BIO_F_CIPHER(3) BSD Library Functions Manual BIO_F_CIPHER(3)NAME
BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx —
cipher BIO filter
BIO_set_cipher(BIO *b, const EVP_CIPHER *cipher, unsigned char *key,
unsigned char *iv, int enc);
BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx);
DESCRIPTIONBIO_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 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 subse‐
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 VALUESBIO_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.
BSD July 17, 2014 BSD