a first cut

README.md

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+# Backup using Dump and GPG Encryption
+
+So you want to back up to a remote system, and you want it encrypted before it leaves the source system.  This hack uses classic UNIX `dump`; sorry for the brutality.  This example is also not incremental; your refund is in the post.  Let's assume the source system is Debian Linux.
+
+## Source Syatem backup User
+
+By default, both UNIX and Linux have a `backup` user, but with a strange directory etc.  So, on the source system, we will hack to instantiate the desired user.
+
+```
+sudo mkdir /home/backup
+sudo chown backup:backup /home/backup
+```
+
+Use `vipw` to configure `/home/backup` as the backup user's home directory.  It should look something similar to
+
+```
+backup:x:34:34:backup:/home/backup:/bin/bash
+```
+
+You may also want to configure the user so you are comfortable, i.e. add `.emacs` `.bashrc`, etc.
+
+You probably want your laptop's ssh public key to let you into the backup user account, so
+
+```
+sudo mkdir /home/backup/.ssh
+sudo chmod 700 /home/backup/.ssh
+sudo touch /home/backup/.ssh/authorised_keys
+sudo 600 chmod /home/backup/.ssh/authorised_keys
+sudo chown -Rbackup:backup /home/backup
+```
+
+and then somehow `cat` or copy your public key into `/home/backup/.ssh/authorised_keys`.
+
+Test that you can `ssh backup@source.host`
+
+You need to get the backup user so they can `sudo` without a passphrase.
+
+## The SSH Key
+
+For authenticating to the backup server and for transport encryption, you will want a separate ssh key for the purpose.
+
+SSH into the source host as the backup user
+
+
+```
+ssh-keygen -t ed25519
+```
+
+Agree to save the key pair in `/home/backup/.ssh/id_ed25519.
+
+Hit <enter> so no passphrase, and once again.
+
+Now take /home/backup/.ssh/id_ed25519.pub and give it to the sysadmin of the destination backup server.  They will install it in `/home/backup/.ssh/authorised_keys` on the backup server.
+
+Test that the backup user on the source system can ssh to the backup server.  You will have to accept that server's ssh host key.
+
+## Install dump
+
+If you will be using UNIX dump/restore, you need to install it.
+
+```
+sudo apt install dump
+```
+
+If you do not intend to back up entire filesystems, instead you could use tar or some equivalent.  For the moment, assume dump.
+
+## Generate the GPG Key Used for File Encryption
+
+As with the SSH key, you will want a separate GOG key for the file encryption.  It's simpler.  Again, as the backup user on the source host
+
+```
+gpg --gen-key
+```
+
+The real name might be yours, or maybe "Backup User".  Use your email address when asked.  Say OK.  To use a null passphrase, hit <enter> at the passphrase prompts.
+
+If you are on a VM, entropy is scarce, so it will hang forever.  There is a disgusting hack as follows:
+
+```
+sudo apt install haveged
+```
+
+and then have another go at GPG key generation.
+
+You will want to capture the key identity for later use.  So
+
+```
+gpg --list-keys
+```
+
+and there will be some long grotty key id such as `C6E74374512CD33FD1C2E47A7E84C28C1F64EAAF`.
+
+## The Script
+
+And now we wrap it all up in a grotty script
+
+```
+cat > do-dump << EOF
+gogs.sjc.arrcus.com:/home/backup> cat do-dump
+#!/bin/sh
+
+BSYS="raid0.sea.rg.net"
+USYS="backup@$BSYS"
+BDIR="/backup/arrcus"
+HOST=`hostname`
+DATE=`date "+%Y-%m-%d"`
+DDIR="$BDIR/$HOST.$DATE"
+DEST="$USYS:$DDIR"
+SSH="/usr/bin/ssh -i /home/backup/.ssh/id_ed25519"
+KEY_ID=C6E74374512CD33FD1C2E47A7E84C28C1F64EAAF
+GPG="/usr/bin/gpg --no-options --batch --no-greeting --no-secmem-warning --keyring /home/backup/.gnupg/pubring.kbx --secret-keyring /home/backup/.gnupg/secring.gpg --trustdb-name /home/backup/.gnupg/trustdb.gpg --digest-algo sha256 --cipher-algo aes256 --s2k-cipher-algo aes256 --s2k-digest-algo sha512 --encrypt --recipient $KEY_ID"
+
+# gogs.sjc.arrcus.com
+#
+# Filesystem      Size  Used Avail Use% Mounted on
+# /dev/vda1        61G  2.5G   56G   5% /
+
+$SSH $USYS mkdir $DDIR
+for F in base; do
+   $SSH $USYS touch $DDIR/$F
+   done
+
+sudo /sbin/dump -0uab 64 -f - / | $GPG | $SSH $USYS "/bin/cat > $DDIR/base"
+EOF
+```
+
+You probably will want to change
+* `BSYS` to whatever you have agreed with the target system's admin
+* `BDIR` wherever she told you you could stash your backups
+* `KEY_ID` to the GPG key from above
+
+And then modify the actual dumping details.
+
+---
+
+2020.01.06