DragonFly On-Line Manual Pages
BIO(3) DragonFly Library Functions Manual BIO(3)
BIO -- I/O abstraction
A BIO is an I/O abstraction, it hides many of the underlying I/O details
from an application. If an application uses a BIO for its I/O, it can
transparently handle SSL connections, unencrypted network connections and
There are two types of BIO, a source/sink BIO and a filter BIO.
As its name implies, a source/sink BIO is a source and/or sink of data,
examples include a socket BIO and a file BIO.
A filter BIO takes data from one BIO and passes it through to another, or
to the application. The data may be left unmodified (for example a mes-
sage digest BIO) or translated (for example an encryption BIO). The
effect of a filter BIO may change according to the I/O operation it is
performing: for example an encryption BIO will encrypt data if it is
being written to and decrypt data if it is being read from.
BIOs can be joined together to form a chain (a single BIO is a chain with
one component). A chain normally consist of one source/sink BIO and one
or more filter BIOs. Data read from or written to the first BIO then
traverses the chain to the end (normally a source/sink BIO).
BIO_ctrl(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3),
BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_find_type(3), BIO_new(3),
BIO_new_bio_pair(3), BIO_push(3), BIO_read(3), BIO_s_accept(3),
BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3), BIO_s_mem(3),
BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3)
DragonFly 4.7 July 17, 2014 DragonFly 4.7
BIO_f_cipher(3) OpenSSL BIO_f_cipher(3)
BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx
- cipher BIO filter
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)
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 to cipher using key key and
IV iv. 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.
When encrypting BIO_flush() must be called to flush the final block
through the BIO. If it is not then the final block will fail a
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.
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
BIO_get_cipher_ctx() currently always returns 1.
1.0.2h 2016-05-03 BIO_f_cipher(3)