From 2edfa57eaaf12e65131d2a081ffd2382319c3c7f Mon Sep 17 00:00:00 2001
From: Dirk Wetter <dirk@testssl.sh>
Date: Tue, 19 Oct 2021 19:42:12 +0200
Subject: [PATCH] Check cert serial len + fix output when too big

OpenSSL shows certificate serial numbers >35 with a LF (0A). Testssl.sh
just output that which makes JSON invalid and displays the LF in the terminal
too.

This commit fixes that (#2010) by adding filters so that the
serialnumber is not a multiline string.

Also this commit introduces a new function: a size check of the cert serial.
Below 8 bytes the CAB Forum's lower limit is hit which says the *entropy*
from a CSPRNG should be at least 64 bits. It is assumed that below 8 bytes
length this requirement isn't possible to meet (needs to be clarified with
Shannon, 8 bytes seems to low to me).
  The high threshold is according to RFC 5280, Section-4.1.2.2 .

See also #2013.

The output has changed, so that on the terminal the serial has one line,
SHA1 and SHA256 each one line. The new json key is "cert_serialNumberLen".
---
 testssl.sh | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/testssl.sh b/testssl.sh
index 0b6e4fd..6f9e3c7 100755
--- a/testssl.sh
+++ b/testssl.sh
@@ -8429,8 +8429,10 @@ certificate_transparency() {
      return 0
 }
 
-# replacement for inline $OPENSSL x509 -noout -in $HOSTCERT -serial
-#                   and  $OPENSSL x509 -noout -in $HOSTCERT -fingerprint -sha256/-sha1
+# Shortcut for $OPENSSL x509 -noout -in $cert $ossl_command
+# arg1 is the certificate
+# arg2 is -serial | -fingerprint -sha1 | -fingerprint -sha256
+# returns the serial or fingerprint as ASCII
 #
 determine_cert_fingerprint_serial() {
      local cert="$1"
@@ -8444,6 +8446,10 @@ determine_cert_fingerprint_serial() {
      result="${result//:/}"
      result="${result//SHA1 /}"
      result="${result//SHA256 /}"
+     # When the serial number is too large we'll get a 0x0a LF after 70 ASCII chars (see #2010).
+     # Thus we clean them here so that it is displayed correctly.
+     result="${result/[$'\n\r']/}"
+     result="${result//[\\]/}"
      safe_echo "$result"
 }
 
@@ -8549,6 +8555,7 @@ certificate_info() {
      local -i secsaday=86400
      local first=true
      local badocsp=1
+     local len_cert_serial=0
 
      if [[ $number_of_certificates -gt 1 ]]; then
           [[ $certificate_number -eq 1 ]] && outln
@@ -8885,12 +8892,31 @@ certificate_info() {
 
      hostcert="$(<$HOSTCERT)"
 
-     out "$indent"; pr_bold " Serial / Fingerprints        "
+     out "$indent"; pr_bold " Serial                       "
      cert_serial="$(determine_cert_fingerprint_serial "$hostcert" "-serial")"
      fileout "cert_serialNumber${json_postfix}" "INFO" "$cert_serial"
+     out "$cert_serial"
 
+     len_cert_serial=${#cert_serial}
+     len_cert_serial=$(( len_cert_serial / 2 ))
+
+     if [[ $len_cert_serial -gt 20 ]]; then
+          # https://datatracker.ietf.org/doc/html/rfc5280#section-4.1.2.2
+          outln
+          prln_svrty_low "${spaces}NOT ok: length must not exceed 20 bytes (is: $len_cert_serial bytes)"
+          fileout "cert_serialNumberLen${json_postfix}" "LOW" "$len_cert_serial is too long"
+     elif [[ $len_cert_serial -lt 8 ]]; then
+          # Wording is from https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.8.0.pdf
+          prln_svrty_low "   NOT ok: length should be >= 64 bits entropy (is: $len_cert_serial bytes)"
+          fileout "cert_serialNumberLen${json_postfix}" "LOW" "$len_cert_serial is not enough entropy"
+     else
+          outln " (OK: length $len_cert_serial)"
+          fileout "cert_serialNumberLen${json_postfix}" "INFO" "$len_cert_serial"
+     fi
+
+     out "$indent"; pr_bold " Fingerprints                 "
      cert_fingerprint_sha1="$(determine_cert_fingerprint_serial "$hostcert" "-fingerprint -sha1")"
-     outln "$cert_serial / SHA1 $cert_fingerprint_sha1"
+     outln "SHA1 $cert_fingerprint_sha1"
      fileout "cert_fingerprintSHA1${json_postfix}" "INFO" "${cert_fingerprint_sha1}"
 
      cert_fingerprint_sha2="$(determine_cert_fingerprint_serial "$hostcert" "-fingerprint -sha256")"