RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography
#include <openssl/rsa.h>
int RSA_public_encrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
int RSA_private_decrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
RSA_public_encrypt() encrypts the flen bytes at from (usually a session key) using the public key rsa and stores the ciphertext 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 currently is the most widely used mode.
EME-OAEP as defined in PKCS #1 v2.0 with SHA-1, MGF1 and an empty encoding parameter. This mode is recommended for all new applications.
PKCS #1 v1.5 padding with an SSL-specific modification that denotes that the server is SSL3 capable.
Raw RSA encryption. This mode should only be used to implement cryptographically sound padding modes in the application code. Encrypting user data directly with RSA is insecure.
flen must be less than RSA_size(rsa) - 11 for the PKCS #1 v1.5 based padding modes, less than RSA_size(rsa) - 41 for RSA_PKCS1_OAEP_PADDING and exactly RSA_size(rsa) for RSA_NO_PADDING. The random number generator must be seeded prior to calling RSA_public_encrypt().
RSA_private_decrypt() decrypts the flen bytes at from using the private key rsa and stores the plaintext in to. to must point to a memory section large enough to hold the decrypted data (which is smaller than RSA_size(rsa)). padding is the padding mode that was used to encrypt the data.
RSA_public_encrypt() returns the size of the encrypted data (i.e., RSA_size(rsa)). RSA_private_decrypt() returns the size of the recovered plaintext.
On error, -1 is returned; the error codes can be obtained by ERR_get_error(3).
Decryption failures in the RSA_PKCS1_PADDING mode leak information which can potentially be used to mount a Bleichenbacher padding oracle attack. This is an inherent weakness in the PKCS #1 v1.5 padding design. Prefer RSA_PKCS1_OAEP_PADDING.
SSL, PKCS #1 v2.0
ERR_get_error(3), rand(3), rsa(3), RSA_size(3)
The padding argument was added in SSLeay 0.8. RSA_NO_PADDING is available since SSLeay 0.9.0, OAEP was added in OpenSSL 0.9.2b.