Provided by: libconvert-ber-perl_1.3200-3_all 
NAME
Convert::BER - ASN.1 Basic Encoding Rules
SYNOPSIS
use Convert::BER;
$ber = new Convert::BER;
$ber->encode(
INTEGER => 1,
SEQUENCE => [
BOOLEAN => 0,
STRING => "Hello",
],
REAL => 3.7,
);
$ber->decode(
INTEGER => \$i,
SEQUENCE => [
BOOLEAN => \$b,
STRING => \$s,
],
REAL => \$r,
);
DESCRIPTION
WARNING this module is no longer supported, See Convert::ASN1
"Convert::BER" provides an OO interface to encoding and decoding data using the ASN.1
Basic Encoding Rules (BER), a platform independent way of encoding structured binary data
together with the structure.
METHODS
new
new ( BUFFER )
new ( opList )
"new" creates a new "Convert::BER" object.
encode ( opList )
Encode data in opList appending to the data in the buffer.
decode ( opList )
Decode the data in the buffer as described by opList, starting where the last decode
finished or position set by "pos".
buffer ( [ BUFFER ] )
Return the buffer contents. If BUFFER is specified set the buffer contents and reset
pos to zero.
pos ( [ POS ] )
Without any arguments "pos" returns the offset where the last decode finished, or the
last offset set by "pos". If POS is specified then POS will be where the next decode
starts.
tag ( )
Returns the tag at the current position in the buffer.
length ( )
Returns the length of the buffer.
error ( )
Returns the error message associated with the last method, if any. This value is not
automatically reset. If "encode" or "decode" returns undef, check this.
dump ( [ FH ] )
Dump the buffer to the filehandle "FH", or STDERR if not specified. The output
contains the hex dump of each element, and an ASN.1-like text representation of that
element.
hexdump ( [ FH ] )
Dump the buffer to the filehandle "FH", or STDERR if not specified. The output is hex
with the possibly-printable text alongside.
IO METHODS
read ( IO )
write ( IO )
recv ( SOCK )
send ( SOCK [, ADDR ] )
OPLIST
An opList is a list of operator-value pairs. An operator can be any of those defined
below, or any defined by sub-classing "Convert::BER", which will probably be derived from
the primitives given here.
The values depend on whether BER is being encoded or decoded:
Encoding
If the value is a scalar, just encode it. If the value is a reference to a list, then
encode each item in the list in turn. If the value is a code reference, then execute
the code. If the returned value is a scalar, encode that value. If the returned value
is a reference to a list, encode each item in the list in turn.
Decoding
If the value is a reference to a scalar, decode the value into the scalar. If the
value is a reference to a list, then decode all the items of this type into the list.
Note that there must be at least one item to decode, otherwise the decode will fail.
If the value is a code reference, then execute the code and decode the value into the
reference returned from the evaluated code.
PRIMITIVE OPERATORS
These operators encode and decode the basic primitive types defined by BER.
BOOLEAN
A BOOLEAN value is either true or false.
Encoding
The value is tested for boolean truth, and encoded appropriately.
# Encode a TRUE value
$ber->encode(
BOOLEAN => 1,
) or die;
Decoding
The decoded values will be either 1 or 0.
# Decode a boolean value into $bval
$ber->decode(
BOOLEAN => \$bval,
) or die;
INTEGER
An INTEGER value is either a positive whole number, or a negative whole number, or zero.
Numbers can either be native perl integers, or values of the "Math::BigInt" class.
Encoding
The value is the integer value to be encoded.
$ber->encode(
INTEGER => -123456,
) or die;
Decoding
The value will be the decoded integer value.
$ber->decode(
INTEGER => \$ival,
) or die;
STRING
This is an OCTET STRING, which is an arbitrarily long binary value.
Encoding
The value contains the binary value to be encoded.
$ber->encode(
STRING => "\xC0First character is hex C0",
) or die;
Decoding
The value will be the binary bytes.
$ber->decode(
STRING => \$sval,
) or die;
NULL
There is no value for NULL. You often use NULL in ASN.1 when you want to denote that
something else is absent rather than just not encoding the 'something else'.
Encoding
The values are ignored, but must be present.
$ber->encode(
NULL => undef,
) or die;
Decoding
Dummy values are stored in the returned values, as though they were present in the
encoding.
$ber->decode(
NULL => \$nval,
) or die;
OBJECT_ID
An OBJECT_ID value is an OBJECT IDENTIFIER (also called an OID). This is a hierarchically
structured value that is used in protocols to uniquely identify something. For example,
SNMP (the Simple Network Management Protocol) uses OIDs to denote the information being
requested, and LDAP (the Lightweight Directory Access Protocol, RFC 2251) uses OIDs to
denote each attribute in a directory entry.
Each level of the OID hierarchy is either zero or a positive integer.
Encoding
The value should be a dotted-decimal representation of the OID.
$ber->encode(
OBJECT_ID => '2.5.4.0', # LDAP objectClass
) or die;
Decoding
The value will be the dotted-decimal representation of the OID.
$ber->decode(
OBJECT_ID => \$oval,
) or die;
ENUM
The ENUMERATED type is effectively the same as the INTEGER type. It exists so that
friendly names can be assigned to certain integer values. To be useful, you should sub-
class this operator.
BIT_STRING
The BIT STRING type is an arbitrarily long string of bits - 0's and 1's.
Encoding
The value is a string of arbitrary 0 and 1 characters. As these are packed into 8-bit
octets when encoding and there may not be a multiple of 8 bits to be encoded, trailing
padding bits are added in the encoding.
$ber->encode(
BIT_STRING => '0011',
) or die;
Decoding
The value will be a string of 0 and 1 characters. The string will have the same number
of bits as were encoded (the padding bits are ignored.)
$ber->decode(
BIT_STRING => \$bval,
) or die;
BIT_STRING8
This is a variation of the BIT_STRING operator, which is optimized for writing bit strings
which are multiples of 8-bits in length. You can use the BIT_STRING operator to decode BER
encoded with the BIT_STRING8 operator (and vice-versa.)
Encoding
The value should be the packed bits to encode, not a string of 0 and 1 characters.
$ber->encode(
BIT_STRING8 => pack('B8', '10110101'),
) or die;
Decoding
The value will be the decoded packed bits.
$ber->decode(
BIT_STRING8 => \$bval,
) or die;
REAL
The REAL type encodes an floating-point number. It requires the POSIX module.
Encoding
The value should be the number to encode.
$ber->encode(
REAL => 3.14159265358979,
) or die;
Decoding
The value will be the decoded floating-point value.
$ber->decode(
REAL => \$rval,
);
ObjectDescriptor
The ObjectDescriptor type encodes an ObjectDescriptor string. It is a sub-class of
"STRING".
UTF8String
The UTF8String type encodes a string encoded in UTF-8. It is a sub-class of "STRING".
NumericString
The NumericString type encodes a NumericString, which is defined to only contain the
characters 0-9 and space. It is a sub-class of "STRING".
PrintableString
The PrintableString type encodes a PrintableString, which is defined to only contain the
characters A-Z, a-z, 0-9, space, and the punctuation characters ()-+=:',./?. It is a sub-
class of "STRING".
TeletexString/T61String
The TeletexString type encodes a TeletexString, which is a string containing characters
according to the T.61 character set. Each T.61 character may be one or more bytes wide. It
is a sub-class of "STRING".
T61String is an alternative name for TeletexString.
VideotexString
The VideotexString type encodes a VideotexString, which is a string. It is a sub-class of
"STRING".
IA5String
The IA5String type encodes an IA5String. IA5 (International Alphabet 5) is equivalent to
US-ASCII. It is a sub-class of "STRING".
UTCTime
The UTCTime type encodes a UTCTime value. Note this value only represents years using two
digits, so it is not recommended in Y2K-compliant applications. It is a sub-class of
"STRING".
UTCTime values must be strings like:
yymmddHHMM[SS]Z
or:
yymmddHHMM[SS]sHHMM
Where yy is the year, mm is the month (01-12), dd is the day (01-31), HH is the hour
(00-23), MM is the minutes (00-60). SS is the optional seconds (00-61).
The time is either terminated by the literal character Z, or a timezone offset. The "Z"
character indicates Zulu time or UTC. The timezone offset specifies the sign s, which is +
or -, and the difference in hours and minutes.
GeneralizedTime
The GeneralizedTime type encodes a GeneralizedTime value. Unlike "UTCTime" it represents
years using 4 digits, so is Y2K-compliant. It is a sub-class of "STRING".
GeneralizedTime values must be strings like:
yyyymmddHHMM[SS][.U][Z]
or:
yyyymmddHHMM[SS][.U]sHHMM
Where yyyy is the year, mm is the month (01-12), dd is the day (01-31), HH is the hour
(00-23), MM is the minutes (00-60). SS is the optional seconds (00-61). U is the optional
fractional seconds value; a comma is permitted instead of a dot before this value.
The time may be terminated by the literal character Z, or a timezone offset. The "Z"
character indicates Zulu time or UTC. The timezone offset specifies the sign s, which is +
or -, and the difference in hours and minutes. If there is timezone specified UTC is
assumed.
GraphicString
The GraphicString type encodes a GraphicString value. It is a sub-class of "STRING".
VisibleString/ISO646String
The VisibleString type encodes a VisibleString value, which is a value using the ISO646
character set. It is a sub-class of "STRING".
ISO646String is an alternative name for VisibleString.
GeneralString
The GeneralString type encodes a GeneralString value. It is a sub-class of "STRING".
UniversalString/CharacterString
The UniveralString type encodes a UniveralString value, which is a value using the
ISO10646 character set. Each character in ISO10646 is 4-bytes wide. It is a sub-class of
"STRING".
CharacterString is an alternative name for UniversalString.
BMPString
The BMPString type encodes a BMPString value, which is a value using the Unicode character
set. Each character in the Unicode character set is 2-bytes wide. It is a sub-class of
"STRING".
CONSTRUCTED OPERATORS
These operators are used to build constructed types, which contain values in different
types, like a C structure.
SEQUENCE
A SEQUENCE is a complex type that contains other types, a bit like a C structure. Elements
inside a SEQUENCE are encoded and decoded in the order given.
Encoding
The value should be a reference to an array containing another opList which defines
the elements inside the SEQUENCE.
$ber->encode(
SEQUENCE => [
INTEGER => 123,
BOOLEAN => [ 1, 0 ],
]
) or die;
Decoding
The value should a reference to an array that contains the opList which decodes the
contents of the SEQUENCE.
$ber->decode(
SEQUENCE => [
INTEGER => \$ival,
BOOLEAN => \@bvals,
]
) or die;
SET
A SET is an complex type that contains other types, rather like a SEQUENCE. Elements
inside a SET may be present in any order.
Encoding
The value is the same as for the SEQUENCE operator.
$ber->encode(
SET => [
INTEGER => 13,
STRING => 'Hello',
]
) or die;
Decoding
The value should be a reference to an equivalent opList to that used to encode the
SET. The ordering of the opList should not matter.
$ber->decode(
SET => [
STRING => \$sval,
INTEGER => \$ival,
]
) or die;
SEQUENCE_OF
A SEQUENCE_OF is an ordered list of other types.
Encoding
The value is a ref followed by an opList. The ref must be a reference to a list or a
hash: if it is to a list, then the opList will be repeated once for every element in
the list. If it is to a hash, then the opList will be repeated once for every key in
the hash (note that ordering of keys in a hash is not guaranteed by perl.)
The remaining opList will then usually contain values which are code references. If
the ref is to a list, then the contents of that item in the list are passed as the
only argument to the code reference. If the ref is to a hash, then only the key is
passed to the code.
@vals = ( [ 10, 'Foo' ], [ 20, 'Bar' ] ); # List of refs to lists
$ber->encode(
SEQUENCE_OF => [ \@vals,
SEQUENCE => [
INTEGER => sub { $_[0][0] }, # Passed a ref to the inner list
STRING => sub { $_[0][1] }, # Passed a ref to the inner list
]
]
) or die;
%hash = ( 40 => 'Baz', 30 => 'Bletch' ); # Just a hash
$ber->decode(
SEQUENCE_OF => [ \%hash,
SEQUENCE => [
INTEGER => sub { $_[0] }, # Passed the key
STRING => sub { $hash{$_[0]} }, # Passed the key
]
]
);
Decoding
The value must be a reference to a list containing a ref and an opList. The ref must
always be a reference to a scalar. Each value in the <opList> is usually a code
reference. The code referenced is called with the value of the ref (dereferenced); the
value of the ref is incremented for each item in the SEQUENCE_OF.
$ber->decode(
SEQUENCE_OF => [ \$count,
# In the following subs, make space at the end of an array, and
# return a reference to that newly created space.
SEQUENCE => [
INTEGER => sub { $ival[$_[0]] = undef; \$ival[-1] },
STRING => sub { $sval[$_[0]] = undef; \$sval[-1] },
]
]
) or die;
SET_OF
A SET_OF is an unordered list. This is treated in an identical way to a SEQUENCE_OF,
except that no ordering should be inferred from the list passed or returned.
SPECIAL OPERATORS
BER
It is sometimes useful to construct or deconstruct BER encodings in several pieces. The
BER operator lets you do this.
Encoding
The value should be another "Convert::BER" object, which will be inserted into the
buffer. If value is undefined then nothing is added.
$tmp->encode(
SEQUENCE => [
INTEGER => 20,
STRING => 'Foo',
]
);
$ber->encode(
BER => $tmp,
BOOLEAN => 1
);
Decoding
value should be a reference to a scalar, which will contain a "Convert::BER" object.
This object will contain the remainder of the current sequence or set being decoded.
# After this, ber2 will contain the encoded INTEGER B<and> STRING.
# sval will be ignored and left undefined, but bval will be decoded. The
# decode of ber2 will return the integer and string values.
$ber->decode(
SEQUENCE => [
BER => \$ber2,
STRING => \$sval,
],
BOOLEAN => \$bval,
);
$ber2->decode(
INTEGER => \$ival,
STRING => \$sval2,
);
ANY
This is like the "BER" operator except that when decoding only the next item is decoded
and placed into the "Convert::BER" object returned. There is no difference when encoding.
Decoding
value should be a reference to a scalar, which will contain a "Convert::BER" object.
This object will only contain the next single item in the current sequence being
decoded.
# After this, ber2 will decode further, and ival and sval
# will be decoded.
$ber->decode(
INTEGER = \$ival,
ANY => \$ber2,
STRING => \$sval,
);
OPTIONAL
This operator allows you to specify that an element is absent from the encoding.
Encoding
The value should be a reference to another list with another opList. If all of the
values of the inner opList are defined, the entire OPTIONAL value will be encoded,
otherwise it will be omitted.
$ber->encode(
SEQUENCE => [
INTEGER => 16, # Will be encoded
OPTIONAL => [
INTEGER => undef, # Will not be encoded
],
STRING => 'Foo', # Will be encoded
]
);
Decoding
The contents of value are decoded if possible, if not then decode continues at the
next operator-value pair.
$ber->decode(
SEQUENCE => [
INTEGER => \$ival1,
OPTIONAL => [
INTEGER => \$ival2,
],
STRING => \$sval,
]
);
CHOICE
The opList is a list of alternate operator-value pairs. Only one will be encoded, and only
one will be decoded.
Encoding
A scalar at the start of the opList identifies which opList alternative to use for
encoding the value. A value of 0 means the first one is used, 1 means the second one,
etc.
# Encode the BMPString alternate of the CHOICE
$ber->encode(
CHOICE => [ 2,
PrintableString => 'Printable',
TeletexString => 'Teletex/T61',
BMPString => 'BMP/Unicode',
UniversalString => 'Universal/ISO10646',
]
) or die;
Decoding
A reference to a scalar at the start of the opList is used to store which alternative
is decoded (0 for the first one, 1 for the second one, etc.) Pass undef instead of the
ref if you don't care about this, or you store all the alternate values in different
variables.
# Decode the above.
# Afterwards, $alt will be set to 2, $str will be set to 'BMP/Unicode'.
$ber->decode(
CHOICE => [ \$alt,
PrintableString => \$str,
TeletexString => \$str,
BMPString => \$str,
UniversalString => \$str,
]
) or die;
TAGS
In BER everything being encoded has a tag, a length, and a value. Normally the tag is
derived from the operator - so INTEGER has a different tag from a BOOLEAN, for instance.
In some applications it is necessary to change the tags used. For example, a SET may need
to contain two different INTEGER values. Tags may be changed in two ways, either
IMPLICITly or EXPLICITly. With IMPLICIT tagging, the new tag completely replaces the old
tag. With EXPLICIT tagging, the new tag is used as well as the old tag.
"Convert::BER" supports two ways of using IMPLICIT tagging. One method is to sub-class
"Convert::BER", which is described in the next section. For small applications or those
that think sub-classing is just too much then the operator may be passed an arrayref. The
array must contain two elements, the first is the usual operator name and the second is
the tag value to use, as shown below.
$ber->encode(
[ SEQUENCE => 0x34 ] => [
INTEGER => 10,
STRING => "A"
]
) or die;
This will encode a sequence, with a tag value of 0x34, which will contain and integer and
a string which will have their default tag values.
You may wish to construct your tags using some pre-defined functions such as
&Convert::BER::BER_APPLICATION, &Convert::BER::BER_CONTEXT, etc, instead of calculating
the tag values yourself.
To use EXPLICIT tagging, enclose the original element in a SEQUENCE, and just override the
SEQUENCE's tag as above. Don't forget to set the constructed bit using
&Convert::BER::BER_CONSTRUCTOR. For example, the ASN.1 definition:
Foo ::= SEQUENCE {
[0] EXPLICIT INTEGER,
INTEGER
}
might be encoded using this:
$ber->encode(
SEQUENCE => [
[ SEQUENCE => &Convert::BER::BER_CONTEXT |
&Convert::BER::BER_CONSTRUCTOR | 0 ] => [
INTEGER => 10,
],
INTEGER => 11,
],
) or die;
SUB-CLASSING
For large applications where operators with non default tags are used a lot the above
mechanism can be very error-prone. For this reason, "Convert::BER" may be sub-classed.
To do this the sub-class must call a static method "define". The arguments to "define" is
a list of arrayrefs. Each arrayref will define one new operator. Each arrayref contains
three values, the first is the name of the operator, the second is how the data is encoded
and the third is the tag value. To aid with the creation of these arguments "Convert::BER"
exports some variables and constant subroutines.
For each operator defined by "Convert::BER", or a "Convert::BER" sub-class, a scalar
variable with the same name is available for import, for example $INTEGER is available
from "Convert::BER". And any operators defined by a new sub-class will be available for
import from that class. One of these variables may be used as the second element of each
arrayref.
"Convert::BER" also exports some constant subroutines that can be used to create the tag
value. The subroutines exported are:
BER_BOOLEAN
BER_INTEGER
BER_BIT_STR
BER_OCTET_STR
BER_NULL
BER_OBJECT_ID
BER_SEQUENCE
BER_SET
BER_UNIVERSAL
BER_APPLICATION
BER_CONTEXT
BER_PRIVATE
BER_PRIMITIVE
BER_CONSTRUCTOR
"Convert::BER" also provides a subroutine called "ber_tag" to calculate an integer value
that will be used to represent a tag. For tags with values less than 30 this is not
needed, but for tags >= 30 then tag value passed for an operator definition must be the
result of "ber_tag"
"ber_tag" takes two arguments, the first is the tag class and the second is the tag value.
Using this information a sub-class of Convert::BER can be created as shown below.
package Net::LDAP::BER;
use Convert::BER qw(/^(\$|BER_)/);
use strict;
use vars qw($VERSION @ISA);
@ISA = qw(Convert::BER);
$VERSION = "1.00";
Net::LDAP::BER->define(
# Name Type Tag
########################################
[ REQ_UNBIND => $NULL,
BER_APPLICATION | 0x02 ],
[ REQ_COMPARE => $SEQUENCE,
BER_APPLICATION | BER_CONSTRUCTOR | 0x0E ],
[ REQ_ABANDON => $INTEGER,
ber_tag(BER_APPLICATION, 0x10) ],
);
This will create a new class "Net::LDAP::BER" which has three new operators available.
This class then may be used as follows
$ber = new Net::LDAP::BER;
$ber->encode(
REQ_UNBIND => 0,
REQ_COMPARE => [
REQ_ABANDON => 123,
]
);
$ber->decode(
REQ_UNBIND => \$var,
REQ_COMPARE => [
REQ_ABANDON => \$num,
]
);
Which will encode or decode the data using the formats and tags defined in the
"Net::LDAP::BER" sub-class. It also helps to make the code more readable.
DEFINING NEW PACKING OPERATORS
As well as defining new operators which inherit from existing operators it is also
possible to define a new operator and how data is encoded and decoded. The interface for
doing this is still changing but will be documented here when it is done. To be continued
...
LIMITATIONS
Convert::BER cannot support tags that contain more bits than can be stored in a scalar
variable, typically this is 32 bits.
Convert::BER cannot support items that have a packed length which cannot be stored in 32
bits.
BUGS
The "SET" decode method fails if the encoded order is different to the opList order.
AUTHOR
Graham Barr <gbarr@pobox.com>
Significant POD updates from Chris Ridd <Chris.Ridd@messagingdirect.com>
COPYRIGHT
Copyright (c) 1995-2000 Graham Barr. All rights reserved. This program is free software;
you can redistribute it and/or modify it under the same terms as Perl itself.