https://github.com/xeals/signal-back
More information at the above link

Installation of precompiled binary for Signal-Back

wget https://github.com/xeals/signal-back/releases/download/v0.1.7-alpha.2/signal-back_linux_amd64
chmod +x signal-back_linux_amd64
./signal-back_linux_amd64

Help info

Usage: signal-back_linux_amd64 COMMAND [OPTION…] BACKUPFILE
   --help, -h     show help
   --version, -v  print the version
 Commands: 
   format   Read and format the backup file
   analyse  Information about the backup file
   extract  Retrieve attachments from the backup
   check    Verify that a backup is readable
   help     Shows a list of commands or help for one command

Extract attachments from backup

Replace ~/Desktop/signal…backup with the path to your Signal backup.

./signal-back_linux_amd64 extract ~/Desktop/signal-2019-09-30-01-43-21.backup

It’ll ask for the password and then start pulling out the attachments and putting them in the current directory.

Export messages to CSV file

Default option is XML. CSV will let you open it up in Excel.

./signal-back_linux_amd64 format -f CSV --output signal-output.csv ~/Desktop/signal-2019-09-30-01-43-21.backup

Specify password to use

You can use the -p option to specify the password. It does not matter if there are spaces every 5 numbers or not. Also the -P option is suppose to let you use a file.

./signal-back_linux_amd64 extract -p "48294 55709 09123 94563 74662 12800" ~/Desktop/signal-2019-09-30-01-43-21.backup

Other help options

bob@localhost:~/Downloads/signal-back$ ./signal-back_linux_amd64 help
 Usage: signal-back_linux_amd64 COMMAND [OPTION…] BACKUPFILE
 --help, -h     show help
   --version, -v  print the version
 Commands:
   format   Read and format the backup file
   analyse  Information about the backup file
   extract  Retrieve attachments from the backup
   check    Verify that a backup is readable
   help     Shows a list of commands or help for one command
bob@localhost:~/Downloads/signal-back$ ./signal-back_linux_amd64 help format
 Usage: signal-back_linux_amd64 format [OPTION…] BACKUPFILE
 Parse and transform the backup file into other formats.
 Valid formats include: CSV, XML, RAW.
 --format FORMAT, -f FORMAT  output the backup as FORMAT (default: "xml")
   --message TYPE, -m TYPE     format TYPE messages (default: "sms")
   --output FILE, -o FILE      write decrypted format to FILE
   --password PASS, -p PASS    use PASS as password for backup file
   --pwdfile FILE, -P FILE     read password from FILE
   --verbose, -v               enable verbose logging output
bob@localhost:~/Downloads/signal-back$ ./signal-back_linux_amd64 help extract
 Usage: signal-back_linux_amd64 extract [OPTION…] BACKUPFILE
 Decrypt files embedded in the backup.
 --outdir DIRECTORY, -o DIRECTORY  output attachments to DIRECTORY
   --password PASS, -p PASS          use PASS as password for backup file
   --pwdfile FILE, -P FILE           read password from FILE
   --verbose, -v                     enable verbose logging output
bob@localhost:~/Downloads/signal-back$