Last Call Review of draft-ietf-opsawg-tacacs-13
review-ietf-opsawg-tacacs-13-secdir-lc-salowey-2019-04-21-00

As the draft mentions the MD5 based stream cipher used by TACACS+ is 
completely insecure.  I think there is too much discussion in the security
considerations that may lead one to think that in some cases it provides
sufficient protection.

Section 10.1 -
There have been plenty of analysis of the problems with the TACACS+ message
protection.  This section should just simply say the encryption/obfuscation
mechanism provides no integrity protection, no privacy protection and no replay
protection.  An attacker with access to the data stream should be assumed to be
able to read and modify all TACACS+ packets.  There are just too many flaws to
to enumerate in this document and the rest of the information in this section
is wrong or incomplete at best.

Section 10.2 -
Why not MUST NOT for TAC_PLUS_AUTHEN_STATUS_FOLLOW?  Is this really still used?

Section 10.2, 10.3, 10.4 -
You can probably replace most of these sections with
"TACACS+ MUST be used with an addition security mechanism to protection of the
communication such as IPSEC or a secure network such as described in 10.5. "

Section 10.5.1 and 10.5.2 -
Why should I care about secrets if they are just providing obfuscation?   Are
you relying on these secrets for something other than obfuscation?

Section 10.5.3 -
Use "less weak" instead of stronger when referring to CHAP, MS-CHAP, and
MSCHAPv2.   Its pretty debatable how much better they are than plaintext
passwords.