Tails is an operating system that boots off of removable media, either a DVD or a USB stick. For SecureDrop you'll need to install Tails onto USB sticks so that you can enable persistent storage.
The Tails website has detailed and up-to-date instructions on how to download and verify Tails, and how to create a Tails USB stick. Here are some links to help you out:
- Download, verify, install
- Installing onto a USB stick or SD card
- Create & configure the persistent volume
The tails documentation for "manually installing" Tails onto a USB device for Mac OS X include the following dd invocation to copy the .iso to the USB:
dd if=[tails.iso] of=/dev/diskX
This command is very slow (in our testing, it takes about 18 minutes to copy the .iso to a USB 2.0 drive). You can speed it up by adding the following arguments to dd:
dd if=[tails.iso] of=/dev/rdiskX bs=1m
Note the change from diskX to rdiskX. This reduced the copy time to 3 minutes for us. For an explanation, defer to the relevant Server Fault post ("I believe it has to do with buffers"). If you have GNU coreutils installed (such as through Homebrew), you may need to capitalize the M suffixed to the bs value.