Added first draft of encrypted paper backup guide

how-to-create-encrypted-paper-backup/qr-restore.sh

@@ -0,0 +1,43 @@
+#! /bin/bash
+
+bold=$(tput bold)
+red=$(tput setaf 1)
+normal=$(tput sgr0)
+
+set -e
+
+printf "%s\n" "Scan QR code…"
+
+data=""
+
+while read line; do
+  if echo -n $line | grep -Eq "^QR-Code:"; then
+    line=$(echo -n $line | sed 's/QR-Code://')
+  fi
+  data="$data$line"
+  if [ "$line" = "-----END PGP MESSAGE-----" ]; then
+    killall zbarcam --signal SIGINT
+  else
+    data="$data\n"
+  fi
+done < <(zbarcam --nodisplay --quiet)
+
+encrypted_secret=$(echo -e $data)
+
+encrypted_secret_hash=$(echo -n "$encrypted_secret" | openssl dgst -sha512 | sed 's/^.* //')
+encrypted_secret_short_hash=$(echo -n "$encrypted_secret_hash" | head -c 8)
+
+printf "%s\n" "$encrypted_secret"
+printf "SHA512 hash: $bold%s$normal\n" "$encrypted_secret_hash"
+printf "SHA512 short hash: $bold%s$normal\n" "$encrypted_secret_short_hash"
+
+printf "$bold$red%s$normal\n" "Show secret? (y or n)? "
+
+read -r answer
+if [ "$answer" = "y" ]; then
+  secret=$(echo -e "$encrypted_secret" | gpg --decrypt)
+  gpg-connect-agent reloadagent /bye > /dev/null 2>&1
+  printf "Secret: $bold%s$normal\n" "$secret"
+fi
+
+printf "%s\n" "Done"