src/lib/libcrypto/man/RSA_set_method.3

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.Dd $Mdocdate: January 15 2022 $
.Dt RSA_SET_METHOD 3
.Os
.Sh NAME
.Nm RSA_set_default_method ,
.Nm RSA_get_default_method ,
.Nm RSA_set_method ,
.Nm RSA_get_method ,
.Nm RSA_PKCS1_SSLeay ,
.Nm RSA_flags ,
.Nm RSA_new_method
.Nd select RSA method
.Sh SYNOPSIS
.In openssl/rsa.h
.Ft void
.Fo RSA_set_default_method
.Fa "const RSA_METHOD *meth"
.Fc
.Ft const RSA_METHOD *
.Fn RSA_get_default_method void
.Ft int
.Fo RSA_set_method
.Fa "RSA *rsa"
.Fa "const RSA_METHOD *meth"
.Fc
.Ft const RSA_METHOD *
.Fo RSA_get_method
.Fa "const RSA *rsa"
.Fc
.Ft const RSA_METHOD *
.Fn RSA_PKCS1_SSLeay void
.Ft int
.Fo RSA_flags
.Fa "const RSA *rsa"
.Fc
.Ft RSA *
.Fo RSA_new_method
.Fa "ENGINE *engine"
.Fc
.Sh DESCRIPTION
An
.Vt RSA_METHOD
object contains pointers to the functions used for RSA operations.
By default, the internal implementation returned by
.Fn RSA_PKCS1_SSLeay
is used.
By selecting another method, alternative implementations
such as hardware accelerators may be used.
.Pp
.Fn RSA_set_default_method
selects
.Fa meth
as the default method for all
.Vt RSA
structures created later.
If any
.Vt ENGINE
was registered with
.Xr ENGINE_register_RSA 3
that can be successfully initialized, it overrides the default.
.Pp
.Fn RSA_get_default_method
returns a pointer to the current default method,
even if it is actually overridden by an
.Vt ENGINE .
.Pp
.Fn RSA_set_method
selects
.Fa meth
to perform all operations using the key
.Fa rsa .
This replaces the previous
.Vt RSA_METHOD
used by the RSA key, calling the
.Fa finish
function set up with
.Xr RSA_meth_set_finish 3
if any, and if the previous method was supplied by an
.Vt ENGINE ,
.Xr ENGINE_finish 3
is called on it.
If
.Fa meth
contains an
.Fa init
function set up with
.Xr RSA_meth_set_init 3 ,
that function is called just before returning from
.Fn RSA_set_method .
.Pp
It is possible to have RSA keys that only work with certain
.Vt RSA_METHOD
implementations (e.g. from an
.Vt ENGINE
module that supports embedded hardware-protected keys),
and in such cases attempting to change the
.Vt RSA_METHOD
for the key can have unexpected results.
.Pp
.Fn RSA_get_method
returns a pointer to the
.Vt RSA_METHOD
being used by
.Fa rsa .
This method may or may not be supplied by an
.Vt ENGINE
implementation but if it is, the return value can only be guaranteed
to be valid as long as the RSA key itself is valid and does not
have its implementation changed by
.Fn RSA_set_method .
.Pp
The misleadingly named function
.Fn RSA_flags
returns the flags that are set for the current
.Vt RSA_METHOD
of
.Fa rsa .
The flags used by
.Fa rsa
itself can instead be tested with
.Xr RSA_test_flags 3 .
See the
.Sx BUGS
section for more details.
.Pp
.Fn RSA_new_method
allocates and initializes an
.Vt RSA
structure so that
.Fa engine
is used for the RSA operations.
If
.Fa engine
is
.Dv NULL ,
.Xr ENGINE_get_default_RSA 3
is used.
If that returns
.Dv NULL ,
the default method controlled by
.Fn RSA_set_default_method
is used.
.Pp
The initial
.Fa flags
are copied from the
.Vt RSA_METHOD
object used and will not be affected by later changes to that object,
but may be modified by the optional
.Fa init
function which may have been set up with
.Xr RSA_meth_set_init 3
and which is called just before returning from
.Fn RSA_new_method .
.Sh RETURN VALUES
.Fn RSA_PKCS1_SSLeay ,
.Fn RSA_get_default_method ,
and
.Fn RSA_get_method
return pointers to the respective
.Vt RSA_METHOD .
.Pp
.Fn RSA_set_method
returns 1 on success or 0 on failure.
Currently, it cannot fail.
.Pp
.Fn RSA_new_method
returns
.Dv NULL
and sets an error code that can be obtained by
.Xr ERR_get_error 3
if the allocation fails.
Otherwise it returns a pointer to the newly allocated structure.
.Sh SEE ALSO
.Xr ENGINE_get_default_RSA 3 ,
.Xr ENGINE_register_RSA 3 ,
.Xr ENGINE_set_default_RSA 3 ,
.Xr RSA_meth_new 3 ,
.Xr RSA_new 3
.Sh HISTORY
.Fn RSA_set_default_method ,
.Fn RSA_PKCS1_SSLeay ,
and
.Fn RSA_new_method
first appeared in SSLeay 0.8.0.
.Fn RSA_flags
first appeared in SSLeay 0.9.0.
These functions have been available since
.Ox 2.4 .
.Pp
.Fn RSA_get_default_method ,
.Fn RSA_set_method ,
and
.Fn RSA_get_method
as well as the
.Fa rsa_sign
and
.Fa rsa_verify
components of
.Vt RSA_METHOD
first appeared in OpenSSL 0.9.4 and have been available since
.Ox 2.6 .
.Sh BUGS
The behaviour of
.Fn RSA_flags
is a misfeature that is left as-is for now to avoid creating
compatibility problems.
RSA functionality, such as the encryption functions, are controlled by
the
.Fa flags
value in the
.Vt RSA
key itself, not by the
.Fa flags
value in the
.Vt RSA_METHOD
attached to the RSA key (which is what this function returns).
If the flags element of an
.Vt RSA
key is changed, the changes will be honoured by RSA functionality
but will not be reflected in the return value of the
.Fn RSA_flags
function - in effect
.Fn RSA_flags
behaves more like an RSA_default_flags() function, which does not
currently exist.