=pod

=head1 NAME

BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx - cipher BIO filter

=head1 SYNOPSIS

=for openssl multiple includes

 #include <openssl/bio.h>
 #include <openssl/evp.h>

 const BIO_METHOD *BIO_f_cipher(void);
 void BIO_set_cipher(BIO *b, const EVP_CIPHER *cipher,
                     unsigned char *key, unsigned char *iv, int enc);
 int BIO_get_cipher_status(BIO *b);
 int BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx);

=head1 DESCRIPTION

BIO_f_cipher() returns the cipher BIO method. This is a filter
BIO that encrypts any data written through it, and decrypts any data
read from it. It is a BIO wrapper for the cipher routines
EVP_CipherInit(), EVP_CipherUpdate() and EVP_CipherFinal().

Cipher BIOs do not support BIO_gets() or BIO_puts().

BIO_flush() on an encryption BIO that is being written through is
used to signal that no more data is to be encrypted: this is used
to flush and possibly pad the final block through the BIO.

BIO_set_cipher() sets the cipher of BIO B<b> to B<cipher> using key B<key>
and IV B<iv>. B<enc> should be set to 1 for encryption and zero for
decryption.

When reading from an encryption BIO the final block is automatically
decrypted and checked when EOF is detected. BIO_get_cipher_status()
is a BIO_ctrl() macro which can be called to determine whether the
decryption operation was successful.

BIO_get_cipher_ctx() is a BIO_ctrl() macro which retrieves the internal
BIO cipher context. The retrieved context can be used in conjunction
with the standard cipher routines to set it up. This is useful when
BIO_set_cipher() is not flexible enough for the applications needs.

=head1 NOTES

When encrypting BIO_flush() B<must> be called to flush the final block
through the BIO. If it is not then the final block will fail a subsequent
decrypt.

When decrypting an error on the final block is signaled by a zero
return value from the read operation. A successful decrypt followed
by EOF will also return zero for the final read. BIO_get_cipher_status()
should be called to determine if the decrypt was successful.

As always, if BIO_gets() or BIO_puts() support is needed then it can
be achieved by preceding the cipher BIO with a buffering BIO.

=head1 RETURN VALUES

BIO_f_cipher() returns the cipher BIO method.

BIO_set_cipher() does not return a value.

BIO_get_cipher_status() returns 1 for a successful decrypt and 0
for failure.

BIO_get_cipher_ctx() currently always returns 1.

=head1 COPYRIGHT

Copyright 2000-2020 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
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
