Update documentation regarding required output buffer memory size

 #include <openssl/rsa.h>

 int RSA_public_encrypt(int flen, unsigned char *from,

 int RSA_public_encrypt(int flen, const unsigned char *from,

                        unsigned char *to, RSA *rsa, int padding);

 int RSA_private_decrypt(int flen, unsigned char *from,

 int RSA_private_decrypt(int flen, const unsigned char *from,

                         unsigned char *to, RSA *rsa, int padding);

=head1 DESCRIPTION

=item RSA_PKCS1_PADDING

PKCS #1 v1.5 padding. This currently is the most widely used mode.

However, it is highly recommended to use RSA_PKCS1_OAEP_PADDING in

new applications. SEE WARNING BELOW.

=item RSA_PKCS1_OAEP_PADDING

=back

B<flen> must be less than RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5

based padding modes, less than RSA_size(B<rsa>) - 41 for

B<flen> must not be more than RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5

based padding modes, not more than RSA_size(B<rsa>) - 42 for

RSA_PKCS1_OAEP_PADDING and exactly RSA_size(B<rsa>) for RSA_NO_PADDING.

The random number generator must be seeded prior to calling

RSA_public_encrypt().

When a padding mode other than RSA_NO_PADDING is in use, then

RSA_public_encrypt() will include some random bytes into the ciphertext

and therefore the ciphertext will be different each time, even if the

plaintext and the public key are exactly identical.

The returned ciphertext in B<to> will always be zero padded to exactly

RSA_size(B<rsa>) bytes.

B<to> and B<from> may overlap.

RSA_private_decrypt() decrypts the B<flen> bytes at B<from> using the

private key B<rsa> and stores the plaintext in B<to>. B<to> must point

to a memory section large enough to hold the decrypted data (which is

smaller than RSA_size(B<rsa>)). B<padding> is the padding mode that

was used to encrypt the data.

private key B<rsa> and stores the plaintext in B<to>. B<flen> should

be equal to RSA_size(B<rsa>) but may be smaller, when leading zero

bytes are in the ciphertext. Those are not important and may be removed,

but RSA_public_encrypt() does not do that. B<to> must point

to a memory section large enough to hold the maximal possible decrypted

data (which is equal to RSA_size(B<rsa>) for RSA_NO_PADDING,

RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5 based padding modes and

RSA_size(B<rsa>) - 42 for RSA_PKCS1_OAEP_PADDING).

B<padding> is the padding mode that was used to encrypt the data.

B<to> and B<from> may overlap.

=head1 RETURN VALUES

RSA_public_encrypt() returns the size of the encrypted data (i.e.,

RSA_size(B<rsa>)). RSA_private_decrypt() returns the size of the

recovered plaintext.

recovered plaintext. A return value of 0 is not an error and

means only that the plaintext was empty.

On error, -1 is returned; the error codes can be

obtained by L<ERR_get_error(3)>.

=head1 COPYRIGHT

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

Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy