NAME

       scrypt — encrypt and decrypt files.

SYNOPSIS

       scrypt {enc | dec | info} [-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.

       scrypt info provides information about the encryption parameters used for infile.

       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.  This  cannot
                      be used if infile is also stdin (aka '-').

       --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)