NAME

       scrypt — encrypt and decrypt files.

SYNOPSIS

       scrypt   {enc  |  dec  |  info}  [-f]  [--logN  value]  [-M  maxmem]  [-m  maxmemfrac]  [-P]  [-p  value]
              [--passphrase method:arg] [-r value] [-t maxtime] [-v] 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.

       --logN value   Set  the  work  parameter N to 2^value.  If --logN is set, -r and -p must also be set.  If
                      such explicit parameters are given, the resource limits set by -M,  -m,  and  -t  are  not
                      enforced.

       -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.

       -P             Always  read passphrase from stdin, and do so only once even when encrypting.  This cannot
                      be used if infile is also stdin (aka '-').

       -p value       Set the work parameter p to value.  If -p is set, --logN and -r must also be set.  If such
                      explicit parameters are given, the resource limits set by -M, -m, and -t are not enforced.

       --passphrase method:arg
                      Read the passphrase using the specified method.

                      dev:tty-stdin
                          Attempt to read the passphrase from /dev/tty; if that fails, read it from stdin.  This
                          is the default behaviour.

                      dev:stdin-once
                          Attempt to read the passphrase from stdin, and do so only once even  when  encrypting.
                          This cannot be used if infile is also stdin (aka '-').

                      dev:tty-once
                          Attempt  to  read  the  passphrase  from  /dev/tty,  and  do  so  only  once even when
                          encrypting.

                      env:VAR
                          Read the passphrase from the environment variable specified by VAR.

                          Storing a passphrase in an environment variable may be a security risk.  Only use this
                          option if you are certain that you know what you are doing.

                      file:FILENAME
                          Read the passphrase from the file specified by FILENAME.

                          Storing a passphrase in a file may be a security risk.  Only use this  option  if  you
                          are certain that you know what you are doing.

       -r value       Set the work parameter r to value.  If -r is set, --logN and -p must also be set.  If such
                      explicit parameters are given, the resource limits set by -M, -m, and -t are not enforced.

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

       --v            Print encryption parameters (N, r, p) and memory/cpu limits.

       --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.

ALGORITHM PARAMETERS

       The  scrypt  algorithm  has three tuneable work parameters: N, r, p.  When decrypting, scrypt will always
       use the values specified by the encryption header.   When  encrypting,  scrypt  will  choose  appropriate
       values  based  on  your  system's  speed and memory (influenced by -M, -m, and/or -t), unless you specify
       explicit parameters via --logN, -p, -r.

SEE ALSO

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

       Colin Percival and Simon Josefsson, The scrypt Password-Based Key Derivation  Function,  IETF  RFC  7914,
       August 2016.

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)