NAME

       scrypt — encrypt and decrypt files.

SYNOPSIS

       scrypt {enc | dec} [-f] [-M maxmem] [-m maxmemfrac] [-t maxtime] [-P] infile [outfile]
       scrypt --version

DESCRIPTION

       scrypt  enc  encrypts  infile  and  writes  the  result  to  outfile if specified, or the standard output
       otherwise.  The user will be prompted to enter a passphrase (twice) to be  used  to  generate  a  derived
       encryption key.

       scrypt  dec  decrypts  infile  and  writes  the  result  to  outfile if specified, or the standard output
       otherwise.  The user will be prompted to enter the passphrase used at encryption  time  to  generate  the
       derived encryption key.

       If  -P is not given, scrypt reads passphrases from its controlling terminal, or failing that, from stdin.
       Prompts are only printed when scrypt is reading passphrases from some terminal.  If  -P  is  given,  then
       scrypt does not print any prompts, and reads a passphrase from stdin.

OPTIONS

       -f             Force  the  decryption to proceed even if it is anticipated to require an excessive amount
                      of memory or CPU time.

       -M maxmem      Use at most maxmem bytes of RAM to compute the derived encryption key.

       -m maxmemfrac  Use at most the fraction maxmemfrac of the available RAM to compute the derived encryption
                      key.

       -t maxtime     Use at most maxtime seconds of CPU time to compute the derived encryption key.

       -P             Always read passphrase from stdin, and do so only once even when encrypting.

       --version      Print version of scrypt, and exit.

       In scrypt enc, the memory and CPU time limits are enforced  by  picking  appropriate  parameters  to  the
       scrypt  key  derivation  function.  In scrypt dec, the memory and CPU time limits are enforced by exiting
       with an error if decrypting the file would require too much memory or CPU time.

EXIT STATUS

       The scrypt utility exits 0 on success, and >0 if an error occurs.

       Note that if the input encrypted file is corrupted, scrypt dec may produce output  prior  to  determining
       that  the  input  was  corrupt and exiting with a non-zero status; so users should direct the output to a
       safe location and check the exit status of scrypt before using the decrypted data.

SEE ALSO

       Colin Percival, Stronger Key Derivation via Sequential Memory-Hard  Functions,  May  2009,  Presented  at
       BSDCan'09.

HISTORY

       The  scrypt  utility  was  written  in  May  2009  by Colin Percival as a demonstration of the scrypt key
       derivation function.  The scrypt key derivation function was invented in March 2009 by Colin Percival  in
       order to allow key files from the tarsnap backup system to be passphrase protected.

Debian                                               @DATE@                                            SCRYPT(1)