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# $Id: PEM.pm 1829 2005-05-25 21:51:40Z btrott $
package Convert::PEM;
use strict;
use base qw( Class::ErrorHandler );
use MIME::Base64;
use Digest::MD5 qw( md5 );
use Convert::ASN1;
use Carp qw( croak );
use Convert::PEM::CBC;
use vars qw( $VERSION );
$VERSION = '0.07';
sub new {
my $class = shift;
my $pem = bless { }, $class;
$pem->init(@_);
}
sub init {
my $pem = shift;
my %param = @_;
unless (exists $param{ASN} && exists $param{Name}) {
return (ref $pem)->error("init: Name and ASN are required");
}
else {
$pem->{ASN} = $param{ASN};
$pem->{Name} = $param{Name};
}
$pem->{Macro} = $param{Macro};
my $asn = $pem->{_asn} = Convert::ASN1->new;
$asn->prepare( $pem->{ASN} ) or
return (ref $pem)->error("ASN prepare failed: $asn->{error}");
$pem;
}
sub asn { $_[0]->{_asn} }
sub ASN { $_[0]->{ASN} }
sub name { $_[0]->{Name} }
sub read {
my $pem = shift;
my %param = @_;
my $blob;
local *FH;
my $fname = delete $param{Filename};
open FH, $fname or
return $pem->error("Can't open $fname: $!");
$blob = do { local $/; <FH> };
close FH;
$param{Content} = $blob;
$pem->decode(%param);
}
sub write {
my $pem = shift;
my %param = @_;
my $fname = delete $param{Filename} or
return $pem->error("write: Filename is required");
my $blob = $pem->encode(%param);
local *FH;
open FH, ">$fname" or
return $pem->error("Can't open $fname: $!");
print FH $blob;
close FH;
$blob;
}
sub decode {
my $pem = shift;
my %param = @_;
my $blob = $param{Content} or
return $pem->error("'Content' is required");
chomp $blob;
my $dec = $pem->explode($blob) or return;
my $name = $param{Name} || $pem->name;
return $pem->error("Object $dec->{Object} does not match " . $name)
unless $dec->{Object} eq $name;
my $head = $dec->{Headers};
my $buf = $dec->{Content};
my %headers = map { $_->[0] => $_->[1] } @$head;
if (%headers && $headers{'Proc-Type'} eq '4,ENCRYPTED') {
$buf = $pem->decrypt( Ciphertext => $buf,
Info => $headers{'DEK-Info'},
Password => $param{Password} )
or return;
}
my $asn = $pem->asn;
if (my $macro = ($param{Macro} || $pem->{Macro})) {
$asn = $asn->find($macro) or
return $pem->error("Can't find Macro $macro");
}
my $obj = $asn->decode($buf) or
return $pem->error("ASN decode failed: $asn->{error}");
$obj;
}
sub encode {
my $pem = shift;
my %param = @_;
my $asn = $pem->asn;
if (my $macro = ($param{Macro} || $pem->{Macro})) {
$asn = $asn->find($macro) or
return $pem->error("Can't find Macro $macro");
}
my $buf = $asn->encode( $param{Content} ) or
return $pem->error("ASN encode failed: $asn->{error}");
my(@headers);
if ($param{Password}) {
my($info);
($buf, $info) = $pem->encrypt( Plaintext => $buf,
Password => $param{Password} )
or return;
push @headers, [ 'Proc-Type' => '4,ENCRYPTED' ];
push @headers, [ 'DEK-Info' => $info ];
}
$pem->implode( Object => $param{Name} || $pem->name,
Headers => \@headers,
Content => $buf );
}
sub explode {
my $pem = shift;
my($message) = @_;
my($head, $object, $headers, $content, $tail) = $message =~
m:(-----BEGIN ([^\n\-]+)-----)\n(.*?\n\n)?(.+)(-----END .*?-----)$:s;
my $buf = decode_base64($content);
my @headers;
if ($headers) {
for my $h ( split /\n/, $headers ) {
my($k, $v) = split /:\s*/, $h, 2;
push @headers, [ $k => $v ] if $k;
}
}
{ Content => $buf,
Object => $object,
Headers => \@headers }
}
sub implode {
my $pem = shift;
my %param = @_;
my $head = "-----BEGIN $param{Object}-----";
my $tail = "-----END $param{Object}-----";
my $content = encode_base64( $param{Content}, '' );
$content =~ s!(.{1,64})!$1\n!g;
my $headers = join '',
map { "$_->[0]: $_->[1]\n" }
@{ $param{Headers} };
$headers .= "\n" if $headers;
"$head\n$headers$content$tail\n";
}
use vars qw( %CTYPES );
%CTYPES = ('DES-EDE3-CBC' => 'Crypt::DES_EDE3');
sub decrypt {
my $pem = shift;
my %param = @_;
my $passphrase = $param{Password} || "";
my($ctype, $iv) = split /,/, $param{Info};
my $cmod = $CTYPES{$ctype} or
return $pem->error("Unrecognized cipher: '$ctype'");
$iv = pack "H*", $iv;
my $cbc = Convert::PEM::CBC->new(
Passphrase => $passphrase,
Cipher => $cmod,
IV => $iv );
my $buf = $cbc->decrypt($param{Ciphertext}) or
return $pem->error("Decryption failed: " . $cbc->errstr);
$buf;
}
sub encrypt {
my $pem = shift;
my %param = @_;
$param{Password} or return $param{Plaintext};
my $ctype = $param{Cipher} || 'DES-EDE3-CBC';
my $cmod = $CTYPES{$ctype} or
return $pem->error("Unrecognized cipher: '$ctype'");
my $cbc = Convert::PEM::CBC->new(
Passphrase => $param{Password},
Cipher => $cmod );
my $iv = uc join '', unpack "H*", $cbc->iv;
my $buf = $cbc->encrypt($param{Plaintext}) or
return $pem->error("Encryption failed: " . $cbc->errstr);
($buf, "$ctype,$iv");
}
1;
__END__
=head1 NAME
Convert::PEM - Read/write encrypted ASN.1 PEM files
=head1 SYNOPSIS
use Convert::PEM;
my $pem = Convert::PEM->new(
Name => "DSA PRIVATE KEY",
ASN => qq(
DSAPrivateKey SEQUENCE {
version INTEGER,
p INTEGER,
q INTEGER,
g INTEGER,
pub_key INTEGER,
priv_key INTEGER
}
));
my $pkey = $pem->read(
Filename => $keyfile,
Password => $pwd
);
$pem->write(
Content => $pkey,
Password => $pwd,
Filename => $keyfile
);
=head1 DESCRIPTION
I<Convert::PEM> reads and writes PEM files containing ASN.1-encoded
objects. The files can optionally be encrypted using a symmetric
cipher algorithm, such as 3DES. An unencrypted PEM file might look
something like this:
-----BEGIN DH PARAMETERS-----
MB4CGQDUoLoCULb9LsYm5+/WN992xxbiLQlEuIsCAQM=
-----END DH PARAMETERS-----
The string beginning C<MB4C...> is the Base64-encoded, ASN.1-encoded
"object."
An encrypted file would have headers describing the type of
encryption used, and the initialization vector:
-----BEGIN DH PARAMETERS-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,C814158661DC1449
AFAZFbnQNrGjZJ/ZemdVSoZa3HWujxZuvBHzHNoesxeyqqidFvnydA==
-----END DH PARAMETERS-----
The two headers (C<Proc-Type> and C<DEK-Info>) indicate information
about the type of encryption used, and the string starting with
C<AFAZ...> is the Base64-encoded, encrypted, ASN.1-encoded
contents of this "object."
The initialization vector (C<C814158661DC1449>) is chosen randomly.
=head1 USAGE
=head2 $pem = Convert::PEM->new( %arg )
Constructs a new I<Convert::PEM> object designed to read/write an
object of a specific type (given in I<%arg>, see below). Returns the
new object on success, C<undef> on failure (see I<ERROR HANDLING> for
details).
I<%arg> can contain:
=over 4
=item * Name
The name of the object; when decoding a PEM-encoded stream, the name
in the encoding will be checked against the value of I<Name>.
Similarly, when encoding an object, the value of I<Name> will be used
as the name of the object in the PEM-encoded content. For example, given
the string C<FOO BAR>, the output from I<encode> will start with a
header like:
-----BEGIN FOO BAR-----
I<Name> is a required argument.
=item * ASN
An ASN.1 description of the content to be either encoded or decoded.
I<ASN> is a required argument.
=item * Macro
If your ASN.1 description (in the I<ASN> parameter) includes more than
one ASN.1 macro definition, you will want to use the I<Macro> parameter
to specify which definition to use when encoding/decoding objects.
For example, if your ASN.1 description looks like this:
Foo ::= SEQUENCE {
x INTEGER,
bar Bar
}
Bar ::= INTEGER
If you want to encode/decode a C<Foo> object, you will need to tell
I<Convert::PEM> to use the C<Foo> macro definition by using the I<Macro>
parameter and setting the value to C<Foo>.
I<Macro> is an optional argument.
=back
=head2 $obj = $pem->decode(%args)
Decodes, and, optionally, decrypts a PEM file, returning the
object as decoded by I<Convert::ASN1>. The difference between this
method and I<read> is that I<read> reads the contents of a PEM file
on disk; this method expects you to pass the PEM contents as an
argument.
If an error occurs while reading the file or decrypting/decoding
the contents, the function returns I<undef>, and you should check
the error message using the I<errstr> method (below).
I<%args> can contain:
=over 4
=item * Content
The PEM contents.
=item * Password
The password with which the file contents were encrypted.
If the file is encrypted, this is a mandatory argument (well, it's
not strictly mandatory, but decryption isn't going to work without
it). Otherwise it's not necessary.
=back
=head2 $blob = $pem->encode(%args)
Constructs the contents for the PEM file from an object: ASN.1-encodes
the object, optionally encrypts those contents.
Returns I<undef> on failure (encryption failure, file-writing failure,
etc.); in this case you should check the error message using the
I<errstr> method (below). On success returns the constructed PEM string.
I<%args> can contain:
=over 4
=item * Content
A hash reference that will be passed to I<Convert::ASN1::encode>,
and which should correspond to the ASN.1 description you gave to the
I<new> method. The hash reference should have the exact same format
as that returned from the I<read> method.
This argument is mandatory.
=item * Password
A password used to encrypt the contents of the PEM file. This is an
optional argument; if not provided the contents will be unencrypted.
=back
=head2 $obj = $pem->read(%args)
Reads, decodes, and, optionally, decrypts a PEM file, returning
the object as decoded by I<Convert::ASN1>. This is implemented
as a wrapper around I<decode>, with the bonus of reading the PEM
file from disk for you.
If an error occurs while reading the file or decrypting/decoding
the contents, the function returns I<undef>, and you should check
the error message using the I<errstr> method (below).
In addition to the arguments that can be passed to the I<decode>
method (minus the I<Content> method), I<%args> can contain:
=over 4
=item * Filename
The location of the PEM file that you wish to read.
=back
=head2 $pem->write(%args)
Constructs the contents for the PEM file from an object: ASN.1-encodes
the object, optionally encrypts those contents; then writes the file
to disk. This is implemented as a wrapper around I<encode>, with the
bonus of writing the file to disk for you.
Returns I<undef> on failure (encryption failure, file-writing failure,
etc.); in this case you should check the error message using the
I<errstr> method (below). On success returns the constructed PEM string.
In addition to the arguments for I<encode>, I<%args> can contain:
=over 4
=item * Filename
The location on disk where you'd like the PEM file written.
=back
=head2 $pem->errstr
Returns the value of the last error that occurred. This should only
be considered meaningful when you've received I<undef> from one of
the functions above; in all other cases its relevance is undefined.
=head2 $pem->asn
Returns the I<Convert::ASN1> object used internally to decode and
encode ASN.1 representations. This is useful when you wish to
interact directly with that object; for example, if you need to
call I<configure> on that object to set the type of big-integer
class to be used when decoding/encoding big integers:
$pem->asn->configure( decode => { bigint => 'Math::Pari' },
encode => { bigint => 'Math::Pari' } );
=head1 ERROR HANDLING
If an error occurs in any of the above methods, the method will return
C<undef>. You should then call the method I<errstr> to determine the
source of the error:
$pem->errstr
In the case that you do not yet have a I<Convert::PEM> object (that is,
if an error occurs while creating a I<Convert::PEM> object), the error
can be obtained as a class method:
Convert::PEM->errstr
For example, if you try to decode an encrypted object, and you do not
give a passphrase to decrypt the object:
my $obj = $pem->read( Filename => "encrypted.pem" )
or die "Decryption failed: ", $pem->errstr;
=head1 AUTHOR & COPYRIGHTS
Benjamin Trott, ben@rhumba.pair.com
Except where otherwise noted, Convert::PEM is Copyright 2001
Benjamin Trott. All rights reserved. Convert::PEM is free
software; you may redistribute it and/or modify it under
the same terms as Perl itself.
=cut