[aprssig] More secure passcodes for APRS-IS?

[Øyvind Hanssen]

I have observed some cases of abuse of the APRS-IS network. It is too 
easy to post disinformation or to do DOS attacks, etc. Also, everyone 
can read the APRS-IS data stream. Maybe there are local APRS-IS networks 
that need a more restrictive access policy?

The verification scheme is not designed to be secure. It is a simple 
hash of the username (callsign). Alternatively we might use SSL/TLS when 
making connections to APRS-IS nodes, but it is more complex to handle 
and not all software support it. It is necessary to have a CA that 
issues certificates, etc. etc. .

What about a more secure hashing scheme? Using a secret + the username 
to generate a hash. HMAC (possibly with SHA-256) is a de facto standard 
and more secure than a simple hashing scheme. Hashes can be truncated 
and base-64 encoded. If existing software can use e.g.  a 16 character 
code instead of the 4-digit (16bit) passcodes without modification, it 
may be something? Also, such a scheme does not encrypt content. If that 
is a requirement, maybe SSL/TLS is better.

It is not a proof of identity, but is a proof that you either know the 
secret or someone who does, has granted you access.  Only 
passcode-issuers and APRS-IS nodes need to know the secret. The risk is 
of course that the secret is leaked and it may be rather cumbersome if 
it must be renewed.

73

LA7ECA, Øyvind