# RSA_public_encrypt.3ssl man page

RSA_public_encrypt, RSA_private_decrypt — RSA public key cryptography

## Synopsis

`#include <openssl/rsa.h>`

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

```
int RSA_private_decrypt(int flen, 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_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 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.

## 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).

## Conforming to

SSL, PKCS #1 v2.0

## See Also

ERR_get_error(3), rand(3), RSA_size(3)

## Copyright

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.….

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