RSA_SET_METHOD(3) | Library Functions Manual | RSA_SET_METHOD(3)

# 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

library “libcrypto”
`#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.

`RSA_get_default_method`() returns a pointer to the current default method.

`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. 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, 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.

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. The engine argument is ignored and 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

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.

June 8, 2025 | Debian