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.\"                                      Hey, EMACS: -*- nroff -*-
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.\" First parameter, NAME, should be all caps
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.\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
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.\" other parameters are allowed: see man(7), man(1)
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.TH NETTLE\-PBKDF2 1 "June 2014" "Nettle 3.0"  "Nettle tools"
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.\" Please adjust this date whenever revising the manpage.
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.SH NAME
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nettle\-pbkdf2 \- Command-line password-based key derivation tool.
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.SH SYNOPSIS
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.B nettle\-pbkdf2
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.RI [ OPTIONS ]
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.I SALT
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.SH DESCRIPTION
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This manual page documents briefly the
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.B nettle\-pbkdf2
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command.
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This manual page was written for the Debian GNU/Linux distribution
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because the original program does not have a manual page.
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.PP
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.\" TeX users may be more comfortable with the \fB<whatever>\fP and
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.\" \fI<whatever>\fP escape sequences to invode bold face and italics,
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.\" respectively.
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\fBnettle\-pbkdf2\fP is a front-end for Nettle's PBKDF2
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(Password-Based Key Derivation Function 2) implementation. PBKDF2
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applies a pseudo-random function to a passphrase together with a salt,
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producing a \fIderived key\fP of arbitrary length. By iterating the
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process many times, feeding the output of each round as the input of
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the next, brute-force cracking of the password is made to take
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correspondingly longer time. The use of a salt makes it harder to use
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dictionaries or rainbow tables. As computers become more powerful, the
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number of iterations can be increased without changing the rest of the
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algorithm.
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.PP
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The pseudo-random function used by this tool is currently HMAC-SHA256.
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.PP
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The password is read from standard input and the resulting derived key
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is written to standard output in groups of 16 hexadecimal digits,
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unless the \-\-raw option is used. The salt and number of iterations
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are not included in the output.
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.SH OPTIONS
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This program follows the usual GNU command line syntax, with long
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options starting with two dashes (`-').  A summary of options is
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included below.
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.TP
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.B \-l, \-\-length=\fIlength\fP
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Desired output length in octets.
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.TP
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.B \-\-raw
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Output derived key in raw binary format.
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.TP
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.B \-\-hex-salt
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Specifies that \fISALT\fP is provided in hexadecimal format.
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.TP
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.B \-\-help
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Show summary of options.
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.TP
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.B \-V, \-\-version
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Show version of program.
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.SH SEE ALSO
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.BR mkpasswd (1) ,
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.IR https://en.wikipedia.org/wiki/PBKDF2
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.SH AUTHOR
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This manual page was originally written by Magnus Holmgren <holmgren@debian.org>,
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for the Debian GNU/Linux system (but may be used by others).