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.