_method 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
RSA_set_default_method, RSA_get_default_method, RSA_set_method,
RSA_get_method, RSA_PKCS1_SSLeay, RSA_null_method, RSA_flags,
RSA_new_method \- select RSA method
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rsa.h>
\&
\& void RSA_set_default_method(const RSA_METHOD *meth);
\&
\& RSA_METHOD *RSA_get_default_method(void);
\&
\& int RSA_set_method(RSA *rsa, const RSA_METHOD *meth);
\&
\& RSA_METHOD *RSA_get_method(const RSA *rsa);
\&
\& RSA_METHOD *RSA_PKCS1_SSLeay(void);
\&
\& RSA_METHOD *RSA_null_method(void);
\&
\& int RSA_flags(const RSA *rsa);
\&
\& RSA *RSA_new_method(RSA_METHOD *method);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
An \fB\s-1RSA_METHOD\s0\fR specifies the functions that OpenSSL uses for \s-1RSA\s0
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-1RSA API\s0 functions are affected by the
use of \fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
.PP
Initially, the default \s-1RSA_METHOD\s0 is the OpenSSL internal implementation,
as returned by \fBRSA_PKCS1_SSLeay()\fR.
.PP
\&\fBRSA_set_default_method()\fR makes \fBmeth\fR the default method for all \s-1RSA\s0
structures created later. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has
been set as a default for \s-1RSA,\s0 so this function is no longer recommended.
.PP
\&\fBRSA_get_default_method()\fR returns a pointer to the current default
\&\s-1RSA_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.
.PP
\&\fBRSA_set_method()\fR selects \fBmeth\fR to perform all operations using the key
\&\fBrsa\fR. This will replace the \s-1RSA_METHOD\s0 used by the \s-1RSA\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-1RSA\s0 keys that only
work with certain \s-1RSA_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-1RSA_METHOD\s0 for the key can have unexpected
results.
.PP
\&\fBRSA_get_method()\fR returns a pointer to the \s-1RSA_METHOD\s0 being used by \fBrsa\fR.
This method may or may not be supplied by an \s-1ENGINE\s0 implementation, but if
it is, the return value can only be guaranteed to be valid as long as the
\&\s-1RSA\s0 key itself is valid and does not have its implementation changed by
\&\fBRSA_set_method()\fR.
.PP
\&\fBRSA_flags()\fR returns the \fBflags\fR that are set for \fBrsa\fR's current
\&\s-1RSA_METHOD.\s0 See the \s-1BUGS\s0 section.
.PP
\&\fBRSA_new_method()\fR allocates and initializes an \s-1RSA\s0 structure so that
\&\fBengine\fR will be used for the \s-1RSA\s0 operations. If \fBengine\fR is \s-1NULL,\s0 the
default \s-1ENGINE\s0 for \s-1RSA\s0 operations is used, and if no default \s-1ENGINE\s0 is set,
the \s-1RSA_METHOD\s0 controlled by \fBRSA_set_default_method()\fR is used.
.PP
\&\fBRSA_flags()\fR returns the \fBflags\fR that are set for \fBrsa\fR's current method.
.PP
\&\fBRSA_new_method()\fR allocates and initializes an \fB\s-1RSA\s0\fR structure so that
\&\fBmethod\fR will be used for the \s-1RSA\s0 operations. If \fBmethod\fR is \fB\s-1NULL\s0\fR,
the default method is used.
.SH "THE RSA_METHOD STRUCTURE"
.IX Header "THE RSA_METHOD STRUCTURE"
.Vb 4
\& typedef struct rsa_meth_st
\& {
\&     /* name of the implementation */
\&        const char *name;
\&
\&     /* encrypt */
\&        int (*rsa_pub_enc)(int flen, unsigned char *from,
\&          unsigned char *to, RSA *rsa, int padding);
\&
\&     /* verify arbitrary data */
\&        int (*rsa_pub_dec)(int flen, unsigned char *from,
\&          unsigned char *to, RSA *rsa, int padding);
\&
\&     /* sign arbitrary data */
\&        int (*rsa_priv_enc)(int flen, unsigned char *from,
\&          unsigned char *to, RSA *rsa, int padding);
\&
\&     /* decrypt */
\&        int (*rsa_priv_dec)(int flen, unsigned char *from,
\&          unsigned char *to, RSA *rsa, int padding);
\&
\&     /* compute r0 = r0 ^ I mod rsa\->n (May be NULL for some
\&                                        implementations) */
\&        int (*rsa_mod_exp)(BIGNUM *r0, BIGNUM *I, RSA *rsa);
\&
\&     /* compute r = a ^ p mod m (May be NULL for some implementations) */
\&        int (*bn_mod_exp)(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
\&          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
\&
\&     /* called at RSA_new */
\&        int (*init)(RSA *rsa);
\&
\&     /* called at RSA_free */
\&        int (*finish)(RSA *rsa);
\&
\&     /* RSA_FLAG_EXT_PKEY        \- rsa_mod_exp is called for private key
\&      *                            operations, even if p,q,dmp1,dmq1,iqmp
\&      *                            are NULL
\&      * RSA_FLAG_SIGN_VER        \- enable rsa_sign and rsa_verify
\&      * RSA_METHOD_FLAG_NO_CHECK \- don\*(Aqt check pub/private match
\&      */
\&        int flags;
\&
\&        char *app_data; /* ?? */
\&
\&     /* sign. For backward compatibility, this is used only
\&      * if (flags & RSA_FLAG_SIGN_VER)
\&      */
\&        int (*rsa_sign)(int type,
\&                const unsigned char *m, unsigned int m_length,
\&                unsigned char *sigret, unsigned int *siglen, const RSA *rsa);
\&     /* verify. For backward compatibility, this is used only
\&      * if (flags & RSA_FLAG_SIGN_VER)
\&      */
\&        int (*rsa_verify)(int dtype,
\&                const unsigned char *m, unsigned int m_length,
\&                const unsigned char *sigbuf, unsigned int siglen,
\&                                                                const RSA *rsa);
\&     /* keygen. If NULL builtin RSA key generation will be used */
\&        int (*rsa_keygen)(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
\&
\& } RSA_METHOD;
.Ve
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRSA_PKCS1_SSLeay()\fR, \fBRSA_PKCS1_null_method()\fR, \fBRSA_get_default_method()\fR
and \fBRSA_get_method()\fR return pointers to the respective RSA_METHODs.
.PP
\&\fBRSA_set_default_method()\fR returns no value.
.PP
\&\fBRSA_set_method()\fR returns a pointer to the old \s-1RSA_METHOD\s0 implementation
that was replaced. However, this return value should probably be ignored
because if it was supplied by an \s-1ENGINE,\s0 the pointer could be invalidated
at any time if the \s-1ENGINE\s0 is unloaded (in fact it could be unloaded as a
result of the \fBRSA_set_method()\fR function releasing its handle to the
\&\s-1ENGINE\s0). For this reason, the return type may be replaced with a \fBvoid\fR
declaration in a future release.
.PP
\&\fBRSA_new_method()\fR returns \s-1NULL\s0 and sets an error code that can be obtained
by \fBERR_get_error\fR\|(3) if the allocation fails. Otherwise
it returns a pointer to the newly allocated structure.
.SH "NOTES"
.IX Header "NOTES"
As of version 0.9.7, \s-1RSA_METHOD\s0 implementations are grouped together with
other algorithmic APIs (eg. \s-1DSA_METHOD, EVP_CIPHER,\s0 etc) into \fB\s-1ENGINE\s0\fR
modules. If a default \s-1ENGINE\s0 is specified for \s-1RSA\s0 functionality using an
\&\s-1ENGINE API\s0 function, that will override any \s-1RSA\s0 defaults set using the \s-1RSA
API\s0 (ie.  \fBRSA_set_default_method()\fR). For this reason, the \s-1ENGINE API\s0 is the
recommended way to control default implementations for use in \s-1RSA\s0 and other
cryptographic algorithms.
.SH "BUGS"
.IX Header "BUGS"
The behaviour of \fBRSA_flags()\fR is a mis-feature that is left as-is for now
to avoid creating compatibility problems. \s-1RSA\s0 functionality, such as the
encryption functions, are controlled by the \fBflags\fR value in the \s-1RSA\s0 key
itself, not by the \fBflags\fR value in the \s-1RSA_METHOD\s0 attached to the \s-1RSA\s0 key
(which is what this function returns). If the flags element of an \s-1RSA\s0 key
is changed, the changes will be honoured by \s-1RSA\s0 functionality but will not
be reflected in the return value of the \fBRSA_flags()\fR function \- in effect
\&\fBRSA_flags()\fR behaves more like an \fBRSA_default_flags()\fR function (which does
not currently exist).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBrsa\fR\|(3), \fBRSA_new\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fBRSA_new_method()\fR and \fBRSA_set_default_method()\fR appeared in SSLeay 0.8.
\&\fBRSA_get_default_method()\fR, \fBRSA_set_method()\fR and \fBRSA_get_method()\fR as
well as the rsa_sign and rsa_verify components of \s-1RSA_METHOD\s0 were
added in OpenSSL 0.9.4.
.PP
\&\fBRSA_set_default_openssl_method()\fR and \fBRSA_get_default_openssl_method()\fR
replaced \fBRSA_set_default_method()\fR and \fBRSA_get_default_method()\fR
respectively, and \fBRSA_set_method()\fR and \fBRSA_new_method()\fR were altered to use
\&\fB\s-1ENGINE\s0\fRs rather than \fB\s-1RSA_METHOD\s0\fRs 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-1RSA API\s0 without requiring changing these
function prototypes.

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