## NAME

`RSA_set_default_method`

,
`RSA_get_default_method`

,
`RSA_set_method`

,
`RSA_get_method`

,
`RSA_PKCS1_SSLeay`

, `RSA_flags`

,
`RSA_new_method`

—
select RSA method

## SYNOPSIS

```
#include
<openssl/rsa.h>
```

`void`

`RSA_set_default_method`

(`const
RSA_METHOD *meth`);

`const RSA_METHOD *`

`RSA_get_default_method`

(`void`);

`int`

`RSA_set_method`

(`RSA *rsa`,
`const RSA_METHOD *meth`);

`const RSA_METHOD *`

`RSA_get_method`

(`const RSA
*rsa`);

`const RSA_METHOD *`

`RSA_PKCS1_SSLeay`

(`void`);

`int`

`RSA_flags`

(`const RSA *rsa`);

`RSA *`

`RSA_new_method`

(`ENGINE
*engine`);

## DESCRIPTION

An `RSA_METHOD` object contains pointers to
the functions used for RSA operations. By default, the internal
implementation returned by
`RSA_PKCS1_SSLeay`

()
is used. By selecting another method, alternative implementations such as
hardware accelerators may be used.

`RSA_set_default_method`

()
selects `meth` as the default method for all
`RSA` structures created later. If any
`ENGINE` was registered with
ENGINE_register_RSA(3) that can be successfully initialized,
it overrides the default.

`RSA_get_default_method`

()
returns a pointer to the current default method, even if it is actually
overridden by an `ENGINE`.

`RSA_set_method`

()
selects `meth` to perform all operations using the key
`rsa`. This replaces the previous
`RSA_METHOD` used by the RSA key, calling the
`finish` function set up with
RSA_meth_set_finish(3) if any, and if the previous method was
supplied by an `ENGINE`,
ENGINE_finish(3) is called on it. If `meth`
contains an `init` function set up with
RSA_meth_set_init(3), that function is called just before
returning from `RSA_set_method`

().

It is possible to have RSA keys that only work with certain
`RSA_METHOD` implementations (e.g. from an
`ENGINE` module that supports embedded
hardware-protected keys), and in such cases attempting to change the
`RSA_METHOD` for the key can have unexpected
results.

`RSA_get_method`

()
returns a pointer to the `RSA_METHOD` being used by
`rsa`. This method may or may not be supplied by an
`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
`RSA_set_method`

().

The misleadingly named function
`RSA_flags`

()
returns the flags that are set for the current
`RSA_METHOD` of `rsa`. The flags
used by `rsa` itself can instead be tested with
RSA_test_flags(3). See the BUGS
section for more details.

`RSA_new_method`

()
allocates and initializes an `RSA` structure so that
`engine` is used for the RSA operations. If
`engine` is `NULL`

,
ENGINE_get_default_RSA(3) is used. If that returns
`NULL`

, the default method controlled by
`RSA_set_default_method`

() is used.

The initial `flags` are
copied from the `RSA_METHOD` object used and will not be
affected by later changes to that object, but may be modified by the
optional `init` function which may have been set up with
RSA_meth_set_init(3) and which is called just before
returning from
`RSA_new_method`

().

## RETURN VALUES

`RSA_PKCS1_SSLeay`

(),
`RSA_get_default_method`

(), and
`RSA_get_method`

() return pointers to the respective
`RSA_METHOD`.

`RSA_set_method`

() returns 1 on success or 0
on failure. Currently, it cannot fail.

`RSA_new_method`

() returns
`NULL`

and sets an error code that can be obtained by
ERR_get_error(3) if the allocation fails. Otherwise it returns a
pointer to the newly allocated structure.

## SEE ALSO

ENGINE_get_default_RSA(3), ENGINE_register_RSA(3), ENGINE_set_default_RSA(3), RSA_meth_new(3), RSA_new(3)

## HISTORY

`RSA_set_default_method`

(),
`RSA_PKCS1_SSLeay`

(), and
`RSA_new_method`

() first appeared in SSLeay 0.8.0.
`RSA_flags`

() first appeared in SSLeay 0.9.0. These
functions have been available since OpenBSD 2.4.

`RSA_get_default_method`

(),
`RSA_set_method`

(), and
`RSA_get_method`

() as well as the
`rsa_sign` and `rsa_verify`
components of `RSA_METHOD` first appeared in OpenSSL
0.9.4 and have been available since OpenBSD 2.6.

## BUGS

The behaviour of `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 `flags` value in the
`RSA` key itself, not by the `flags`
value in the `RSA_METHOD` attached to the RSA key (which
is what this function returns). If the flags element of an
`RSA` key is changed, the changes will be honoured by
RSA functionality but will not be reflected in the return value of the
`RSA_flags`

() function - in effect
`RSA_flags`

() behaves more like an RSA_default_flags()
function, which does not currently exist.