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      1 =pod
      2 
      3 =head1 NAME
      4 
      5 BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx - cipher BIO filter
      6 
      7 =head1 SYNOPSIS
      8 
      9 =for openssl multiple includes
     10 
     11  #include <openssl/bio.h>
     12  #include <openssl/evp.h>
     13 
     14  const BIO_METHOD *BIO_f_cipher(void);
     15  int BIO_set_cipher(BIO *b, const EVP_CIPHER *cipher,
     16                     const unsigned char *key, const unsigned char *iv, int enc);
     17  int BIO_get_cipher_status(BIO *b);
     18  int BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx);
     19 
     20 =head1 DESCRIPTION
     21 
     22 BIO_f_cipher() returns the cipher BIO method. This is a filter
     23 BIO that encrypts any data written through it, and decrypts any data
     24 read from it. It is a BIO wrapper for the cipher routines
     25 EVP_CipherInit(), EVP_CipherUpdate() and EVP_CipherFinal().
     26 
     27 Cipher BIOs do not support BIO_gets() or BIO_puts().
     28 
     29 BIO_flush() on an encryption BIO that is being written through is
     30 used to signal that no more data is to be encrypted: this is used
     31 to flush and possibly pad the final block through the BIO.
     32 
     33 BIO_set_cipher() sets the cipher of BIO B<b> to B<cipher> using key B<key>
     34 and IV B<iv>. B<enc> should be set to 1 for encryption and zero for
     35 decryption.
     36 
     37 When reading from an encryption BIO the final block is automatically
     38 decrypted and checked when EOF is detected. BIO_get_cipher_status()
     39 is a BIO_ctrl() macro which can be called to determine whether the
     40 decryption operation was successful.
     41 
     42 BIO_get_cipher_ctx() is a BIO_ctrl() macro which retrieves the internal
     43 BIO cipher context. The retrieved context can be used in conjunction
     44 with the standard cipher routines to set it up. This is useful when
     45 BIO_set_cipher() is not flexible enough for the applications needs.
     46 
     47 =head1 NOTES
     48 
     49 When encrypting BIO_flush() B<must> be called to flush the final block
     50 through the BIO. If it is not then the final block will fail a subsequent
     51 decrypt.
     52 
     53 When decrypting an error on the final block is signaled by a zero
     54 return value from the read operation. A successful decrypt followed
     55 by EOF will also return zero for the final read. BIO_get_cipher_status()
     56 should be called to determine if the decrypt was successful.
     57 
     58 As always, if BIO_gets() or BIO_puts() support is needed then it can
     59 be achieved by preceding the cipher BIO with a buffering BIO.
     60 
     61 =head1 RETURN VALUES
     62 
     63 BIO_f_cipher() returns the cipher BIO method.
     64 
     65 BIO_set_cipher() returns 1 for success and 0 for failure.
     66 
     67 BIO_get_cipher_status() returns 1 for a successful decrypt and <=0
     68 for failure.
     69 
     70 BIO_get_cipher_ctx() returns 1 for success and <=0 for failure.
     71 
     72 =head1 COPYRIGHT
     73 
     74 Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
     75 
     76 Licensed under the Apache License 2.0 (the "License").  You may not use
     77 this file except in compliance with the License.  You can obtain a copy
     78 in the file LICENSE in the source distribution or at
     79 L<https://www.openssl.org/source/license.html>.
     80 
     81 =cut
     82