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.