RSA_METH_NEW(3ossl)

📦

version 3.5.9 · 8 versions

3.5.9 · fedora 43, fedora 44 (latest)
3.5.9 · centos-stream 9
3.5.9 · centos-stream 10
3.5.9 · alpine 3.22
3.5.9 · alpine 3.23, alpine 3.24
3.5.8 · fedora 43
3.5.1 · fedora 43
3.5.5 · fedora 44

💖 NAME 💖

okay so bestie, welcome to RSA_METH_NEW(3ossl) — it's the OpenSSL page all about the routines you use to build up your very own RSA methods. like, custom RSA behavior, but make it yours. 👑

here's the whole squad of functions that live on this page, no cap:

RSA_meth_get0_app_data
RSA_meth_set0_app_data
RSA_meth_new
RSA_meth_free
RSA_meth_dup
RSA_meth_get0_name
RSA_meth_set1_name
RSA_meth_get_flags
RSA_meth_set_flags
RSA_meth_get_pub_enc
RSA_meth_set_pub_enc
RSA_meth_get_pub_dec
RSA_meth_set_pub_dec
RSA_meth_get_priv_enc
RSA_meth_set_priv_enc
RSA_meth_get_priv_dec
RSA_meth_set_priv_dec
RSA_meth_get_mod_exp
RSA_meth_set_mod_exp
RSA_meth_get_bn_mod_exp
RSA_meth_set_bn_mod_exp
RSA_meth_get_init
RSA_meth_set_init
RSA_meth_get_finish
RSA_meth_set_finish
RSA_meth_get_sign
RSA_meth_set_sign
RSA_meth_get_verify
RSA_meth_set_verify
RSA_meth_get_keygen
RSA_meth_set_keygen
RSA_meth_get_multi_prime_keygen
RSA_meth_set_multi_prime_keygen

✨ SYNOPSIS ✨

first thing's first, you gotta pull in the header, periodt:

#include <openssl/rsa.h>

🫶 heads up bestie, this is important: the functions below have been deprecated since OpenSSL 3.0. you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value — peep openssl_user_macros(7) for the deets. 💀

and here's the full lineup, verbatim, no edits, i promise:

RSA_METHOD *RSA_meth_new(const char *name, int flags);
void RSA_meth_free(RSA_METHOD *meth);

RSA_METHOD *RSA_meth_dup(const RSA_METHOD *meth);

const char *RSA_meth_get0_name(const RSA_METHOD *meth);
int RSA_meth_set1_name(RSA_METHOD *meth, const char *name);

int RSA_meth_get_flags(const RSA_METHOD *meth);
int RSA_meth_set_flags(RSA_METHOD *meth, int flags);

void *RSA_meth_get0_app_data(const RSA_METHOD *meth);
int RSA_meth_set0_app_data(RSA_METHOD *meth, void *app_data);

int (*RSA_meth_get_pub_enc(const RSA_METHOD *meth))(int flen, const unsigned char *from,
                                                    unsigned char *to, RSA *rsa, int padding);
int RSA_meth_set_pub_enc(RSA_METHOD *rsa,
                         int (*pub_enc)(int flen, const unsigned char *from,
                                        unsigned char *to, RSA *rsa,
                                        int padding));

int (*RSA_meth_get_pub_dec(const RSA_METHOD *meth))
    (int flen, const unsigned char *from,
     unsigned char *to, RSA *rsa, int padding);
int RSA_meth_set_pub_dec(RSA_METHOD *rsa,
                         int (*pub_dec)(int flen, const unsigned char *from,
                                        unsigned char *to, RSA *rsa,
                                        int padding));

int (*RSA_meth_get_priv_enc(const RSA_METHOD *meth))(int flen, const unsigned char *from,
                                                     unsigned char *to, RSA *rsa,
                                                     int padding);
int RSA_meth_set_priv_enc(RSA_METHOD *rsa,
                          int (*priv_enc)(int flen, const unsigned char *from,
                                          unsigned char *to, RSA *rsa, int padding));

int (*RSA_meth_get_priv_dec(const RSA_METHOD *meth))(int flen, const unsigned char *from,
                                                     unsigned char *to, RSA *rsa,
                                                     int padding);
int RSA_meth_set_priv_dec(RSA_METHOD *rsa,
                          int (*priv_dec)(int flen, const unsigned char *from,
                                          unsigned char *to, RSA *rsa, int padding));

/* Can be null */
int (*RSA_meth_get_mod_exp(const RSA_METHOD *meth))(BIGNUM *r0, const BIGNUM *i,
                                                    RSA *rsa, BN_CTX *ctx);
int RSA_meth_set_mod_exp(RSA_METHOD *rsa,
                         int (*mod_exp)(BIGNUM *r0, const BIGNUM *i, RSA *rsa,
                                        BN_CTX *ctx));

/* Can be null */
int (*RSA_meth_get_bn_mod_exp(const RSA_METHOD *meth))(BIGNUM *r, const BIGNUM *a,
                                                       const BIGNUM *p, const BIGNUM *m,
                                                       BN_CTX *ctx, BN_MONT_CTX *m_ctx);
int RSA_meth_set_bn_mod_exp(RSA_METHOD *rsa,
                            int (*bn_mod_exp)(BIGNUM *r, const BIGNUM *a,
                                              const BIGNUM *p, const BIGNUM *m,
                                              BN_CTX *ctx, BN_MONT_CTX *m_ctx));

/* called at new */
int (*RSA_meth_get_init(const RSA_METHOD *meth) (RSA *rsa);
int RSA_meth_set_init(RSA_METHOD *rsa, int (*init (RSA *rsa));

/* called at free */
int (*RSA_meth_get_finish(const RSA_METHOD *meth))(RSA *rsa);
int RSA_meth_set_finish(RSA_METHOD *rsa, int (*finish)(RSA *rsa));

int (*RSA_meth_get_sign(const RSA_METHOD *meth))(int type, const unsigned char *m,
                                                 unsigned int m_length,
                                                 unsigned char *sigret,
                                                 unsigned int *siglen, const RSA *rsa);
int RSA_meth_set_sign(RSA_METHOD *rsa,
                      int (*sign)(int type, const unsigned char *m,
                                  unsigned int m_length, unsigned char *sigret,
                                  unsigned int *siglen, const RSA *rsa));

int (*RSA_meth_get_verify(const RSA_METHOD *meth))(int dtype, const unsigned char *m,
                                                   unsigned int m_length,
                                                   const unsigned char *sigbuf,
                                                   unsigned int siglen, const RSA *rsa);
int RSA_meth_set_verify(RSA_METHOD *rsa,
                        int (*verify)(int dtype, const unsigned char *m,
                                      unsigned int m_length,
                                      const unsigned char *sigbuf,
                                      unsigned int siglen, const RSA *rsa));

int (*RSA_meth_get_keygen(const RSA_METHOD *meth))(RSA *rsa, int bits, BIGNUM *e,
                                                   BN_GENCB *cb);
int RSA_meth_set_keygen(RSA_METHOD *rsa,
                        int (*keygen)(RSA *rsa, int bits, BIGNUM *e,
                                      BN_GENCB *cb));

int (*RSA_meth_get_multi_prime_keygen(const RSA_METHOD *meth))(RSA *rsa, int bits,
                                                               int primes, BIGNUM *e,
                                                               BN_GENCB *cb);

int RSA_meth_set_multi_prime_keygen(RSA_METHOD *meth,
                                    int (*keygen) (RSA *rsa, int bits,
                                                   int primes, BIGNUM *e,
                                                   BN_GENCB *cb));

lowkey that's a lot of function pointers and we are so here for it 💅

✨ DESCRIPTION ✨

🚨 DEPRECATION ALERT, BESTIE 🚨 Okay so first things first: every single function on this page is deprecated. 💀 Like, all of them. Applications should instead use the OSSL_PROVIDER APIs. No cap. If you're writing new code, this is not the move. Periodt. ✨

The RSA_METHOD type is a structure used for the provision of custom RSA implementations. It gives OpenSSL a whole set of functions for implementing the various RSA capabilities. It's giving plug-in energy, but make it cryptography. 🔐

RSA_meth_new() — creates a brand new RSA_METHOD structure. You give it a unique name and a set of flags. The name should be a NULL terminated string. It gets duplicated and stored in the RSA_METHOD object. It is the caller's responsibility to free the original string. The flags get used during the construction of a new RSA object based on this RSA_METHOD. Any new RSA object will have those flags set by default. 💅
RSA_meth_dup() — creates a duplicate copy of the RSA_METHOD object you pass as a parameter. This might be useful for creating a new RSA_METHOD based on an existing one, but with some differences. Lowkey a glow-up but for structs. 🦋
RSA_meth_free() — destroys an RSA_METHOD structure and frees up any memory associated with it. If the argument is NULL, nothing is done. No thoughts, just free. 🧚
RSA_meth_get0_name() — will return a pointer to the name of this RSA_METHOD. This is a pointer to the internal name string and so should not be freed by the caller. RSA_meth_set1_name() sets the name of the RSA_METHOD to name. The string is duplicated and the copy is stored in the RSA_METHOD structure, so the caller remains responsible for freeing the memory associated with name. Don't double-free, bestie. 😭
RSA_meth_get_flags() — returns the current value of the flags associated with this RSA_METHOD. RSA_meth_set_flags() provides the ability to set these flags. Flags are the vibe check of your method. 🌈
RSA_meth_get0_app_data() and RSA_meth_set0_app_data() — provide the ability to associate implementation specific data with the RSA_METHOD. It is the application's responsibility to free this data before the RSA_METHOD is freed via a call to RSA_meth_free(). So like, clean up your own mess. 🫶
RSA_meth_get_sign() and RSA_meth_set_sign() — get and set the function used for creating an RSA signature respectively. This function will be called in response to the application calling RSA_sign(). The parameters for the function have the same meaning as for RSA_sign(). Sign it, sign it. ✍️
RSA_meth_get_verify() and RSA_meth_set_verify() — get and set the function used for verifying an RSA signature respectively. This function will be called in response to the application calling RSA_verify(). The parameters for the function have the same meaning as for RSA_verify(). Verify before you trust. 👑
RSA_meth_get_mod_exp() and RSA_meth_set_mod_exp() — get and set the function used for CRT computations. CRT is giving math class but make it fast. ⚡
RSA_meth_get_bn_mod_exp() and RSA_meth_set_bn_mod_exp() — get and set the function used for CRT computations, specifically the following value:

r = a ^ p mod m

Both the mod_exp() and bn_mod_exp() functions are called by the default OpenSSL method during encryption, decryption, signing and verification. So yeah, they pull up everywhere. 🔥

RSA_meth_get_init() and RSA_meth_set_init() — get and set the function used for creating a new RSA instance respectively. This function will be called in response to the application calling RSA_new() (if the current default RSA_METHOD is this one) or RSA_new_method(). The RSA_new() and RSA_new_method() functions will allocate the memory for the new RSA object, and a pointer to this newly allocated structure will be passed as a parameter to the function. This function may be NULL. So it's optional, but iconic when present. 🎀
RSA_meth_get_finish() and RSA_meth_set_finish() — get and set the function used for destroying an instance of an RSA object respectively. This function will be called in response to the application calling RSA_free(). A pointer to the RSA to be destroyed is passed as a parameter. The destroy function should be used for RSA implementation specific clean up. The memory for the RSA itself should not be freed by this function. This function may be NULL. Do NOT free the RSA itself here, okay? That's a different function's job. 💀
RSA_meth_get_keygen() and RSA_meth_set_keygen() — get and set the function used for generating a new RSA key pair respectively. This function will be called in response to the application calling RSA_generate_key_ex(). The parameter for the function has the same meaning as for RSA_generate_key_ex(). Keygen is the main character moment. 🔑
RSA_meth_get_multi_prime_keygen() and RSA_meth_set_multi_prime_keygen() — get and set the function used for generating a new multi-prime RSA key pair respectively. This function will be called in response to the application calling RSA_generate_multi_prime_key(). The parameter for the function has the same meaning as for RSA_generate_multi_prime_key(). Multi-prime? More primes, more problems, more slay. 💅
RSA_meth_get_pub_enc(), RSA_meth_set_pub_enc(), RSA_meth_get_pub_dec(), RSA_meth_set_pub_dec(), RSA_meth_get_priv_enc(), RSA_meth_set_priv_enc(), RSA_meth_get_priv_dec(), RSA_meth_set_priv_dec() — get and set the functions used for public and private key encryption and decryption. These functions will be called in response to the application calling RSA_public_encrypt(), RSA_private_decrypt(), RSA_private_encrypt() and RSA_public_decrypt() and take the same parameters as those. So many functions, but they all ate. 🍓

💖 RETURN VALUES 💖

RSA_meth_new() and RSA_meth_dup() return the newly allocated RSA_METHOD object or NULL on failure. So if you get NULL, it's not giving. 😭
RSA_meth_get0_name() and RSA_meth_get_flags() return the name and flags associated with the RSA_METHOD respectively. Cute and simple. ✨
All other RSA_meth_get_*() functions return the appropriate function pointer that has been set in the RSA_METHOD, or NULL if no such pointer has yet been set. If it's NULL, it's not set yet, bestie. 🙈
RSA_meth_set1_name and all RSA_meth_set_*() functions return 1 on success or 0 on failure. So 1 is slay, 0 is not. 👑

👀 SEE ALSO 👀

📜 HISTORY 📜

All of these functions were deprecated in OpenSSL 3.0. 💀
RSA_meth_get_multi_prime_keygen() and RSA_meth_set_multi_prime_keygen() were added in OpenSSL 1.1.1. 🦋
Other functions described here were added in OpenSSL 1.1.0. ✨

⚖️ COPYRIGHT ⚖️

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

That's the whole vibe, bestie 💖. This page is from OpenSSL 3.5.9, dated 2026-09-29, and it's the RSA_METH_NEW(3ossl) manual page. Periodt. ✨

📦 where this page comes from

fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-14: a language model's rewrite of the original, under its terms