=pod

=head1 NAME

BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx - cipher BIO filter

=head1 SYNOPSIS

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

 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 signalled 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 EXAMPLES

TBA

=head1 SEE ALSO

TBA