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What is the "openssh-blacklist" package? Is it related to the Debians OpenSSL bug?
Yes it is related to the Debian OpenSSL "bug". It contains a list of of all DSA-1024 and RSA-2048 keys generated by a Debian sabotaged OpenSSL PRNG.
Using the ssh-vulnkey you can check private key against this database. E.g. to check your (ssh) private key use
$ ssh-vulnkey -v .ssh/id_rsa
For the server key
# ssh-vulnkey -v /etc/ssh/ssh_host_rsa_key
Required, but never shown