Check for RFC 8879 certificate compression

This commit adds a check for whether the server supports certificate compression (RFC 8879). If it does, then the list of supprted compression methods is output in the server's preference order.

CHANGELOG.md

@@ -30,6 +30,7 @@
 * Headerflag X-XSS-Protection is now labeled as INFO
 * Client simulation runs in wide mode which is even better readable
 * Added --reqheader to support custom headers in HTTP requests
+* Test for support for RFC 8879 certificate compression
 
 
 ### Features implemented / improvements in 3.0

CREDITS.md

@@ -23,12 +23,13 @@ Full contribution, see git log.
   - experimental "eTLS" detection
   - parallel mass testing!
   - RFC <--> OpenSSL cipher name space switches for the command line
-  - better error msg suppression (not fully installed openssl
+  - better error msg suppression (not fully installed openssl)
   - GREASE support
   - Bleichenbacher / ROBOT vulnerability test
   - several protocol preferences improvements
   - pwnedkeys.com support
   - CT support
+  - RFC 8879, certificate compression
   - Lots of fixes and improvements
 
 ##### Further credits (in alphabetical order)

testssl.sh

@@ -7510,6 +7510,49 @@ determine_tls_extensions() {
      return $success
 }
 
+# Return a list of the certificate compression methods supported (RFC 8879)
+determine_cert_compression() {
+     #                                          1=zlib, 2=brotli, 3=zstd
+     local -a supported_compression_methods=("" "false" "false" "false")
+     local -i i len nr_compression_methods=3
+     local len1 len2 methods_to_test method_found method_nr methods_found=""
+
+     # Certificate compression is only supported by TLS 1.3.
+     [[ $(has_server_protocol "tls1_3") -eq 1 ]] && tm_out "" && return 1
+     while true; do
+          methods_to_test=""
+          for (( i=1; i <= nr_compression_methods; i++ )); do
+               ! "${supported_compression_methods[i]}" && methods_to_test+=" ,00,$(printf "%02x" $i)"
+          done
+          len=$((2*${#methods_to_test}/7))
+          # If there are no more compression methods remaining to be tested, then quit.
+          [[ $len -eq 0 ]] && break
+          len1=$(printf "%02x" "$len")
+          len2=$(printf "%02x" "$((len+1))")
+          tls_sockets "04" "$TLS13_CIPHER" "all+" "00,1b, 00,$len2, $len1$methods_to_test"
+          if [[ $? -ne 0 ]]; then
+               add_proto_offered tls1_3 no
+               tm_out ""
+               return 1
+          fi
+          add_proto_offered tls1_3 yes
+          method_found="$(awk '/Certificate Compression Algorithm: / { print $4 $5 }' "$TEMPDIR/$NODEIP.parse_tls_serverhello.txt")"
+          [[ -z "$method_found" ]] && break
+          [[ -z "$methods_found" ]] && tmpfile_handle ${FUNCNAME[0]}.txt "$TEMPDIR/$NODEIP.parse_tls_serverhello.txt"
+          method_found="${method_found//(//}"
+          method_found="${method_found//)/}"
+          method_nr="${method_found%%/*}"
+          supported_compression_methods[method_nr]=true
+          methods_found+=" $method_found"
+     done
+     if [[ -n "$methods_found" ]]; then
+          methods_found="${methods_found:1}"
+     else
+          methods_found="none"
+     fi
+     tm_out "$methods_found"
+     return 0
+}
 
 extract_certificates() {
      local version="$1"
@@ -9500,6 +9543,7 @@ run_server_defaults() {
      local -a ciphers_to_test certificate_type
      local -a -i success
      local cn_nosni cn_sni sans_nosni sans_sni san tls_extensions client_auth_ca
+     local cert_compression_methods
      local using_sockets=true
 
      "$SSL_NATIVE" && using_sockets=false
@@ -9707,6 +9751,9 @@ run_server_defaults() {
      done
 
      determine_tls_extensions
+     cert_compression_methods="$(determine_cert_compression)"
+     [[ -n "$cert_compression_methods" ]] && [[ "$cert_compression_methods" != "none" ]] && \
+          extract_new_tls_extensions "$TEMPDIR/$NODEIP.determine_cert_compression.txt"
 
      if [[ $? -eq 0 ]] && [[ "$OPTIMAL_PROTO" != -ssl2 ]]; then
           cp "$TEMPDIR/$NODEIP.determine_tls_extensions.txt" $TMPFILE
@@ -9847,6 +9894,16 @@ run_server_defaults() {
 
      tls_time
 
+     jsonID="cert_compression"
+     if [[ $(has_server_protocol "tls1_3") -eq 0 ]]; then
+          jsonID="certificate_compression"
+          pr_bold " Certificate Compression      "
+          outln "$cert_compression_methods"
+          fileout "$jsonID" "INFO" "$cert_compression_methods"
+     else
+         fileout "$jsonID" "INFO" "N/A"
+     fi
+
      jsonID="clientAuth"
      pr_bold " Client Authentication        "
      outln "$CLIENT_AUTH"
@@ -13137,6 +13194,7 @@ parse_tls_serverhello() {
      local tls_msg_type tls_content_type tls_protocol tls_protocol2 tls_hello_time
      local tls_err_level tls_err_descr_no tls_cipher_suite rfc_cipher_suite tls_compression_method
      local tls_extensions="" extension_type named_curve_str="" named_curve_oid
+     local cert_compression_method="" cert_compression_method_str=""
      local -i i j extension_len extn_len tls_extensions_len ocsp_response_len=0 ocsp_response_list_len ocsp_resp_offset
      local -i certificate_list_len certificate_len cipherlist_len
      local -i curve_type named_curve
@@ -13401,18 +13459,20 @@ parse_tls_serverhello() {
                     [[ $DEBUG -ge 1 ]] && tmpfile_handle ${FUNCNAME[0]}.txt
                     return 1
                fi
+               cert_compression_method="${tls_handshake_ascii:i:4}"
+               case $cert_compression_method in
+                    0001) cert_compression_method_str="ZLIB" ;;
+                    0002) cert_compression_method_str="Brotli" ;;
+                    0003) cert_compression_method_str="Zstandard" ;;
+                    *)    cert_compression_method_str="unrecognized" ;;
+               esac
                if [[ $DEBUG -ge 3 ]]; then
-                    tm_out "          Certificate Compression Algorithm: ${tls_handshake_ascii:i:4}"
-                    case ${tls_handshake_ascii:i:4} in
-                         0001) tmln_out " (ZLIB)" ;;
-                         0002) tmln_out " (Brotli)" ;;
-                         0003) tmln_out " (Zstandard)" ;;
-                         *)    tmln_out ;;
-                    esac
+                    tmln_out "          Certificate Compression Algorithm: $cert_compression_method ($cert_compression_method_str)"
                     offset=$((i+4))
                     tmln_out "          Uncompressed certificate length:   $(printf "%d" 0x${tls_handshake_ascii:offset:6})"
                     tmln_out
                fi
+               tls_extensions+="TLS server extension \"compress_certificate\" (id=27), len=0\n"
                if [[ "$process_full" =~ all ]] && "$HAS_ZLIB" && [[ "${tls_handshake_ascii:i:4}" == 0001 ]]; then
                     offset=$((i+4))
                     tls_certificate_ascii_len=2*0x${tls_handshake_ascii:offset:6}
@@ -13872,6 +13932,9 @@ parse_tls_serverhello() {
           esac
           echo "===============================================================================" >> $TMPFILE
      fi
+     if [[ -n "$cert_compression_method" ]]; then
+          echo "Certificate Compression Algorithm: $cert_compression_method ($cert_compression_method_str)" >> $TMPFILE
+     fi
      [[ -n "$tls_extensions" ]] && echo -e "$tls_extensions" >> $TMPFILE
 
      if [[ $DEBUG -ge 3 ]]; then
@@ -14827,6 +14890,23 @@ prepare_tls_clienthello() {
                all_extensions+="$extension_supported_point_formats"
           fi
 
+          if [[ "0x$tls_low_byte" -ge 0x04 ]] && [[ ! "$extra_extensions_list" =~ " 001b " ]]; then
+               # If the response needs to be decrypted, then indicate support
+               # for ZLIB certificate compression if $OPENSSL can decompress
+               # the result. If the response does not need to be decrypted,
+               # then indicate support for all certificate compression methods,
+               # as the response does not need to be decompressed.
+               if [[ "$process_full" =~ all ]]; then
+                    if "$HAS_ZLIB"; then
+                         [[ -n "$all_extensions" ]] && all_extensions+=","
+                         all_extensions+="00,1b,00,03,02,00,01"
+                    fi
+               else
+                    [[ -n "$all_extensions" ]] && all_extensions+=","
+                    all_extensions+="00,1b,00,07,06,00,01,00,02,00,03"
+               fi
+          fi
+
           if [[ -n "$extra_extensions" ]]; then
                [[ -n "$all_extensions" ]] && all_extensions+=","
                all_extensions+="$extra_extensions"