Ubuntu Manpage: scrypt — encrypt and decrypt files

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.

     Unless otherwise specified via --passphrase, scrypt reads passphrases from its controlling
     terminal, or failing that, from stdin.  Prompts are only printed when scrypt is reading
     passphrases from some terminal.

OPTIONS

-f Force the operation to proceed even if it is anticipated to require an
excessive amount of memory or CPU time. Do not print any warnings about
exceeding any memory or CPU time limits.

--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. The maximum possible value for maxmemfrac is 0.5.

-P Deprecated synonym for --passphrase dev:stdin-once.

-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.

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.