[openssl-users] ASN.1: Parsing a 'private' class

[Sec_Aficiondado]

Hi Massimiliano,

Please do share it here on the list. There might not be an immediate need for it, but you'll save a couple of days to the next poor soul that ventures down the same path :)

Your solution will be indexed and pop right up on search engines in the future.

Thanks!
Sent from my mobile

> On Aug 31, 2015, at 7:10 PM, Massimiliano Pala <director at openca.org> wrote:
> 
> Hi all,
> 
> I actually figured it out, if anybody is curious about the solution for parsing this CRYPTLIB signature envelope (in this case DSA) - write to me directly, I will be happy to share the solution.
> 
> Cheers,
> Max
> 
>> On 8/29/15 6:56 PM, Massimiliano Pala wrote:
>> Hi all,
>> 
>> I am trying to parse a sequence that has, after an integer, a 'private' (xclass) item. I was wondering what is the right templates / macros to be able to generate the ASN1 functions with the usual macro. An example of the structure I have to parse (B64 - DER), is the following:
>> 
>> MGICAQOAFGZKq8/wIYS7Iueq6NuaC3ESPqUKMAkGBSsOAwIaBQAwCwYHKoZIzjgEAQUABC8wLQIVAJTJ6W2QjBIbVQdAtLbPO3y1wazHAhRsXivNO/Eg4GMEgcmEx8OgsIxGzQ== 
>> 
>> [ you can paste it into http://www.lapo.it/asn1js/ to get useful info. ]
>> 
>> The field that is giving me issues is the 2nd field in the sequence - offest 5, length 20 (i.e., after SEQUENCE (2 bytes) + INTEGER (3 bytes) and then the 20bytes field that I want to parse). The type is 0x80 - context specific. By using the ASN1_get_object() function, I get the correct size (20), the tag (0), and the xclass (128). Now, how do I go in order to generate the useful ASN1 function with teh usual macros ? Here's an example (besides the second field) for what I am trying to do:
>> 
>> ASN1_SEQUENCE(TYPE) = {
>> 
>>    ASN1_SIMPLE(TYPE, field1, ASN1_INTEGER),
>> 
>>    XXXXXXX(TYPE, field2, YYYYY),                      <<-- What shall be used here ? What Macro ?
>> 
>>    ASN1_SEQUENCE_OF(TYPE, field3, ASN1_OBJECT),
>> 
>>    ASN1_SEQUENCE_OF(TYPE, field3, ASN1_OBJECT),
>> 
>>    ASN1_SIMPLE(TYPE, field3, ASN1_OCTET_STRING)       <<-- This might be wrong as well - just noticed it is a very
>> 
>> } ASN1_SEQUENCE_END(TYPE)                                    weird encoding (octet-string that encapsulates a sequence of integers)
>> 
>> 
>> Is there a way to have the macros do the work (e.g., shall I use other macros - template? - to define the field somehow) ? Or shall I just write my own d2i_ and i2d_ functions ?
>> 
>> Please let me know,
>> 
>> Cheers,
>> Max
>> 
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