Dropbear 2020.79

Matt Johnston matt at ucc.asn.au
Mon Jun 15 23:52:51 AWST 2020

Hi all,

Dropbear 2020.79 is now released. Particular thanks to Vladislav Grishenko
for adding ed25519 and chacha20-poly1305 support which have
been wanted for a while.

This release also supports rsa-sha2 signatures which will be
required by OpenSSH in the near future - rsa with sha1 will
be disabled. This doesn't require any change to
hostkey/authorized_keys files.

Required versions of libtomcrypt and libtommath have been
increased, if the system library is older Dropbear can use
its own bundled copy.

As usual downloads are at


2020.79 - 15 June 2020

- Support ed25519 hostkeys and authorized_keys, many thanks to Vladislav Grishenko.
  This also replaces curve25519 with a TweetNaCl implementation that reduces code size.

- Add chacha20-poly1305 authenticated cipher. This will perform faster than AES
  on many platforms. Thanks to Vladislav Grishenko

- Support using rsa-sha2 signatures. No changes are needed to hostkeys/authorized_keys
  entries, existing RSA keys can be used with the new signature format (signatures
  are ephemeral within a session). Old ssh-rsa signatures will no longer
  be supported by OpenSSH in future so upgrading is recommended.

- Use getrandom() call on Linux to ensure sufficient entropy has been gathered at startup.
  Dropbear now avoids reading from the random source at startup, instead waiting until
  the first connection. It is possible that some platforms were running without enough 
  entropy previously, those could potentially block at first boot generating host keys.
  The dropbear "-R" option is one way to avoid that.

- Upgrade libtomcrypt to 1.18.2 and libtommath to 1.2.0, many thanks to Steffen Jaeckel for
  updating Dropbear to use the current API. Dropbear's configure script will check 
  for sufficient system library versions, otherwise using the bundled versions.

- CBC ciphers, 3DES, hmac-sha1-96, and x11 forwarding are now disabled by default.
  They can be set in localoptions.h if required.
  Blowfish has been removed.

- Support AES GCM, patch from Vladislav Grishenko. This is disabled by default,
  Dropbear doesn't currently use hardware accelerated AES.

- Added an API for specifying user public keys as an authorized_keys replacement.
  See pubkeyapi.h for details, thanks to Fabrizio Bertocci

- Fix idle detection clashing with keepalives, thanks to jcmathews

- Include IP addresses in more early exit messages making it easier for fail2ban
  processing. Patch from Kevin Darbyshire-Bryant

- scp fix for CVE-2018-20685 where a server could modify name of output files

- SSH_ORIGINAL_COMMAND is set for "dropbear -c" forced command too

- Fix writing key files on systems without hard links, from Matt Robinson

- Compatibility fixes for IRIX from Kazuo Kuroi

- Re-enable printing MOTD by default, was lost moving from options.h. Thanks to zciendor

- Call fsync() is called on parent directory when writing key files to ensure they are flushed

- Fix "make install" for manpages in out-of-tree builds, from Gabor Z. Papp

- Some notes are added in DEVELOPER.md

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