Some authentication/privacy combinations are not working correctly?

[anyn99]

Hi there!
I am in the process of implementing a SNMPv3 agent here at work.
For testing purposes i test our agent with net-snmp (v5.10-git@82862da) with OpenSSL-1.1.1.
And i also test against the pysnmp testserver demo.pysnmp.com. I actually do not know who is responsible for the testserver and what version it is...

While doing so i found that some authentication/privacy algorythms are maybe not working as expected?
I am interested in finding out why and how, also to make my own implementation better.
As far as i can tell the error could also be on the net-snmp side, but i am unsure.
Is anyone interested in working on this?

Here a table of all tested combinations:

pysnmp	0: None	1: DES	2: 3DES	3: AES128	4: AES192	4: AES192C	5: AES256	5: AES256C
0: None	OK	---	---	---	---	---	---	---
1: MD5	OK	OK	not supported	OK	Decryption error	OK	Decryption error	OK
2: SHA1	OK	OK	not supported	OK	Decryption error	OK	Decryption error	OK
3: SHA2-224	Decryption error	Decryption error	not supported	Decryption error	Decryption error	Decryption error	Decryption error	Decryption error
4: SHA2-256	OK	OK	not supported	OK	Decryption error	OK	Decryption error	OK
5: SHA2-384	OK	OK	not supported	OK	Decryption error	OK	Decryption error	OK
6: SHA2-512	Timeout!	Decryption error	not supported	Timeout!	Decryption error	Timeout!	Decryption error	Timeout!

legend:
"---": impossible combination
"not supported": net-snmp does not support 3DES, so it can't be tested
"Timeout": pysnmp is not sending anything after time syncronisation -> needs fix!
"Decryption error": pysnmp has sent an answer, but net-snmp couldn't decrypt -> those ones need fix

The "C" at the end of privacy algos is for "Cisco", which means key localization is done with reeder-draft.
Those without the "C" have key localization according to blumethal-draft.
While it seems that the reeder implementation is the "standard" for pysnmp, the blumenthal ones don't seem to work at a

[lextm]

You can read #429 first to gain some insights on the current ecosystem status.