BIO_F_CIPHER(3)            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

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);

     long
     BIO_get_cipher_status(BIO *b);

     long
     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.

     BIO_ctrl(3) cmd arguments correspond to macros as follows:

        cmd constant               corresponding macro
        BIO_C_GET_CIPHER_CTX       BIO_get_cipher_ctx()
        BIO_C_GET_CIPHER_STATUS    BIO_get_cipher_status()
        BIO_CTRL_FLUSH             BIO_flush(3)
        BIO_CTRL_PENDING           BIO_pending(3)
        BIO_CTRL_RESET             BIO_reset(3)
        BIO_CTRL_WPENDING          BIO_wpending(3)

RETURN VALUES
     BIO_f_cipher() returns the cipher BIO method.

     When called on a cipher BIO object, BIO_method_type(3) returns the
     constant BIO_TYPE_CIPHER and BIO_method_name(3) returns a pointer to the
     static string "cipher".

     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
     BIO_new(3), EVP_EncryptInit(3)

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.

Linux 6.8.2-arch2-1             April 29, 2023             Linux 6.8.2-arch2-1