Hello Banibrata, see below. Bruno Konik - uniGone
_____ De : [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] De la part de Dutta, Banibrata (STSD) Envoyé : lundi 5 mars 2007 15:35 À : [email protected] Objet : [Asn1] Confusion about OID BER encoding (again) Hi, About 10-11 months back I'd posted the question regarding BER encoding of OID's, and now I am back, since some doubts are. How do I decode the following octet string, using the explanation of the encoding rules as specified in X.690. 06 0c 2a 86 3a 00 89 61 33 01 00 01 00 01 I'll write here, how far I manage to do it... Tag = 0x06 Length = 0xc (12), count of folliowing value octets Value = { 2a = 1.2. 86 = 6. 3a = 58. 00 = 0. 89 = (10001001)2 ??? (I thought that the MSbit could be one, only for the terminal octet!!) 61 = (01100001)2 ? (.. so is this octet related to the previous one, the one above in this list ? if so, how ?) The MSBit is 1 for the first octets and 0 for the last one which indicates the end of the encoding for that particular arc (integer encoded on 7 bits). O. Dubuisson's book is clear about this (I quote 18.2.8) : The encoding is always in primitive form. It is the number associated with each arc that is encoded but not the ident iers. Every integer is encoded on a series of octets where all the bits no. 7 but for the last octet equals 1. The encoding of the integer is therefore the concatenation of the bits from no. 6 down to no. 0 for each octet (this form is similar to the long-form encoding of the tag octets presented in Figure 18.2 on page 396). 33 = 51. ?? 01 = 1. ?? 00 = 0. ?? 01 = 1. ?? 00 = 0. ?? 01 = 1. ?? } I think this list doesn't permit HTML formatting, which is sad, because I'd colour coded the text to explain the issue in more clear terms. To me the problem is in the octet's with value 89 onwards... since it has the MSBit set. According to the explanation in X.690 & Olivier Dubuisson's books, the MSBit = 1, would occur only once ??? (Or, that's what I understood). Thanks for clarifying this issue. regards, Banibrata Dutta Hewlett-Packard | [EMAIL PROTECTED] | Å +91 80 22051796 | ü GMT +5.5
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