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.\" ========================================================================
.\"
.IX Title "BIO_f_cipher 3"
.TH BIO_f_cipher 3 "2017-05-25" "1.0.2l" "OpenSSL"
.SH "NAME"
BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctx \- cipher BIO filter
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& #include <openssl/bio.h>
\& #include <openssl/evp.h>
.Ve
.PP
.Vb 5
\& BIO_METHOD *   BIO_f_cipher(void);
\& void BIO_set_cipher(BIO *b,const EVP_CIPHER *cipher,
\&                unsigned char *key, unsigned char *iv, int enc);
\& int BIO_get_cipher_status(BIO *b)
\& int BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx)
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIBIO_f_cipher()\fR returns the cipher \s-1BIO\s0 method. This is a filter
\&\s-1BIO\s0 that encrypts any data written through it, and decrypts any data
read from it. It is a \s-1BIO\s0 wrapper for the cipher routines
\&\fIEVP_CipherInit()\fR, \fIEVP_CipherUpdate()\fR and \fIEVP_CipherFinal()\fR.
.PP
Cipher BIOs do not support \fIBIO_gets()\fR or \fIBIO_puts()\fR. 
.PP
\&\fIBIO_flush()\fR on an encryption \s-1BIO\s0 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 \s-1BIO\s0.
.PP
\&\fIBIO_set_cipher()\fR sets the cipher of \s-1BIO\s0 \fBb\fR to \fBcipher\fR using key \fBkey\fR
and \s-1IV\s0 \fBiv\fR. \fBenc\fR should be set to 1 for encryption and zero for
decryption.
.PP
When reading from an encryption \s-1BIO\s0 the final block is automatically
decrypted and checked when \s-1EOF\s0 is detected. \fIBIO_get_cipher_status()\fR
is a \fIBIO_ctrl()\fR macro which can be called to determine whether the
decryption operation was successful.
.PP
\&\fIBIO_get_cipher_ctx()\fR is a \fIBIO_ctrl()\fR macro which retrieves the internal
\&\s-1BIO\s0 cipher context. The retrieved context can be used in conjunction
with the standard cipher routines to set it up. This is useful when
\&\fIBIO_set_cipher()\fR is not flexible enough for the applications needs.
.SH "NOTES"
.IX Header "NOTES"
When encrypting \fIBIO_flush()\fR \fBmust\fR be called to flush the final block
through the \s-1BIO\s0. If it is not then the final block will fail a subsequent
decrypt.
.PP
When decrypting an error on the final block is signalled by a zero
return value from the read operation. A successful decrypt followed
by \s-1EOF\s0 will also return zero for the final read. \fIBIO_get_cipher_status()\fR
should be called to determine if the decrypt was successful.
.PP
As always, if \fIBIO_gets()\fR or \fIBIO_puts()\fR support is needed then it can
be achieved by preceding the cipher \s-1BIO\s0 with a buffering \s-1BIO\s0.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIBIO_f_cipher()\fR returns the cipher \s-1BIO\s0 method.
.PP
\&\fIBIO_set_cipher()\fR does not return a value.
.PP
\&\fIBIO_get_cipher_status()\fR returns 1 for a successful decrypt and 0
for failure.
.PP
\&\fIBIO_get_cipher_ctx()\fR currently always returns 1.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
\&\s-1TBA\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1TBA\s0