tools: clean up lms_siglen.sh.

tools/lms/lms_siglen.sh

@@ -1,79 +1,59 @@
 #!/bin/bash
 #
 # Prints the LMS signature length given 3 LMS parameters.
-#
-# The total signature length is built up from several sub
-# signature lengths that need to be calculated.
-#
-# This assumes the LMS parameters are the same per each level
-# tree.
+# This assumes the LMS parameters are the same per each level tree.
 #
 # References:
-#   - https://datatracker.ietf.org/doc/html/rfc8554
-#   - https://github.com/cisco/hash-sigs
+#   - https://www.rfc-editor.org/info/rfc8554
 #   - https://eprint.iacr.org/2017/349.pdf
 
-# User parameters:
-#   levels = {1..8}
-#   height = {5, 10, 15, 20, 25}
-#   winternitz = {1, 2, 4, 8}
-levels=3
-height=5
-winternitz=8
-
-# Globals
-
-# The lm_pub_len is 4 less than the HSS pub len of 60.
-ots_sig_len=0
-sig_len=0
-total_len=0
-lm_pub_len=56
-
-# n and p.
-#  n == 32 by definition because this LMS implementation uses SHA256.
-#  p = f(w), it's a function of Winternitz value.
-n=32
-p=0
+print_usage_and_exit() {
+  echo "usage:"
+  echo "  ./lms_siglen.sh levels height winternitz"
+  echo ""
+  echo "options:"
+  echo "  levels = {1..8}"
+  echo "  height = {5, 10, 15, 20, 25}"
+  echo "  winternitz = {1, 2, 4, 8}"
+  exit 1
+}
 
-# Functions
+if [ $# -ne 3 ]; then
+  print_usage_and_exit
+fi
 
-# Get p given Winternitz value.
-ots_get_p() {
-  if [[ $winternitz == 1 ]]; then
-    p=265
-  else
-    p=$(((265 / winternitz) + 1))
-  fi
-}
+levels=$1
+height=$2
+winternitz=$3
 
-# Get the OTS sig len for given n and p.
-ots_get_sig_len() {
-  ots_sig_len=$((4 + n * (p + 1)))
-}
+if [[ $levels -lt 1 || $levels -gt 8 ]]; then
+  echo "error: invalid levels: $levels"; exit 1
+fi
 
-# Get the merkle tree sig len for given height and ots_sig_len.
-get_sig_len() {
-  sig_len=$((8 + $ots_sig_len + (n * $height)))
-}
+if [[ "$height" != @("5"|"10"|"15"|"20"|"25") ]]; then
+  echo "error: invalid height: $height"; exit 1
+fi
 
-# Finally, get the total signature length given the levels and sig_len.
-get_total_len() {
-  total_len=$((4 + (levels * sig_len) + ((levels - 1) * (lm_pub_len))))
-}
+if [[ "$winternitz" != @("1"|"2"|"4"|"8") ]]; then
+  echo "error: invalid winternitz: $height"; exit 1
+fi
 
-ots_get_p
-ots_get_sig_len
-get_sig_len
-get_total_len
+# n == 32 by definition because this LMS implementation uses SHA256.
+n=32
 
-echo "levels:      $levels"
-echo "height:      $height"
-echo "winternitz:  $winternitz"
-echo "#"
-# Extra debugging info
-# echo "n:           $n"
-# echo "p:           $p"
-# echo "#"
-# echo "ots_sig_len: $ots_sig_len"
-# echo "sig_len:     $sig_len"
-echo "total_len:   $total_len"
+# p = f(w). It's a function of Winternitz value.
+if [[ $winternitz == 1 ]]; then
+  p=265
+else
+  p=$(((265 / winternitz) + 1))
+fi
+
+# Get the signature length given parameters.
+# Reference: Table 2 of Kampanakis, Fluhrer, IACR, 2017.
+siglen=$((((36 * levels) + (2 * n * levels) - n - 20) + \
+            n * ((p * levels) + (height * levels))))
+
+echo "levels:     $levels"
+echo "height:     $height"
+echo "winternitz: $winternitz"
+echo "signature length: $siglen"