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
SYNOPSIS¶
#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);
DESCRIPTION¶
An
RSA_METHOD specifies the functions that OpenSSL uses for RSA
operations. By modifying the method, alternative implementations such as
hardware accelerators may be used. IMPORTANT: See the NOTES section for
important information about how these RSA API functions are affected by the
use of
ENGINE API calls.
Initially, the default RSA_METHOD is the OpenSSL internal implementation, as
returned by
RSA_PKCS1_SSLeay().
RSA_set_default_method() makes
meth the default method for all RSA
structures created later.
NB: This is true only whilst no ENGINE has
been set as a default for RSA, so this function is no longer recommended.
RSA_get_default_method() returns a pointer to the current default
RSA_METHOD. However, the meaningfulness of this result is dependent on whether
the ENGINE API is being used, so this function is no longer recommended.
RSA_set_method() selects
meth to perform all operations using the
key
rsa. This will replace the RSA_METHOD used by the RSA key and if
the previous method was supplied by an ENGINE, the handle to that ENGINE will
be released during the change. It is possible to have RSA keys that only work
with certain RSA_METHOD implementations (eg. 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().
RSA_flags() returns the
flags that are set for
rsa's
current RSA_METHOD. See the BUGS section.
RSA_new_method() allocates and initializes an RSA structure so that
engine will be used for the RSA operations. If
engine is NULL,
the default ENGINE for RSA operations is used, and if no default ENGINE is
set, the RSA_METHOD controlled by
RSA_set_default_method() is used.
RSA_flags() returns the
flags that are set for
rsa's
current method.
RSA_new_method() allocates and initializes an
RSA structure so
that
method will be used for the RSA operations. If
method is
NULL, the default method is used.
THE RSA_METHOD STRUCTURE¶
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't 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;
RETURN VALUES¶
RSA_PKCS1_SSLeay(),
RSA_PKCS1_null_method(),
RSA_get_default_method() and
RSA_get_method() return pointers to
the respective RSA_METHODs.
RSA_set_default_method() returns no value.
RSA_set_method() returns a pointer to the old RSA_METHOD implementation
that was replaced. However, this return value should probably be ignored
because if it was supplied by an ENGINE, the pointer could be invalidated at
any time if the ENGINE is unloaded (in fact it could be unloaded as a result
of the
RSA_set_method() function releasing its handle to the ENGINE).
For this reason, the return type may be replaced with a
void
declaration in a future release.
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.
NOTES¶
As of version 0.9.7, RSA_METHOD implementations are grouped together with other
algorithmic APIs (eg. DSA_METHOD, EVP_CIPHER, etc) into
ENGINE modules.
If a default ENGINE is specified for RSA functionality using an ENGINE API
function, that will override any RSA defaults set using the RSA API (ie.
RSA_set_default_method()). For this reason, the ENGINE API is the
recommended way to control default implementations for use in RSA and other
cryptographic algorithms.
BUGS¶
The behaviour of
RSA_flags() is a mis-feature 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).
SEE ALSO¶
rsa(3),
RSA_new(3)
HISTORY¶
RSA_new_method() and
RSA_set_default_method() appeared in SSLeay
0.8.
RSA_get_default_method(),
RSA_set_method() and
RSA_get_method() as well as the rsa_sign and rsa_verify components of
RSA_METHOD were added in OpenSSL 0.9.4.
RSA_set_default_openssl_method() and
RSA_get_default_openssl_method() replaced
RSA_set_default_method() and
RSA_get_default_method()
respectively, and
RSA_set_method() and
RSA_new_method() were
altered to use
ENGINEs rather than
RSA_METHODs during
development of the engine version of OpenSSL 0.9.6. For 0.9.7, the handling of
defaults in the ENGINE API 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 ENGINE API now transparently
overrides the behaviour of defaults in the RSA API without requiring changing
these function prototypes.