RSA_private_encrypt, RSA_public_decrypt - low-level signature operations

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       Licensed  under  the  Apache License 2.0 (the "License").  You may not use this file except in compliance
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       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                          RSA_PRIVATE_ENCRYPT(3SSL)

       Both of the functions described on this page are deprecated.  Applications should instead use
       EVP_PKEY_sign_init_ex(3), EVP_PKEY_sign(3), EVP_PKEY_verify_recover_init(3), and
       EVP_PKEY_verify_recover(3).

       These functions handle RSA signatures at a low-level.

       RSA_private_encrypt() signs the flen bytes at from (usually a message digest with an algorithm
       identifier) using the private key rsa and stores the signature in to. to must point to RSA_size(rsa)
       bytes of memory.

       padding denotes one of the following modes:

       RSA_PKCS1_PADDING
           PKCS  #1  v1.5  padding.  This function does not handle the algorithmIdentifier specified in PKCS #1.
           When generating or verifying PKCS #1 signatures, RSA_sign(3) and RSA_verify(3) should be used.

       RSA_NO_PADDING
           Raw RSA signature. This mode should only be used to implement cryptographically sound  padding  modes
           in the application code.  Signing user data directly with RSA is insecure.

       RSA_public_decrypt()  recovers  the  message  digest from the flen bytes long signature at from using the
       signer's public key rsa. to must point to a memory section large enough to hold the message digest (which
       is smaller than RSA_size(rsa)-11). padding is the padding mode that was used to sign the data.

       Both of these functions were deprecated in OpenSSL 3.0.

       RSA_private_encrypt, RSA_public_decrypt - low-level signature operations

RSA_private_encrypt() returns the size  of  the  signature  (i.e.,  RSA_size(rsa)).  RSA_public_decrypt()
       returns the size of the recovered message digest.

       On error, -1 is returned; the error codes can be obtained by ERR_get_error(3).

ERR_get_error(3), RSA_sign(3), RSA_verify(3), EVP_PKEY_sign(3), EVP_PKEY_verify_recover(3)

        #include <openssl/rsa.h>

       The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining
       OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

        int RSA_private_encrypt(int flen, unsigned char *from,
                                unsigned char *to, RSA *rsa, int padding);

        int RSA_public_decrypt(int flen, unsigned char *from,
                               unsigned char *to, RSA *rsa, int padding);