scrypt-1.2.1/scrypt.1

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  24 .Dd February 10, 2017
  25 .Dt SCRYPT 1
  26 .Os
  27 .Sh NAME
  28 .Nm scrypt
  29 .Nd encrypt and decrypt files.
  30 .Sh SYNOPSIS
  31 .Nm
  32 .Brq Cm enc | Cm dec
  33 .Op Fl f
  34 .Op Fl M Ar maxmem
  35 .Op Fl m Ar maxmemfrac
  36 .Op Fl t Ar maxtime
  37 .Op Fl P
  38 .Ar infile
  39 .Op Ar outfile
  40 .Nm
  41 .Fl -version
  42 .Sh DESCRIPTION
  43 .Nm Cm enc
  44 encrypts
  45 .Ar infile
  46 and writes the result to
  47 .Ar outfile
  48 if specified, or the standard output otherwise.
  49 The user will be prompted to enter a passphrase (twice) to
  50 be used to generate a derived encryption key.
  51 .Pp
  52 .Nm Cm dec
  53 decrypts
  54 .Ar infile
  55 and writes the result to
  56 .Ar outfile
  57 if specified, or the standard output otherwise.
  58 The user will be prompted to enter the passphrase used at
  59 encryption time to generate the derived encryption key.
  60 .Pp
  61 If
  62 .Fl P
  63 is not given,
  64 .Nm
  65 reads passphrases from its controlling terminal, or failing that,
  66 from stdin.  Prompts are only printed when
  67 .Nm
  68 is reading passphrases from some terminal.  If
  69 .Fl P
  70 is given, then
  71 .Nm
  72 does not print any prompts, and reads a passphrase from stdin.
  73 .Sh OPTIONS
  74 .Bl -tag -width "-m maxmemfrac"
  75 .It Fl f
  76 Force the decryption to proceed even if it is anticipated to
  77 require an excessive amount of memory or CPU time.
  78 .It Fl M Ar maxmem
  79 Use at most
  80 .Ar maxmem
  81 bytes of RAM to compute the derived encryption key.
  82 .It Fl m Ar maxmemfrac
  83 Use at most the fraction
  84 .Ar maxmemfrac
  85 of the available RAM to compute the derived encryption key.
  86 .It Fl t Ar maxtime
  87 Use at most
  88 .Ar maxtime
  89 seconds of CPU time to compute the derived encryption key.
  90 .It Fl P
  91 Always read passphrase from stdin, and do so only once even
  92 when encrypting.
  93 .It Fl -version
  94 Print version of scrypt, and exit.
  95 .El
  96 .Pp
  97 In
  98 .Nm Cm enc ,
  99 the memory and CPU time limits are enforced by picking
 100 appropriate parameters to the
 101 .Nm
 102 key derivation function.
 103 In
 104 .Nm Cm dec ,
 105 the memory and CPU time limits are enforced by exiting with
 106 an error if decrypting the file would require too much memory
 107 or CPU time.
 108 .Sh EXIT STATUS
 109 The
 110 .Nm
 111 utility exits 0 on success, and >0 if an error occurs.
 112 .Pp
 113 Note that if the input encrypted file is corrupted,
 114 .Nm Cm dec
 115 may produce output prior to determining that the input
 116 was corrupt and exiting with a non-zero status; so
 117 users should direct the output to a safe location and
 118 check the exit status of
 119 .Nm
 120 before using the decrypted data.
 121 .Sh SEE ALSO
 122 .Rs
 123 .%A "Colin Percival"
 124 .%T "Stronger Key Derivation via Sequential Memory-Hard Functions"
 125 .%O "Presented at BSDCan'09"
 126 .%D "May 2009"
 127 .Re
 128 .Sh HISTORY
 129 The
 130 .Nm
 131 utility was written in May 2009 by Colin Percival as a
 132 demonstration of the
 133 .Nm
 134 key derivation function.
 135 The
 136 .Nm
 137 key derivation function was invented in March 2009 by Colin
 138 Percival in order to allow key files from the
 139 .Nm tarsnap
 140 backup system to be passphrase protected.