# find line starting with modulus:
#
while read line
do
 if [ "$line" = "modulus:" ]; then
  break
 fi
done

# extract modulus, up to line starting with publicExponent:
#
n=""
while read word rest
do
 if [ "$word" = "publicExponent:" ]; then break; fi
 n="$n$word" 
done

echo "n = $n" # debug

# n=$(echo "$n" | tr ...        # remove non-alphanumeric chars