DiceKeys looks very cool

[dragon788]

Hex dice only have 6 possible values for each position and don't have a lot of bits of entropy due to the limited sets of values. You could use something like Diceware to convert it to strings, but in that case it is a passphrase and not really a private key seed.

Using the Onerng is great if you have a device with a port to plug it into and open enough software to allow you to install a driver. If you only have an iPhone or Android and want to ensure there is no possible influence on the values due to buggy software/hardware implementations, using the DiceKeys gives you a random seed that can't be externally influenced and is stored safely outside of a computer or phone so that when those devices break (which is inevitable) you can still generate new secrets and decrypt old ones based on the physical seed.