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,
                           const unsigned char *key, const 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(), 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.

NOTES

       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 subsequent decrypt.

       When decrypting an error on the final block is signaled 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.

RETURN VALUES

       BIO_f_cipher() returns the cipher BIO method.

       BIO_set_cipher() returns 1 for success and 0 for failure.

       BIO_get_cipher_status() returns 1 for a successful decrypt and <=0 for failure.

       BIO_get_cipher_ctx() returns 1 for success and <=0 for failure.

COPYRIGHT

       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.