Greetings,
How can I simply encode some binary data into an ASN.1 DER-encoded blob? I’m using C/C++, and I figure it should be possible to simply prefix the binary blob with some appropriate bytes that signify that the data is of type octet string and is of a given length (and in a sequence of length 1 I guess).
Background if you’re interested:
Why do I want to abuse ASN.1 in this way? For a research project, I need to embed some data in a digital signature that has an associated an X.509 certificate. (I’m using createSignatureEx in Peter Gutmann’s cryptlib library to create CMS / S/MIME-2/3 / PKCS-#7 compliant signatures if it matters. I’m not signing the data I want to encode, just adding it as metadata to the signature to enrich it.) According to my understanding, serious signatures with arbitrary extension data require the extension data to be encoded using ASN.1 DER. My data is a binary blob and is only useful to my application, so there’s no real value in doing proper ASN.1 encoding of each part of my data. I figure with some work I could learn to use asn1c to do this, but it looks pretty complicated and I’m on deadline. Equally importantly, it seems unnecessary and it seems like this information could be useful to other developers who want to avoid the pain of proper ASN.1 encoding.
Thanks!
I would use the ASN.1 Compiler.
People abuse ASN.1 because it is a way to encode data structures. Any time you have a C/C++ program working with a data structure that the attacker controls problems like; buffer overflows and integer overflows, come into play. ASN.1 is no more insecure than lets say XML or JSON or bencode, as these are all likely points of failure. There can be problems with the encoding library its self, like this nasty Microsoft vulnerability. But this statement is true regardless of the encoding method you use. ASN.1 is a great choice because the resulting message is extremely small and it is the most efficient use of space of any encoding method that I know of.