Enji Cooper
137 lines
4.6 KiB
Plaintext
137 lines
4.6 KiB
Plaintext
.\" -*- mode: troff; coding: utf-8 -*-
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.\" ========================================================================
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.\"
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.IX Title "BIO_F_CIPHER 3ossl"
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.TH BIO_F_CIPHER 3ossl 2026-01-27 3.5.5 OpenSSL
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH NAME
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BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx \- cipher BIO filter
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.SH SYNOPSIS
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.IX Header "SYNOPSIS"
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.Vb 2
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\& #include <openssl/bio.h>
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\& #include <openssl/evp.h>
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\&
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\& const BIO_METHOD *BIO_f_cipher(void);
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\& int BIO_set_cipher(BIO *b, const EVP_CIPHER *cipher,
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\& const unsigned char *key, const unsigned char *iv, int enc);
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\& int BIO_get_cipher_status(BIO *b);
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\& int BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx);
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.Ve
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.SH DESCRIPTION
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.IX Header "DESCRIPTION"
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\&\fBBIO_f_cipher()\fR returns the cipher BIO method. This is a filter
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BIO that encrypts any data written through it, and decrypts any data
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read from it. It is a BIO wrapper for the cipher routines
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\&\fBEVP_CipherInit()\fR, \fBEVP_CipherUpdate()\fR and \fBEVP_CipherFinal()\fR.
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.PP
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Cipher BIOs do not support \fBBIO_gets()\fR or \fBBIO_puts()\fR.
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.PP
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\&\fBBIO_flush()\fR on an encryption BIO that is being written through is
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used to signal that no more data is to be encrypted: this is used
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to flush and possibly pad the final block through the BIO.
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.PP
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\&\fBBIO_set_cipher()\fR sets the cipher of BIO \fBb\fR to \fBcipher\fR using key \fBkey\fR
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and IV \fBiv\fR. \fBenc\fR should be set to 1 for encryption and zero for
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decryption.
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.PP
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When reading from an encryption BIO the final block is automatically
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decrypted and checked when EOF is detected. \fBBIO_get_cipher_status()\fR
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is a \fBBIO_ctrl()\fR macro which can be called to determine whether the
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decryption operation was successful.
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.PP
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\&\fBBIO_get_cipher_ctx()\fR is a \fBBIO_ctrl()\fR macro which retrieves the internal
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BIO cipher context. The retrieved context can be used in conjunction
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with the standard cipher routines to set it up. This is useful when
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\&\fBBIO_set_cipher()\fR is not flexible enough for the applications needs.
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.SH NOTES
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.IX Header "NOTES"
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When encrypting \fBBIO_flush()\fR \fBmust\fR be called to flush the final block
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through the BIO. If it is not then the final block will fail a subsequent
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decrypt.
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.PP
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When decrypting an error on the final block is signaled by a zero
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return value from the read operation. A successful decrypt followed
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by EOF will also return zero for the final read. \fBBIO_get_cipher_status()\fR
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should be called to determine if the decrypt was successful.
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.PP
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As always, if \fBBIO_gets()\fR or \fBBIO_puts()\fR support is needed then it can
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be achieved by preceding the cipher BIO with a buffering BIO.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fBBIO_f_cipher()\fR returns the cipher BIO method.
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.PP
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\&\fBBIO_set_cipher()\fR returns 1 for success and 0 for failure.
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.PP
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\&\fBBIO_get_cipher_status()\fR returns 1 for a successful decrypt and <=0
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for failure.
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.PP
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\&\fBBIO_get_cipher_ctx()\fR returns 1 for success and <=0 for failure.
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.SH COPYRIGHT
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.IX Header "COPYRIGHT"
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Copyright 2000\-2020 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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