ssh-audit flagged some weak hashing algorithm which should be disabled about dropbear HOT 7 CLOSED

I used the same trick to disable those successfully. Thanks!

#define DROPBEAR_RSA_SHA1 0
#define DROPBEAR_DH_GROUP14_SHA1 0
#define DROPBEAR_SHA1_HMAC 0

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diffie-hellman-group14-sha1 and hmac-sha1 could probably be disabled imminently. Direct replacements diffie-hellman-group14-sha256 and hmac-sha2-256 were added in Dropbear 2018.76 and 2013.56 respectively, and ECDH methods were earlier too.

The bigger question would be when to disable ssh-rsa - Dropbear only added support for rsa-sha2 a year ago so it might be a bit premature to remove since people are still using older software. They are not long lived signatures, only during KEX.

To avoid a common confusion - once rsa-sha algorithm is removed, existing ssh-rsa hostkeys and authentication keys (authorized_keys) will still work. The client and server just use a different signature format ssh-sha2- internally. (ssh-agents might need upgrading too).

I don't think hmac-sha2-256 should be removed, Dropbear doesn't implement [email protected] which would be the higher preference. Since 2020.79 Dropbear's first preference cipher is [email protected] so the mac algorithm doesn't matter in that case.

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This fell of my RADAR... is it something you need do or are these command line switches I can try to disable?

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The others were dropped,ssh-rsa will be retired in a future release.

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@mkj - what are your thoughts on the other algorithms called out in the ssh-audit report?

# key exchange algorithms
(kex) diffie-hellman-group14-sha1    -- [warn] using weak hashing algorithm

# message authentication code algorithms
(mac) hmac-sha1                      -- [warn] using encrypt-and-MAC mode
                                     `- [warn] using weak hashing algorithm
                                     `- [info] available since OpenSSH 2.1.0, Dropbear SSH 0.28
(mac) hmac-sha2-256                  -- [warn] using encrypt-and-MAC mode
                                     `- [info] available since OpenSSH 5.9, Dropbear SSH 2013.56
# algorithm recommendations 
(rec) -diffie-hellman-group14-sha1   -- kex algorithm to remove 
(rec) -hmac-sha1                     -- mac algorithm to remove 
(rec) -hmac-sha2-256                 -- mac algorithm to remove 

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diffie-hellman-group14-sha1 and hmac-sha1 should eventually be disabled by default, probably at the same time as ssh-rsa with sha1.

I'm not intending to remove hmac-sha2-256. From what I can tell ssh-audit flags it because it has problems with CBC ciphers, but Dropbear disables those. [email protected] is a higher priority too.

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