RSA_private_encrypt.3ossl - Man Page

low-level signature operations


 #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);


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:


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.


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.

Return Values

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).

See Also

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


Both of these functions were deprecated in OpenSSL 3.0.

Referenced By


The man page RSA_public_decrypt.3ossl(3) is an alias of RSA_private_encrypt.3ossl(3).

2024-04-04 3.2.1 OpenSSL