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.

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.\" ========================================================================
.\"
.IX Title "Digest::MD5 3"
.TH Digest::MD5 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Digest::MD5 \- Perl interface to the MD5 Algorithm
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& # Functional style
\& use Digest::MD5 qw(md5 md5_hex md5_base64);
\&
\& $digest = md5($data);
\& $digest = md5_hex($data);
\& $digest = md5_base64($data);
\&
\& # OO style
\& use Digest::MD5;
\&
\& $ctx = Digest::MD5\->new;
\&
\& $ctx\->add($data);
\& $ctx\->addfile(*FILE);
\&
\& $digest = $ctx\->digest;
\& $digest = $ctx\->hexdigest;
\& $digest = $ctx\->b64digest;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`Digest::MD5\*(C'\fR module allows you to use the \s-1RSA\s0 Data Security
Inc. \s-1MD5\s0 Message Digest algorithm from within Perl programs.  The
algorithm takes as input a message of arbitrary length and produces as
output a 128\-bit \*(L"fingerprint\*(R" or \*(L"message digest\*(R" of the input.
.PP
Note that the \s-1MD5\s0 algorithm is not as strong as it used to be.  It has
since 2005 been easy to generate different messages that produce the
same \s-1MD5\s0 digest.  It still seems hard to generate messages that
produce a given digest, but it is probably wise to move to stronger
algorithms for applications that depend on the digest to uniquely identify
a message.
.PP
The \f(CW\*(C`Digest::MD5\*(C'\fR module provide a procedural interface for simple
use, as well as an object oriented interface that can handle messages
of arbitrary length and which can read files directly.
.SH "FUNCTIONS"
.IX Header "FUNCTIONS"
The following functions are provided by the \f(CW\*(C`Digest::MD5\*(C'\fR module.
None of these functions are exported by default.
.IP "md5($data,...)" 4
.IX Item "md5($data,...)"
This function will concatenate all arguments, calculate the \s-1MD5\s0 digest
of this \*(L"message\*(R", and return it in binary form.  The returned string
will be 16 bytes long.
.Sp
The result of md5(\*(L"a\*(R", \*(L"b\*(R", \*(L"c\*(R") will be exactly the same as the
result of md5(\*(L"abc\*(R").
.IP "md5_hex($data,...)" 4
.IX Item "md5_hex($data,...)"
Same as \fImd5()\fR, but will return the digest in hexadecimal form. The
length of the returned string will be 32 and it will only contain
characters from this set: '0'..'9' and 'a'..'f'.
.IP "md5_base64($data,...)" 4
.IX Item "md5_base64($data,...)"
Same as \fImd5()\fR, but will return the digest as a base64 encoded string.
The length of the returned string will be 22 and it will only contain
characters from this set: 'A'..'Z', 'a'..'z', '0'..'9', '+' and
\&'/'.
.Sp
Note that the base64 encoded string returned is not padded to be a
multiple of 4 bytes long.  If you want interoperability with other
base64 encoded md5 digests you might want to append the redundant
string \*(L"==\*(R" to the result.
.SH "METHODS"
.IX Header "METHODS"
The object oriented interface to \f(CW\*(C`Digest::MD5\*(C'\fR is described in this
section.  After a \f(CW\*(C`Digest::MD5\*(C'\fR object has been created, you will add
data to it and finally ask for the digest in a suitable format.  A
single object can be used to calculate multiple digests.
.PP
The following methods are provided:
.ie n .IP "$md5 = Digest::MD5\->new" 4
.el .IP "\f(CW$md5\fR = Digest::MD5\->new" 4
.IX Item "$md5 = Digest::MD5->new"
The constructor returns a new \f(CW\*(C`Digest::MD5\*(C'\fR object which encapsulate
the state of the \s-1MD5\s0 message-digest algorithm.
.Sp
If called as an instance method (i.e. \f(CW$md5\fR\->new) it will just reset the
state the object to the state of a newly created object.  No new
object is created in this case.
.ie n .IP "$md5\->reset" 4
.el .IP "\f(CW$md5\fR\->reset" 4
.IX Item "$md5->reset"
This is just an alias for \f(CW$md5\fR\->new.
.ie n .IP "$md5\->clone" 4
.el .IP "\f(CW$md5\fR\->clone" 4
.IX Item "$md5->clone"
This a copy of the \f(CW$md5\fR object. It is useful when you do not want to