NAME
BIO_f_cipher,
BIO_set_cipher,
BIO_get_cipher_status,
BIO_get_cipher_ctx —
cipher BIO filter
SYNOPSIS
#include
<openssl/bio.h>
#include <openssl/evp.h>
const BIO_METHOD *
BIO_f_cipher(void);
int
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);
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(3),
EVP_CipherUpdate(3), and
EVP_CipherFinal(3).
Cipher BIOs do not support BIO_gets(3) or BIO_puts(3).
BIO_flush(3) 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(3) macro which can be called to determine whether
the decryption operation was successful.
BIO_get_cipher_ctx()
is a BIO_ctrl(3) 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 a chain containing a cipher BIO is copied with BIO_dup_chain(3), the cipher context is automatically copied from the existing BIO object to the new one and the init flag that can be retrieved with BIO_get_init(3) is set to 1.
When encrypting, BIO_flush(3) 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(3) or BIO_puts(3) support is needed, then it can be achieved by preceding the cipher BIO with a buffering BIO.
RETURN VALUES
BIO_f_cipher() returns the cipher BIO
method. BIO_set_cipher() returns 1 on success and 0
on error.
BIO_get_cipher_status() returns 1 for a
successful decrypt and 0 for failure.
BIO_get_cipher_ctx() currently always
returns 1.
SEE ALSO
HISTORY
BIO_f_cipher(),
BIO_set_cipher(), and
BIO_get_cipher_status() first appeared in SSLeay
0.6.5 and have been available since OpenBSD 2.4.
BIO_get_cipher_ctx() first appeared in
SSLeay 0.9.1 and has been available since OpenBSD
2.6.