# /usr/man/cat.3/RSA_public_encrypt.3.Z

## NAME

RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography

## SYNOPSIS

#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);

## DESCRIPTION

*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:
RSA_PKCS1_PADDING
PKCS #1 v1.5 padding. This currently is the most widely used mode.
RSA_PKCS1_OAEP_PADDING
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 applica-
tions.
RSA_SSLV23_PADDING
PKCS #1 v1.5 padding with an SSL-specific modification that denotes
that the server is SSL3 capable.
RSA_NO_PADDING
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 gener-
ator 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 sec-
tion 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.

## RETURN VALUES

*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)**.

## WARNING

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.

## CONFORMING TO

SSL, PKCS #1 v2.0

## SEE ALSO

**ERR_get_error(3)**, **rand(3)**, **rsa(3)**, **RSA_size(3)**

## HISTORY

The **padding** argument was added in SSLeay 0.8. RSA_NO_PADDING is avail-
able since SSLeay 0.9.0, OAEP was added in OpenSSL 0.9.2b.
1.0.2t 2019-09-10 **RSA_public_encrypt(3)**
See also **RSA_private_decrypt(3)**

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