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mirleft / ocaml-asn1-combinators

Embed typed ASN.1 grammars in OCaml
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Integer with 0 length raises an exception #23

Closed emillon closed 4 years ago

emillon commented 5 years ago

Hi,

I'm using asn1-combinators to parse ECDSA signatures. The grammar is a sequence of two integers, ie sequence2 (required integer) (required integer).

Parsing the following byte string from project wycheproof causes an exception:

https://github.com/google/wycheproof/blob/c313761979d74b0417230eddd0f87d0cfab2b46b/testvectors/ecdsa_secp256r1_sha256_test.json#L943-L950

"invalid bounds in Cstruct.get_uint8 [4,0](39) off=0 len=1"

I expected a decode error to be returned (as Error _).

This can be reduced to the fact that parsing "02 00" as an integer raises the same error.

(interestingly, asn1js parses it as 0 in the structure, but returns an error when trying to parse 02 00 by itself)

Thanks!

pqwy commented 5 years ago

Thank you for the report!

I'm actually busily working on this. The fix itself is trivial (length field itself is not length checked here), but instead of playing whack-a-mole with individual fixes, I'm trying to get randomized testing to the point where it can actually recognize this as a bug.

I'm very happy you're running this over wycheproof corpus. Sadly, it is geared towards crypto primitives and uses relatively simple ASN grammars necessary for that. If there is a hand-curated corpus of more general ASN tests, especially negative tests, I would be ecstatic to know about it.

pqwy commented 5 years ago

Ok, this is handled here.

hannesm commented 4 years ago

thanks, this is fixed in 0.2.1 PRed to opam repository. closing.