captchas/captcha.sh

#!/bin/bash

# Copyright © 2021 Adrien Bourmault (neox@a-lec.org)
# Copyright © 2021 Echolib (echolib@dismail.de)

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.

# This script is an example captcha script.
# It takes the text to recognize in the captcha image as a parameter.
# It return the image binary as a result. ejabberd support PNG, JPEG and GIF.

# The whole idea of the captcha script is to let server admins adapt it to
# their own needs. The goal is to be able to make the captcha generation as
# unique as possible, to make the captcha challenge difficult to bypass by
# a bot.
# Server admins are thus supposed to write and use their own captcha generators.

# This script relies on ImageMagick.
# It is NOT compliant with ImageMagick forks like GraphicsMagick.

INPUT=$1
LENINPUT=${#INPUT}
DIGITS=(zéros uns deux trois quatres cinqs six septs huits neufs dix)
DIGIT=(zéro un deux trois quatre cinq six sept huit neuf dix)


# ****************************************************************************
# 
# Tools
#
# ****************************************************************************


# Loops 10 times (should be enough) to check if a TARGET number is in INPUT
GENERATE__NOTIN() {
for i in {1..10}
do
   FALSENBR=`seq 1 9 | sort -R | head -n 1`
   ! [[ $INPUT =~ $FALSENBR ]] \
      && break
done
}


# ****************************************************************************
#
# Captcha shapes
#
# ****************************************************************************


# REPLACEs a random number in INPUT by another one randomized
REPLACE() {
NAME="REPLACE"
PLACE=`seq 1 6 | sort -R | head -n 1`
TARGET=`echo "$INPUT" | head -c $PLACE | tail -c 1`

GENERATE__NOTIN
NAME+="-$FALSENBR-$TARGET"
NEWINPUT=${INPUT//$TARGET/$FALSENBR}
INSTRUCTIONS1="Recopiez ce nombre"
INSTRUCTIONS2="en changeant les ${DIGITS[FALSENBR]} en ${DIGITS[TARGET]}"
}


# REVERSEs INPUT. Ask to Add first or last number in random. 
REVERSE() {
NAME="REVERSE"
RFL=`seq 1 2 | sort -R | head -n 1` # Rand First (1) or Last (2)
ADDNBR=${DIGITS[ADDNBR]}

for ((i=$LENINPUT-1;i>=0;i--))
do
   NEWINPUT="$NEWINPUT${INPUT:$i:1}"
done

if (( $RFL == 1 ));then
   ADDNBR="${INPUT:0:1}"
   NAME+="_FIRST"
   NEWINPUT=${NEWINPUT:0:$LENINPUT-1} # Do not show first INPUT NBR
   INSTRUCTIONS1="Écrivez le chiffre ${DIGIT[$ADDNBR]} puis le nombre "
   INSTRUCTIONS2="en recopiant de DROITE à GAUCHE ←"
else
   ADDNBR="${INPUT:$LENINPUT-1:1}"
   NAME+="_LAST"
   NEWINPUT=${NEWINPUT:1:$LENINPUT-1} # Do not show last INPUT NBR
   INSTRUCTIONS1="Recopiez de DROITE à GAUCHE ←"
   INSTRUCTIONS2="et terminez par le chiffre ${DIGIT[$ADDNBR]}"
fi
NAME+="-$ADDNBR"
}


# Add FALSE NBR to INPUT at three randomized place
NOTIN() {
NAME="NOTIN"
GENERATE__NOTIN
PLACE=(`seq 0 $((LENINPUT-1)) | sort -R | head -n 3 | sort -n`)
for i in `seq 0 $((LENINPUT-1))`
do
   (( $i == ${PLACE[0]} )) \
      && NEWINPUT+="$FALSENBR"
   (( $i == ${PLACE[1]} )) \
      && NEWINPUT+="$FALSENBR"
   (( $i == ${PLACE[2]} )) \
      && NEWINPUT+="$FALSENBR"
   NEWINPUT="$NEWINPUT${INPUT:$i:1}"
done
NAME+="-$FALSENBR"
INSTRUCTIONS1="Recopiez ce nombre sans les ${DIGITS[FALSENBR]}"
}


# Take a random NBR from INPUT. Calculate X
CALCUL() {
PLACE=`seq 1 $((LENINPUT)) | sort -R | head -n 1`
TARGET=`echo "$INPUT" | head -c $PLACE | tail -c 1`
NEWINPUT=${INPUT//$TARGET/X}

RC=`seq 1 2 | sort -R | head -n 1` # 1 = - | 2 = +
if (( $RC == 1 ));then
   FALSENBR=`seq $TARGET 10 | sort -R | head -n 1`
   RESUME=$(( FALSENBR - TARGET ))
   INSTRUCTIONS1="Calculez: ${DIGIT[FALSENBR]} moins ${DIGIT[RESUME]} et copiez"
   NAME="CALCULM-$FALSENBR-$RESUME"
else
   FALSENBR=`seq 1 4 | sort -R | head -n 1`
   if (( $FALSENBR <= $TARGET ));then
      RESULT=$(( TARGET + FALSENBR ))
      RESUME=$(( TARGET - FALSENBR ))
      INSTRUCTIONS1="Calculez: ${DIGIT[FALSENBR]} plus ${DIGIT[RESUME]} et copiez"
      NAME="CALCULP-$FALSENBR-$RESUME"
   else
      RESULT=$(( FALSENBR - TARGET ))
      RESUME=$(( TARGET - RESULT ))
      INSTRUCTIONS1="Calculez: ${DIGIT[RESULT]} plus ${DIGIT[RESUME]} et copiez"
      NAME="CALCULP-$RESULT-$RESUME"
   fi
fi
INSTRUCTIONS2="en remplaçant chaque X par la somme"
}


# ****************************************************************************
#
# Random captcha shape choice (aka main)
#
# ****************************************************************************

MODULES=(CALCUL NOTIN REPLACE REVERSE)
RMODULE=`seq 0 $(( ${#MODULES[@]} - 1)) | sort -R | head -n 1`
eval "${MODULES[RMODULE]}"

TEXT="$NEWINPUT"
CHAPRILURI=/var/lib/ejabberd/chapril_captchas/$(date "+%Y-%m-%d-%H%M%S")_${NAME}_${INPUT}.png

convert -size 300x70 xc:none -pointsize 20 \
	\( -clone 0 -fill black \
	-stroke black -strokewidth 1 \
	-font Helvetica-Narrow  -annotate "0x0+0+0"     "\n $INSTRUCTIONS1" \
	-font Helvetica-Bold    -annotate  "0x0+0+22"   "\n   $TEXT" \
   -font Helvetica-Narrow  -annotate "0x0+0+44"    "\n $INSTRUCTIONS2" \
	-roll +$ROLL_X+0 \
	-wave "$WAVE1_AMPLITUDE"x"$WAVE1_LENGTH" \
	-roll -$ROLL_X+0 \) \
	-flatten -crop 300x70 +repage -quality 500 \
   -depth 11 png:"$CHAPRILURI"

convert -size 300x70 xc:none -pointsize 20 \
	\( -clone 0 -fill black \
	-stroke black -strokewidth 1 \
	-font Helvetica-Narrow  -annotate "0x0+0+0"  "\n $INSTRUCTIONS1" \
	-font Helvetica-Bold    -annotate "0x0+0+22" "\n   $TEXT" \
	-font Helvetica-Narrow  -annotate "0x0+0+44" "\n $INSTRUCTIONS2" \
	-roll +$ROLL_X+0 \
	-wave "$WAVE1_AMPLITUDE"x"$WAVE1_LENGTH" \
	-roll -$ROLL_X+0 \) \
	-flatten -crop 300x70 +repage -quality 500 -depth 11 png:-