How to encode [0] IMPLICIT SET OF? about libtomcrypt HOT 3 OPEN

It's possible that this currently can't be done with any ltc version.

Can you provide an example "CMS SignedData certificate" in encoded format (i.e. the expected output)?

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The CMS spec RFC 5652 uses a CONTEXT SENSITIVE [0] IMPLICIT SET OF for the certificates member of a SignedData structure. A second example in CMS is the signedAttrs member of a SignerInfo structure.

But, maybe a toy example will be more useful here. In the example below, the integers are sorted by their DER encoding. This is implemented in der_encode_setof() but it isn't called from der_encode_custom_type().

Toy ::= SEQUENCE {
  hello        UTF8String,
  numbers [0]  IMPLICIT SET OF Number  }

Number ::= INTEGER { zero(0), one(1) }

30 0F 
  0C 02 68 69 
  A0 09 
    02 01 00
    02 01 00
    02 01 01

When the data type LTC_ASN1_CUSTOM_TYPE represents a primitive ASN.1 data type, the member used indicates the structure of the data member. Maybe that API could work also for a constructed ASN.1 data type, to distinguish SEQUENCE, SET and SET OF.

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The function der_encode_set() overwrites the member ltc_asn1_list.used, then passes the list to the function der_encode_sequence_ex(). Maybe der_encode_set() should use the member ltc_asn1_list.optional instead for set ordering.

It wouldn't be a bad idea to modify ltc_asn1_list to use an anonymous union to rename the members used and optional (for decoding) to custom_type and set_order (for encoding).

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