## 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 applications.
`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`

.

`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.

## 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).

## SEE ALSO

## STANDARDS

SSL, PKCS #1 v2.0

## HISTORY

`RSA_public_encrypt`

() and
`RSA_private_decrypt`

() appeared in SSLeay 0.4 or
earlier and have been available since OpenBSD
2.4.

`RSA_NO_PADDING`

is available since SSLeay
0.9.0. OAEP was added in OpenSSL 0.9.2b.

## BUGS

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`

.