Note: This page is quite old and is likely out of date. My opinions may have also changed dramatically since this was written. It is here as a reference until I get around to updating it.
Random Password Generation
This little ruby snippet generates a random 31 character string consisting of uppercase letters, lowercase letters, and numbers.
#!/usr/bin/env ruby character_set = [('a'..'z'),('A'..'Z'),(0..9)].map do |item| item.to_a end character_set.flatten! password = "" 31.times do password += character_set[rand(character_set.length)].to_s end puts password
Shamir's Secret Sharing Scheme
Citing from the Wikipedia article about Secret Sharing:
In cryptography, a secret sharing scheme is a method for distributing a secret amongst a group of participants, each of which is allocated a share of the secret. The secret can only be reconstructed when the shares are combined together; individual shares are of no use on their own. More formally, in a secret sharing scheme there is one dealer and n players. The dealer gives a secret to the players, but only when specific conditions are fulfilled. The dealer accomplishes this by giving each player a share in such a way that any group of t (for threshold) or more players can together reconstruct the secret but no group of less than t players can. Such a system is called a (t,n)-threshold scheme. A popular technique to implement threshold schemes uses polynomial interpolation ("Lagrange interpolation"). This method was invented by Adi Shamir in 1979. Note that Shamir's scheme is provable secure, that means: in a (t,n) scheme one can prove that it makes no difference whether an attacker has t-1 valid shares at his disposal or none at all; as long as he has less than t shares, there is no better option than guessing to find out the secret.
There is a fedora package named
ssss that can split a string up to 128
characters long into X pieces, requiring at least Y pieces to recover it.
Assuming the pieces are broken up over several different locations and stored
in different manners it's a fairly strong way to store passwords or other
information that needs to be written once and recovered rarely. The following
example uses X = 5, and Y = 3:
[root@localhost ~]# ssss-split -t 3 -n 5 Generating shares using a (3,5) scheme with dynamic security level. Enter the secret, at most 128 ASCII characters: my secret root password Using a 184 bit security level. 1-1c41ef496eccfbeba439714085df8437236298da8dd824 2-fbc74a03a50e14ab406c225afb5f45c40ae11976d2b665 3-fa1c3a9c6df8af0779c36de6c33f6e36e989d0e0b91309 4-468de7d6eb36674c9cf008c8e8fc8c566537ad6301eb9e 5-4756974923c0dce0a55f4774d09ca7a4865f64f56a4ee0
You make get the following error message as well which is safe to ignore as long as you're on a fully trusted system, and are the only user of such system.
WARNING: couldn't get memory lock (ENOMEM, try to adjust RLIMIT_MEMLOCK!).
To recover the example above, we need to tell it that we need 3 (being our Y) of the pieces to recover the password and it can be accomplished like so:
[root@localhost ~]# ssss-combine -t 3 Enter 3 shares separated by newlines: Share [1/3]: 3-fa1c3a9c6df8af0779c36de6c33f6e36e989d0e0b91309 Share [2/3]: 5-4756974923c0dce0a55f4774d09ca7a4865f64f56a4ee0 Share [3/3]: 2-fbc74a03a50e14ab406c225afb5f45c40ae11976d2b665 Resulting secret: my secret root password