.\"	$NetBSD: BIO_f_md.3,v 1.3 2002/02/07 09:24:08 ross Exp $
.\"
.\" Automatically generated by Pod::Man version 1.02
.\" Thu Apr 12 19:26:38 2001
.\"
.\" Standard preamble:
.\" ======================================================================
.de Sh \" Subsection heading
.br
.if t .Sp
.ne 5
.PP
\fB\\$1\fR
.PP
..
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Ip \" List item
.br
.ie \\n(.$>=3 .ne \\$3
.el .ne 3
.IP "\\$1" \\$2
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R

.fi
..
.\" Set up some character translations and predefined strings.  \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote.  | will give a
.\" real vertical bar.  \*(C+ will give a nicer C++.  Capital omega is used
.\" to do unbreakable dashes and therefore won't be available.  \*(C` and
.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<>
.tr \(*W-|\(bv\*(Tr
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
.    ds -- \(*W-
.    ds PI pi
.    if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
.    if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\"  diablo 12 pitch
.    ds L" ""
.    ds R" ""
.    ds C` `
.    ds C' '
'br\}
.el\{\
.    ds -- \|\(em\|
.    ds PI \(*p
.    ds L" ``
.    ds R" ''
'br\}
.\"
.\" If the F register is turned on, we'll generate index entries on stderr
.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
.\" index entries marked with X<> in POD.  Of course, you'll have to process
.\" the output yourself in some meaningful fashion.
.if \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
.    .
.    nr % 0
.    rr F
.\}
.\"
.\" For nroff, turn off justification.  Always turn off hyphenation; it
.\" makes way too many mistakes in technical documents.
.hy 0
.if n .na
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear.  Run.  Save yourself.  No user-serviceable parts.
.bd B 3
.    \" fudge factors for nroff and troff
.if n \{\
.    ds #H 0
.    ds #V .8m
.    ds #F .3m
.    ds #[ \f1
.    ds #] \fP
.\}
.if t \{\
.    ds #H ((1u-(\\\\n(.fu%2u))*.13m)
.    ds #V .6m
.    ds #F 0
.    ds #[ \&
.    ds #] \&
.\}
.    \" simple accents for nroff and troff
.if n \{\
.    ds ' \&
.    ds ` \&
.    ds ^ \&
.    ds , \&
.    ds ~ ~
.    ds /
.\}
.if t \{\
.    ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
.    ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
.    ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
.    ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
.    ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
.    ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
.    \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
.    \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
.    \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
.    ds : e
.    ds 8 ss
.    ds o a
.    ds d- d\h'-1'\(ga
.    ds D- D\h'-1'\(hy
.    ds th \o'bp'
.    ds Th \o'LP'
.    ds ae ae
.    ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ======================================================================
.\"
.IX Title "BIO_f_md 3"
.TH BIO_f_md 3 "0.9.6a" "2001-04-12" "OpenSSL"
.UC
.SH "NAME"
BIO_f_md, BIO_set_md, BIO_get_md, BIO_get_md_ctx \- message digest \s-1BIO\s0 filter
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& #include \*[Lt]openssl/bio.h\*[Gt]
\& #include \*[Lt]openssl/evp.h\*[Gt]
.Ve
.Vb 4
\& BIO_METHOD *   BIO_f_md(void);
\& int BIO_set_md(BIO *b,EVP_MD *md);
\& int BIO_get_md(BIO *b,EVP_MD **mdp);
\& int BIO_get_md_ctx(BIO *b,EVP_MD_CTX **mdcp);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIBIO_f_md()\fR returns the message digest \s-1BIO\s0 method. This is a filter
\&\s-1BIO\s0 that digests any data passed through it, it is a \s-1BIO\s0 wrapper
for the digest routines \fIEVP_DigestInit()\fR, \fIEVP_DigestUpdate()\fR
and \fIEVP_DigestFinal()\fR.
.PP
Any data written or read through a digest \s-1BIO\s0 using \fIBIO_read()\fR and
\&\fIBIO_write()\fR is digested.
.PP
\&\fIBIO_gets()\fR, if its \fBsize\fR parameter is large enough finishes the
digest calculation and returns the digest value. \fIBIO_puts()\fR is
not supported.
.PP
\&\fIBIO_reset()\fR reinitializes a digest \s-1BIO\s0.
.PP
\&\fIBIO_set_md()\fR sets the message digest of \s-1BIO\s0 \fBb\fR to \fBmd\fR: this
must be called to initialize a digest \s-1BIO\s0 before any data is
passed through it. It is a \fIBIO_ctrl()\fR macro.
.PP
\&\fIBIO_get_md()\fR places the a pointer to the digest BIOs digest method
in \fBmdp\fR, it is a \fIBIO_ctrl()\fR macro.
.PP
\&\fIBIO_get_md_ctx()\fR returns the digest BIOs context into \fBmdcp\fR.
.SH "NOTES"
.IX Header "NOTES"
The context returned by \fIBIO_get_md_ctx()\fR can be used in calls
to \fIEVP_DigestFinal()\fR and also the signature routines \fIEVP_SignFinal()\fR
and \fIEVP_VerifyFinal()\fR.
.PP
The context returned by \fIBIO_get_md_ctx()\fR is an internal context
structure. Changes made to this context will affect the digest
\&\s-1BIO\s0 itself and the context pointer will become invalid when the digest
\&\s-1BIO\s0 is freed.
.PP
After the digest has been retrieved from a digest \s-1BIO\s0 it must be
reinitialized by calling \fIBIO_reset()\fR, or \fIBIO_set_md()\fR before any more
data is passed through it.
.PP
If an application needs to call \fIBIO_gets()\fR or \fIBIO_puts()\fR through
a chain containing digest BIOs then this can be done by prepending
a buffering \s-1BIO\s0.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIBIO_f_md()\fR returns the digest \s-1BIO\s0 method.
.PP
\&\fIBIO_set_md()\fR, \fIBIO_get_md()\fR and \fIBIO_md_ctx()\fR return 1 for success and
0 for failure.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
The following example creates a \s-1BIO\s0 chain containing an \s-1SHA1\s0 and \s-1MD5\s0
digest \s-1BIO\s0 and passes the string \*(L"Hello World\*(R" through it. Error
checking has been omitted for clarity.
.PP
.Vb 14
\& BIO *bio, *mdtmp;
\& char message[] = "Hello World";
\& bio = BIO_new(BIO_s_null());
\& mdtmp = BIO_new(BIO_f_md());
\& BIO_set_md(mdtmp, EVP_sha1());
\& /* For BIO_push() we want to append the sink BIO and keep a note of
\&  * the start of the chain.
\&  */
\& bio = BIO_push(mdtmp, bio);
\& mdtmp = BIO_new(BIO_f_md());
\& BIO_set_md(mdtmp, EVP_md5());
\& bio = BIO_push(mdtmp, bio);
\& /* Note: mdtmp can now be discarded */
\& BIO_write(bio, message, strlen(message));
.Ve
The next example digests data by reading through a chain instead:
.PP
.Vb 14
\& BIO *bio, *mdtmp;
\& char buf[1024];
\& int rdlen;
\& bio = BIO_new_file(file, "rb");
\& mdtmp = BIO_new(BIO_f_md());
\& BIO_set_md(mdtmp, EVP_sha1());
\& bio = BIO_push(mdtmp, bio);
\& mdtmp = BIO_new(BIO_f_md());
\& BIO_set_md(mdtmp, EVP_md5());
\& bio = BIO_push(mdtmp, bio);
\& do {
\&        rdlen = BIO_read(bio, buf, sizeof(buf));
\&        /* Might want to do something with the data here */
\& } while(rdlen \*[Gt] 0);
.Ve
This next example retrieves the message digests from a \s-1BIO\s0 chain and
outputs them. This could be used with the examples above.
.PP
.Vb 16
\& BIO *mdtmp;
\& unsigned char mdbuf[EVP_MAX_MD_SIZE];
\& int mdlen;
\& int i;
\& mdtmp = bio;   /* Assume bio has previously been set up */
\& do {
\&        EVP_MD *md;
\&        mdtmp = BIO_find_type(mdtmp, BIO_TYPE_MD);
\&        if(!mdtmp) break;
\&        BIO_get_md(mdtmp, \*[Am]md);
\&        printf("%s digest", OBJ_nid2sn(EVP_MD_type(md)));
\&        mdlen = BIO_gets(mdtmp, mdbuf, EVP_MAX_MD_SIZE);
\&        for(i = 0; i \*[Lt] mdlen; i++) printf(":%02X", mdbuf[i]);
\&        printf("\en");
\&        mdtmp = BIO_next(mdtmp);
\& } while(mdtmp);
.Ve
.Vb 1
\& BIO_free_all(bio);
.Ve
.SH "BUGS"
.IX Header "BUGS"
The lack of support for \fIBIO_puts()\fR and the non standard behaviour of
\&\fIBIO_gets()\fR could be regarded as anomalous. It could be argued that \fIBIO_gets()\fR
and \fIBIO_puts()\fR should be passed to the next \s-1BIO\s0 in the chain and digest
the data passed through and that digests should be retrieved using a
separate \fIBIO_ctrl()\fR call.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1TBA\s0