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Perfect is the enemy of good enough.

Verifying a BIND source tarball using cryptographic signatures

Posted April 12, 2017 by shaun

When downloading and compiling software, it's always a good idea to verify the integrity of the source files you obtain. Package handlers like yum and apt handle this automatically, but it must be done manually when you download software yourself.

ISC, the publisher of the BIND DNS server, provides cryptographic signatures with each release. If you have gpg installed, you can use the signature to validate your downloaded BIND tarball. ISC's download URLs follow a consistent naming pattern; simply change the version number in the URLs below to match the version you need.

Download the BIND source

[root@host /home/files]# wget https://ftp.isc.org/isc/bind9/9.11.12/bind-9.11.12.tar.gz
  `bind-9.11.12.tar.gz' saved [8180761/8180761]

Download the associated signature file

[root@host /home/files]# wget https://ftp.isc.org/isc/bind9/9.11.12/bind-9.11.12.tar.gz.sha256.asc
  `bind-9.11.12.tar.gz.sha256.asc' saved [833/833]

Download ISC's PGP signing key

This is the PGP public key ISC will use for signing in 2019 and 2020. Prior and future keys will appear here.

[root@host /home/files]# wget https://ftp.isc.org/isc/pgpkeys/codesign2019.txt
  `codesign2019.txt' saved [16154/16154]

Import ISC's key to your gpg keyring

[root@host /home/files]# gpg --import codesign2019.txt
  gpg: key 4CBB3D38: public key "Internet Systems Consortium, Inc. 
       (Signing key, 2019-2020) <codesign@isc.org>" imported
  gpg: Total number processed: 1
  gpg:               imported: 1  (RSA: 1)
  gpg: no ultimately trusted keys found

Verify the tarball using the signature file

[root@host /home/files]# gpg --verify bind-9.11.12.tar.gz.sha256.asc bind-9.11.12.tar.gz
  gpg: Signature made Thu Oct  3 12:40:29 2019 CDT using RSA key ID 4CBB3D38
  gpg: Good signature from "Internet Systems Consortium, Inc. (Signing key, 2019-2020) <codesign@isc.org>"
  gpg: WARNING: This key is not certified with a trusted signature!
  gpg:          There is no indication that the signature belongs to the owner.
  Primary key fingerprint: AE3F AC79 6711 EC59 FC00  7AA4 74BB 6B9A 4CBB 3D38

The warning message displayed here can be safely ignored; it just means that you haven't personally marked ISC's key as trusted in your keyring. What you're looking for is the "Good signature" output, which is present here, indicating that the file you downloaded matches the one on the remote site.

Updated Oct 20, 2019 to reference BIND version 9.11.12.

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