tls Forward Secrecy edit
fr15-10-20, forward secrecy
FS 
protects past sessions against future compromises of secret keys or passwords. In Transport Layer Security it depends on Diffie-Hellman key exchange or elliptic curve Diffie-Hellman-based FS.
Code snippet to filter ciphers with tcl_patchLevel 8.6.4 and tls 1.6.7.1
package require tls
# avoid RC4 vulnerability attack
set psf [lsearch -all -inline -not [tls::ciphers tls1] *RC4*]
# only DHE
set psf [lsearch -all -inline $psf *DHE*]
tls::init -request 0 -require 0 -ssl2 0 -ssl3 0 \
-tls1 0 \
-tls1.1 1 \
-tls1.2 1 \
-ciphers $psf \
-certfile certs/server.pem \
-keyfile certs/skey.pem
For evaluation the code above replaces tls::init in tclhttpd(v 3.5.3)'s httpd.tcl. httpd.tcl is located in the bin directory.
In tclhttpd.rc we have
Config https_port 443
- the lines starting with "Config SSL_" will be ignored
- tclhttpd.rc would be a better place to set the psf-ciphers, however a package require tls inside will fail
The key files are located in bin/certs Create a self signed certificate:
openssl genrsa -des3 -out server.key 2048
# with passphrase ... used
#make insecure key
openssl rsa -in server.key -out server.key.insec
mv server.key server.key.sec
mv server.key.insec server.key
#make csr
openssl req -new -key server.key -out server.csr
#self sign
openssl x509 -req -days 1001 -in server.csr -signkey server.key -out server.crt
# set your destination path e.g.
set DEST /tclhttpd/bin
mkdir $DEST/certs
cp server.crt $DEST/certs/server.pem
cp server.key $DEST/certs/skey.pem
Check if we have SF
OpenSSL keeps the connection open if SF is supported. Use one of the filtered ciphers:
openssl s_client -connect 127.0.0.1:443 -cipher DHE-RSA-AES128-GCM-SHA256
Possible Vulnerabilities
A check with testssl.sh -U 127.0.0.1:443 gives
testssl.sh 2.7dev from https://testssl.sh/dev/
...
Testing vulnerabilities
Heartbleed (CVE-2014-0160) not vulnerable (OK) (timed out)
CCS (CVE-2014-0224) not vulnerable (OK)
Secure Renegotiation (CVE-2009-3555) not vulnerable (OK)
Secure Client-Initiated Renegotiation VULNERABLE (NOT ok), DoS threat
CRIME, TLS (CVE-2012-4929) not vulnerable (OK)
BREACH (CVE-2013-3587) no HTTP compression (OK) - only supplied "/" tested
POODLE, SSL (CVE-2014-3566) not vulnerable (OK)
TLS_FALLBACK_SCSV (RFC 7507), experim. Downgrade attack prevention supported (OK)
FREAK (CVE-2015-0204) not vulnerable (OK)
LOGJAM (CVE-2015-4000), experimental not vulnerable (OK), common primes not checked. "testssl.sh -E/-e" spots candidates
BEAST (CVE-2011-3389) no SSL3 or TLS1
RC4 (CVE-2013-2566, CVE-2015-2808) no RC4 ciphers detected (OK)
