#! /bin/sh
###
### Reveal shares of a secret distributed among keepers
###
### (c) 2011 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This file is part of the distorted.org.uk key management suite.
###
### distorted-keys is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### distorted-keys is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with distorted-keys; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

set -e
case "${KEYSLIB+t}" in t) ;; *) echo >&2 "$0: KEYSLIB unset"; exit 1 ;; esac
. "$KEYSLIB"/keyfunc.sh

defhelp <<HELP
RECOV KEEPER [KEY]
Reveal a share of a recovery key distributed among keepers.

If enough shares have been revealed, reconstruct the recovery private key.
The key is read from KEY, or stdin if KEY is omitted or \`-'.
HELP
dohelp

## Parse the command line.
case $# in
  2) if [ -t 0 ]; then echo >&2 "$quis: stdin is a terminal"; exit 1; fi ;;
  3) ;;
  *) echo >&2 "$usage"; exit 1 ;;
esac
recov=$1 keeper=$2; shift 2
checklabel "recovery key" "$recov"
case "$recov" in
  */*) ;;
  *) recov=$recov/current ;;
esac
checkword "keeper set label" "$keeper"

## Grab the key, because we'll need to read it several times.
tmp=$(mktmp); cleanup rmtmp
secret=$(cat -- "$@")
pub=$(ec_public /dev/stdin <<EOF
$secret
EOF
)

## Read the threshold from the recovery metadata.
read param <$KEYS/recov/$recov/$keeper.param
case "$param" in
  shamir-params:*) ;;
  *)
    echo >&2 "$quis: secret sharing parameter file damaged (wrong header)"
    exit 1
    ;;
esac
t=";${param#*:}"
case "$t" in
  *";t="*) ;;
  *)
    echo >&2 "$quis: secret sharing parameter file damaged (missing t)"
    exit 1
    ;;
esac
t=${t#*;t=}
t=${t%%;*}

## Find out which keeper index it corresponds to.
read n hunoz <$KEYS/keeper/$keeper/meta
i=0
foundp=nil
: "$pub"
while [ $i -lt $n ]; do
  read cand <$KEYS/keeper/$keeper/$i.pub
  : "$cand"
  case "$pub" in "$cand") foundp=t; break ;; esac
  i=$(( i + 1 ))
done
case $foundp in
  nil) echo >&2 "$quis: key doesn't match keeper \`$keeper'"; exit 1 ;;
esac

## Establish the recovery staging area.  See whether we've done enough
## already.
mem=$(userv root claim-mem-dir </dev/null)
tag=$(echo $recov | tr / .)
mkdir -p -m700 $mem/keys.reveal
reveal=$mem/keys.reveal/$tag
if [ ! -d $reveal ]; then mkdir -m700 $reveal; fi
cd $reveal
if [ -f secret ]; then
  echo >&2 "$quis: secret $recov already revealed"
  exit 1
fi
if [ -f $keeper.$i ]; then
  echo >&2 "$quis: share $i already revealed"
  exit 1
fi

## Decrypt the share.
umask 077
ec_decrypt /dev/stdin \
  -i$KEYS/recov/$recov/$keeper.$i.share \
  -o$keeper.$i.new <<EOF
$secret
EOF
mv $keeper.$i.new $keeper.$i

## See if there's enough for a recovery.
n=0
for j in $keeper.*; do if [ -f "$j" ]; then n=$(( n + 1 )); fi; done
if [ $n -lt $t ]; then
  echo >&2 "$quis: share $i revealed; $(( t - n )) more required"
else
  cat $KEYS/recov/$recov/$keeper.param $keeper.* >$keeper.shares
  shamir recover <$keeper.shares >secret.new
  pubx=$(ec_public secret.new)
  puby=$(cat $KEYS/recov/$recov/pub)
  case "$pubx" in
    "$puby") ;;
    *)
      echo >&2 "quis: recovered secret key doesn't match public key"
      exit 1
      ;;
  esac
  mv secret.new secret
  echo >&2 "$quis: secret $recov revealed"
fi

###----- That's all, folks --------------------------------------------------