[openssl-users] How to parse DER encoded x509 attributes?

[Dave Coombs]

Hello,

As I said, you could experiment with ASN1_TFLG_SET_OF instead of ASN1_TFLG_SEQUENCE_OF.

Also, to free the memory, you should be able to use just one call:
	sk_X509_ATTRIBUTE_pop_free(attrs, X509_ATTRIBUTE_free);

This frees each element in the stack, and also frees the stack.

All the best,
  -Dave


> On Nov 20, 2017, at 09:03, Libor Chocholaty <ossl at mts.cz> wrote:
> Hello,
> 
> thanks a lot. Works nice. Just it is interesting that I get X509_ATTRIBUTEs what should be a SEQUENCE but need to parse as SET.
> 
> And to free the memory:
> 
> X509_ATTRIBUTE *attr;
> while ((attr = sk_X509_ATTRIBUTE_pop(attrs)) != NULL) {
>     X509_ATTRIBUTE_free(attr);
> }
> sk_X509_ATTRIBUTE_free(attrs);
> 
> Looks working.
> 
> Regards,
> Libor
> 
>  
> On 2017-11-15 15:31, Dave Coombs wrote:
> 
>> Hello,
>>  
>> You can do something like the following.
>>  
>> First make a type corresponding to a stack of x509 attributes:
>>  
>>  typedef STACK_OF(X509_ATTRIBUTE) SEQ_X509_ATTRIBUTE;
>>  DECLARE_ASN1_FUNCTIONS(SEQ_X509_ATTRIBUTE);
>>  
>> Then make an asn1 template that specifies how the stack should be encoded.  (You can use ASN1_TFLG_SET_OF instead of ..SEQUENCE_OF here, depending on the DER you're trying to interpret, I don't know.)
>>  
>>  ASN1_ITEM_TEMPLATE(SEQ_X509_ATTRIBUTE) =
>>  ASN1_EX_TEMPLATE_TYPE(ASN1_TFLG_SEQUENCE_OF, 0, x509attribute, X509_ATTRIBUTE)
>>  ASN1_ITEM_TEMPLATE_END(SEQ_X509_ATTRIBUTE)
>>  IMPLEMENT_ASN1_FUNCTIONS(SEQ_X509_ATTRIBUTE)
>>  
>> Now your type has its own d2i and i2d functions, and you can use them:
>>  
>>  STACK_OF(X509_ATTRIBUTE) *attrs = d2i_SEQ_X509_ATTRIBUTE(NULL, &data, length);
>>  
>> Cheers,
>>   -Dave
>>  
>> 
>>> On Nov 15, 2017, at 07:26, Libor Chocholaty <ossl at mts.cz <mailto:ossl at mts.cz>> wrote:
>>> Hello,
>>> 
>>> I would like to parse DER encoded x509 attributes and have no clue how to use d2i_ASN1_SET_OF_X509_ATTRIBUTE. There are params that cannot find what to pass like free_func.
>>> 
>>> I am trying to uderstand by collecting pieces of known code, looking into openssl sources but...
>>> 
>>> PKCS7_SIGNER_INFO *p7si = PKCS7_SIGNER_INFO_new();
>>> d2i_ASN1_SET_OF_X509_ATTRIBUTE(&p7si->auth_attr, &der_data, der_data_length, d2i_X509_ATTRIBUTE, free_func, V_ASN1_SET, V_ASN1_UNIVERSAL);
>>> 
>>> Could somebody help how to do it or give a link to some useful documentation?
>>> Search internet looks completely not useful in this topic... or do not know how to ask...
>>> 
>>> Regards,
>>> Libor
>>> 
>>>  
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>>  
>  
>  
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