ssss(1) 						      General Commands Manual							   ssss(1)

NAME

       ssss - Split and Combine Secrets using Shamir's Secret Sharing Scheme.

SYNOPSIS

       ssss-split -t threshold -n shares [-w token] [-s level] [-x] [-q] [-Q] [-D] [-v]

       ssss-combine -t threshold [-x] [-q] [-Q] [-D] [-v]

DESCRIPTION

       ssss  is an implementation of Shamir's Secret Sharing Scheme. The program suite does both: the generation of shares for a known secret, and
       the reconstruction of a secret using user-provided shares.

COMMANDS

       ssss-split: prompt the user for a secret and generate a set of corresponding shares.

       ssss-combine: read in a set of shares and reconstruct the secret.

OPTIONS

       -t threshold
	      Specify the number of shares necessary to reconstruct the secret.

       -n shares
	      Specify the number of shares to be generated.

       -w token
	      Text token to name shares in order to avoid confusion in case one utilizes secret sharing to protect  several  independent  secrets.
	      The generated shares are prefixed by these tokens.

       -s level
	      Enforce  the  scheme's  security	level  (in  bits). This option implies an upper bound for the length of the shared secret (shorter
	      secrets are padded). Only multiples of 8 in the range from 8 to 1024 are allowed. If this option is ommitted (or the value given	is
	      0) the security level is chosen automatically depending on the secret's length. The security level directly determines the length of
	      the shares.

       -x     Hex mode: use hexadecimal digits in place of ASCII characters for I/O. This is useful if one wants  to  protect  binary  data,  like
	      block cipher keys.

       -q     Quiet mode: disable all unnecessary output. Useful in scripts.

       -Q     Extra quiet mode: like -q, but also suppress warnings.

       -D     Disable the diffusion layer added in version 0.2. This option is needed when shares are combined that where generated with ssss ver-
	      sion 0.1.

       -v     Print version information.

EXAMPLE

       In case you want to protect your login password with a set of ten shares in such a way that any three of them can reconstruct the password,
       you simply run the command

       ssss-split -t 3 -n 10 -w passwd

       To reconstruct the password pass three of the generated shares (in any order) to

       ssss-combine -t 3

NOTES

       To  protect  a  secret  larger than 1024 bits a hybrid technique has to be applied: encrypt the secret with a block cipher and apply secret
       sharing to just the key. Among others openssl and gpg can do the encryption part:

       openssl bf -e < file.plain > file.encrypted

       gpg -c < file.plain > file.encrypted

SECURITY

       ssss tries to lock its virtual address space into RAM for privacy reasons. But this may fail  for  two  reasons:  either  the  current  uid
       doesn't	permit	page  locking, or the RLIMIT_MEMLOCK is set too low. After printing a warning message ssss will run even without obtaining
       the desired mlock.

AUTHOR

       This software (v0.5) was written in 2006 by B. Poettering (ssss AT point-at-infinity.org). Find the newest version of ssss on the project's
       homepage: http://point-at-infinity.org/ssss/.

FURTHER READING

       http://en.wikipedia.org/wiki/Secret_sharing

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