Hello, thanks for your answer. I think now i got it right.
Now that i have corrected the encoding of the restricted IA5String, it
seems that i have messed up a little more. The IA5String i have declared
earlier is part of an extension:
Let us assume the following:
mytype ::= SEQUENCE
{
a Type1,
...,
b SEQUENCE OF Type2 OPTIONAL
c Type3 OPTIONAL,
d Type3 OPTIONAL,
e Type3 OPTIONAL,
f Type3 OPTIONAL,
g Type3 OPTIONAL,
h Type3 OPTIONAL,
i Type3 OPTIONAL,
j Type3 OPTIONAL,
k Type3 OPTIONAL,
l Type3 OPTIONAL,
m Type3 OPTIONAL,
n Type3 OPTIONAL,
o Type3 OPTIONAL,
p Type3 OPTIONAL,
q Type3 OPTIONAL,
r Type3 OPTIONAL,
}
Type2 ::= CHOICE
{
mystring IA5String (SIZE (1..128)) (FROM ("01234567890#*,"),
c Type3
}
The encoding of the Sequence mytype seems to be correct up to the
extension marker (there are some more types, i left them out till
Ethereal shows me that encode them correctly). In the Extension Group
only b will be used, so the rest are dummy types to show the quantity.
Following i will show my understanding how the extension group should be
encoded with 1 item of type mystring = "55#12" in b.
First i have to encode the number of components in the extensions (which
is 16.
What about the extension flag? There should be a single 1 bit to show that
we'll be dealing with extensions.
In any case, I count 17, not 16, but the number of components you
show below is correct for 17.
0010000 Number of Components in extension
This is for 17. 0 represents 1, 1 represents 2, etc.
1. Item 0 (b) is used
00000000. No other Item is used
00000000.
OK, but when you include the extension flag as the first bit, you'll end
up with padding between here and the next field.
00000110. Byte Length of component b
Probably too large in light of the corrections below.
00000001. Items in Sequence of: 1
Yes.
00000000. Selection of Choice mystring (index 0)
Only 1 bit for the index. There are only two possibilities.
0000100x. Length of IA5String 5
1000 5
1000. 5
0000 #
0100. 1
0101 2
xxxx. padding
This part is OK, but that was yesterday's lesson!
In Hex
21 00 00 06 01 00 08 88 80 04 50
This is the Output of my encoding.
Ethereal say that the byte length of type b is 3 byte and tells that
mystring only consists of 5.
My guess that i have missencoded the length determinant in the extension
preamble. I have read again and again section 18 of X.691 but i didn't
find out what i have misunderstood.
So that we can be precise, let's define Type1 and Type3 as NULL. It
doesn't much matter what Type3 is, but Type1 is not OPTIONAL in your
example. In such a case, if we were to encode
m Mytype ::= { a NULL, b { mystring : "55#12" }}
we would see 90800000 05010488 0450 broken down as shown in the diagram
below. In my bit diagrams, x does not mean pad; it means
we-don't-care-about-this-bit-for-this-field.
Note that it will be easier to figure out the layout if you display this
email using a fixed font.
90 1001 0000
1xxx xxxx extension bit to denote that the data contains extensions
x001 0000 number of bits (17) in the extension bit mask
80 1000 0000
1xxx xxxx b is present
x0xx xxxx c is absent
xx0x xxxx d is absent
xxx0 xxxx e is absent
xxxx 0xxx f is absent
xxxx x0xx g is absent
xxxx xx0x h is absent
xxxx xxx0 i is absent
00 0000 0000
0xxx xxxx j is absent
x0xx xxxx k is absent
xx0x xxxx l is absent
xxx0 xxxx m is absent
xxxx 0xxx n is absent
xxxx x0xx o is absent
xxxx xx0x p is absent
xxxx xxx0 q is absent
00 0000 0000
0xxx xxxx r is absent
x000 0000 padding
05 0000 0101 length of b extension
01 0000 0001 number of iterations of the SEQUENCE OF
04 0000 0100
0xxx xxxx 0 = choice index for mystring
x000 0100 4 --> 5 length of mystring
88 1000 1000
1000 xxxx 5
xxxx 1000 5
04 0000 0100
0000 xxxx #
xxxx 0100 1
50 0101 0000
0101 xxxx 2
xxxx 0000 padding
=====================================================================
Conrad Sigona Voice Mail : 1-732-302-9669 x400
OSS Nokalva Fax : 1-614-388-4156
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