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#!/usr/bin/env ruby
#!DESCRIBE: CLI based TOTP 2FA authenticator
require "openssl"
require "base32"
require "optimist"
def db32(str)
Base32.decode(str)
end
def hs1(key, counter, hsh = "sha1")
OpenSSL::HMAC.hexdigest(hsh, key.to_s, [counter].pack("Q>"))
end
def dt(str)
offset = str[-1].to_i(16)
p = str[(offset*2)...((offset+4)*2)]
p[0] = (p[0].to_i(16) & 0x7).to_s(16)
p.to_i(16)
end
def hotp(num, dig = 6)
num % (10 ** dig)
end
def fatal(msg)
$stderr.puts(msg)
exit 1
end
class Secrets
class Secret
def initialize(method, secret, tdc, dig, hsh)
@method = method
@secret = secret
@tdc = tdc
@dig = dig
@hsh = hsh
end
attr_reader :method
def verify(tx = Time.now.to_i)
case @method
when 'totp'
decoded = db32(@secret)
hmac = hs1(decoded, tx.to_i/@tdc.to_i, @hsh)
trunc = dt(hmac)
code = hotp(trunc, @dig)
"%0#{@dig}d" % code
when 'hotp'
decoded = db32(@secret)
hmac = hs1(decoded, @tdc, @hsh)
trunc = dt(hmac)
code = hotp(trunc, @dig)
@tdc += 1
"%0#{@dig}d" % code
else
fatal("I don't know how to #{@method}")
end
end
def time_remaining(tx = Time.now.to_i)
case @method
when 'totp'
(tx.to_i/@tdc.to_i + 1) * @tdc - tx
end
end
def puts
"#{@secret} #{@tdc} #{@dig} #{@hsh}"
end
end
def initialize(arr)
@secrets = {}
arr.each do |secretline|
m, i, s, tc, d, h = secretline.split
case m
when 'totp'
tc = tc&.to_i || 30
when 'hotp'
tc = tc&.to_i || 0
end
@secrets[i] = Secret.new(m, s, tc, d&.to_i || 6, h || "sha1")
end
end
def [](issuer)
@secrets[issuer]
end
def puts
@secrets.map do |i, s|
"#{s.method} #{i} #{s.puts}"
end
end
end
opts = Optimist::options do
version "twofa (c) 2019 Nat Lasseter"
banner <<-EOS
twofa is a command line OTP code generator.
Usage:
twofa [opts] ISSUER
where [opts] are:
EOS
opt :no_clip, "Do not copy code to the clipboard"
opt :twofa_file, "Location of the twofa secrets file",
type: :string, default: File.join(ENV["HOME"], ".twofa")
end
TWOFAFILE = opts[:twofa_file]
fatal("No 2fa issuers file at #{File.absolute_path(TWOFAFILE)}") unless File.exist?(TWOFAFILE)
SECRETS = Secrets.new(File.readlines(TWOFAFILE).map(&:strip))
ISSUER = ARGV.shift&.strip&.downcase
fatal("Specify issuer") if ISSUER.nil?
sec = SECRETS[ISSUER]
fatal("No such issuer") if sec.nil?
case sec.method
when 'totp'
code = sec.verify
time = sec.time_remaining
puts "#{code} (for #{time} more seconds)"
when 'hotp'
code = sec.verify
puts "#{code} (rolled counter)"
File.open(TWOFAFILE, ?w).puts SECRETS.puts
end
unless opts[:no_clip] then
require "clipboard"
Clipboard.copy(code)
puts "(Copied to clipboard)"
end
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