digest::md5.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

destroy the digests state, but need an intermediate value of the
digest, e.g. when calculating digests iteratively on a continuous data
stream.  Example:
.Sp
.Vb 5
\&    my $md5 = Digest::MD5\->new;
\&    while (<>) {
\&        $md5\->add($_);
\&        print "Line $.: ", $md5\->clone\->hexdigest, "\en";
\&    }
.Ve
.ie n .IP "$md5\->add($data,...)" 4
.el .IP "\f(CW$md5\fR\->add($data,...)" 4
.IX Item "$md5->add($data,...)"
The \f(CW$data\fR provided as argument are appended to the message we
calculate the digest for.  The return value is the \f(CW$md5\fR object itself.
.Sp
All these lines will have the same effect on the state of the \f(CW$md5\fR
object:
.Sp
.Vb 4
\&    $md5\->add("a"); $md5\->add("b"); $md5\->add("c");
\&    $md5\->add("a")\->add("b")\->add("c");
\&    $md5\->add("a", "b", "c");
\&    $md5\->add("abc");
.Ve
.ie n .IP "$md5\->addfile($io_handle)" 4
.el .IP "\f(CW$md5\fR\->addfile($io_handle)" 4
.IX Item "$md5->addfile($io_handle)"
The \f(CW$io_handle\fR will be read until \s-1EOF\s0 and its content appended to the
message we calculate the digest for.  The return value is the \f(CW$md5\fR
object itself.
.Sp
The \fIaddfile()\fR method will \fIcroak()\fR if it fails reading data for some
reason.  If it croaks it is unpredictable what the state of the \f(CW$md5\fR
object will be in. The \fIaddfile()\fR method might have been able to read
the file partially before it failed.  It is probably wise to discard
or reset the \f(CW$md5\fR object if this occurs.
.Sp
In most cases you want to make sure that the \f(CW$io_handle\fR is in
\&\f(CW\*(C`binmode\*(C'\fR before you pass it as argument to the \fIaddfile()\fR method.
.ie n .IP "$md5\fR\->add_bits($data, \f(CW$nbits)" 4
.el .IP "\f(CW$md5\fR\->add_bits($data, \f(CW$nbits\fR)" 4
.IX Item "$md5->add_bits($data, $nbits)"
.PD 0
.ie n .IP "$md5\->add_bits($bitstring)" 4
.el .IP "\f(CW$md5\fR\->add_bits($bitstring)" 4
.IX Item "$md5->add_bits($bitstring)"
.PD
Since the \s-1MD5\s0 algorithm is byte oriented you might only add bits as
multiples of 8, so you probably want to just use \fIadd()\fR instead.  The
\&\fIadd_bits()\fR method is provided for compatibility with other digest
implementations.  See Digest for description of the arguments
that \fIadd_bits()\fR take.
.ie n .IP "$md5\->digest" 4
.el .IP "\f(CW$md5\fR\->digest" 4
.IX Item "$md5->digest"
Return the binary digest for the message.  The returned string will be
16 bytes long.
.Sp
Note that the \f(CW\*(C`digest\*(C'\fR operation is effectively a destructive,
read-once operation. Once it has been performed, the \f(CW\*(C`Digest::MD5\*(C'\fR
object is automatically \f(CW\*(C`reset\*(C'\fR and can be used to calculate another
digest value.  Call \f(CW$md5\fR\->clone\->digest if you want to calculate the
digest without resetting the digest state.
.ie n .IP "$md5\->hexdigest" 4
.el .IP "\f(CW$md5\fR\->hexdigest" 4
.IX Item "$md5->hexdigest"
Same as \f(CW$md5\fR\->digest, but will return the digest in hexadecimal
form. The length of the returned string will be 32 and it will only
contain characters from this set: '0'..'9' and 'a'..'f'.
.ie n .IP "$md5\->b64digest" 4
.el .IP "\f(CW$md5\fR\->b64digest" 4
.IX Item "$md5->b64digest"
Same as \f(CW$md5\fR\->digest, but will return the digest as a base64 encoded
string.  The length of the returned string will be 22 and it will only
contain characters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+'
and '/'.
.Sp
The base64 encoded string returned is not padded to be a multiple of 4
bytes long.  If you want interoperability with other base64 encoded
md5 digests you might want to append the string \*(L"==\*(R" to the result.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
The simplest way to use this library is to import the \fImd5_hex()\fR
function (or one of its cousins):
.PP
.Vb 2
\&    use Digest::MD5 qw(md5_hex);
\&    print "Digest is ", md5_hex("foobarbaz"), "\en";
.Ve
.PP
The above example would print out the message:
.PP
.Vb 1
\&    Digest is 6df23dc03f9b54cc38a0fc1483df6e21
.Ve
.PP
The same checksum can also be calculated in \s-1OO\s0 style:
.PP
.Vb 1
\&    use Digest::MD5;
\&    
\&    $md5 = Digest::MD5\->new;
\&    $md5\->add(\*(Aqfoo\*(Aq, \*(Aqbar\*(Aq);
\&    $md5\->add(\*(Aqbaz\*(Aq);
\&    $digest = $md5\->hexdigest;
\&    
\&    print "Digest is $digest\en";
.Ve
.PP
With \s-1OO\s0 style you can break the message arbitrary.  This means that we
are no longer limited to have space for the whole message in memory, i.e.
we can handle messages of any size.
.PP
This is useful when calculating checksum for files:
.PP
.Vb 1
\&    use Digest::MD5;
\&
\&    my $file = shift || "/etc/passwd";
\&    open(FILE, $file) or die "Can\*(Aqt open \*(Aq$file\*(Aq: $!";
\&    binmode(FILE);
\&
\&    $md5 = Digest::MD5\->new;
\&    while (<FILE>) {
\&        $md5\->add($_);
\&    }
\&    close(FILE);
\&    print $md5\->b64digest, " $file\en";
.Ve
.PP
Or we can use the addfile method for more efficient reading of
the file:
.PP
.Vb 1
\&    use Digest::MD5;
\&
\&    my $file = shift || "/etc/passwd";
\&    open(FILE, $file) or die "Can\*(Aqt open \*(Aq$file\*(Aq: $!";
\&    binmode(FILE);
\&
\&    print Digest::MD5\->new\->addfile(*FILE)\->hexdigest, " $file\en";
.Ve
.PP
Perl 5.8 support Unicode characters in strings.  Since the \s-1MD5\s0
algorithm is only defined for strings of bytes, it can not be used on
strings that contains chars with ordinal number above 255.  The \s-1MD5\s0
functions and methods will croak if you try to feed them such input
data:
.PP
.Vb 1
\&    use Digest::MD5 qw(md5_hex);
\&
\&    my $str = "abc\ex{300}";
\&    print md5_hex($str), "\en";  # croaks
\&    # Wide character in subroutine entry
.Ve
.PP
What you can do is calculate the \s-1MD5\s0 checksum of the \s-1UTF\-8\s0
representation of such strings.  This is achieved by filtering the
string through \fIencode_utf8()\fR function:
.PP
.Vb 2
\&    use Digest::MD5 qw(md5_hex);
\&    use Encode qw(encode_utf8);
\&
\&    my $str = "abc\ex{300}";
\&    print md5_hex(encode_utf8($str)), "\en";
\&    # 8c2d46911f3f5a326455f0ed7a8ed3b3
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Digest,
Digest::MD2,
Digest::SHA1,
Digest::HMAC
.PP
\&\fImd5sum\fR\|(1)
.PP
\&\s-1RFC\s0 1321
.PP
http://en.wikipedia.org/wiki/MD5
.PP
The paper \*(L"How to Break \s-1MD5\s0 and Other Hash Functions\*(R" by Xiaoyun Wang
and Hongbo Yu.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
.PP
.Vb 3
\& Copyright 1998\-2003 Gisle Aas.
\& Copyright 1995\-1996 Neil Winton.
\& Copyright 1991\-1992 RSA Data Security, Inc.
.Ve
.PP
The \s-1MD5\s0 algorithm is defined in \s-1RFC\s0 1321. This implementation is
derived from the reference C code in \s-1RFC\s0 1321 which is covered by
the following copyright statement:
.IP "\(bu" 4
Copyright (C) 1991\-2, \s-1RSA\s0 Data Security, Inc. Created 1991. All
rights reserved.
.Sp
License to copy and use this software is granted provided that it
is identified as the \*(L"\s-1RSA\s0 Data Security, Inc. \s-1MD5\s0 Message-Digest
Algorithm\*(R" in all material mentioning or referencing this software
or this function.
.Sp
License is also granted to make and use derivative works provided
that such works are identified as \*(L"derived from the \s-1RSA\s0 Data
Security, Inc. \s-1MD5\s0 Message-Digest Algorithm\*(R" in all material
mentioning or referencing the derived work.
.Sp
\&\s-1RSA\s0 Data Security, Inc. makes no representations concerning either
the merchantability of this software or the suitability of this
software for any particular purpose. It is provided \*(L"as is\*(R"
without express or implied warranty of any kind.
.Sp
These notices must be retained in any copies of any part of this
documentation and/or software.
.PP
This copyright does not prohibit distribution of any version of Perl
containing this extension under the terms of the \s-1GNU\s0 or Artistic
licenses.
.SH "AUTHORS"
.IX Header "AUTHORS"
The original \f(CW\*(C`MD5\*(C'\fR interface was written by Neil Winton
(\f(CW\*(C`[e-mail]\*(C'\fR).
.PP
The \f(CW\*(C`Digest::MD5\*(C'\fR module is written by Gisle Aas <[e-mail]>.