Random musings on SSL/TLS configuration

Random musings on
SSL/TLS
by Cyrus Dasadia (@ExtremeUnix)

Reason for configuring SSL
Identity
Confidentiality/Privacy
Integrity

Secure my application
Step 1: Create CSR

Step 1: Create CSR
Step 2: Buy / Self-sign a SSL Certificate

Step 1: Create CSR
Step 3: Configure Apache/Nginx web-server

Step 1: Create CSR
Step 3: Configure Apache/Nginx web-server
Step 4: Security Accomplished!!

You were mostly wrong
Cipher suites ?
OpenSSL on system/application?
Certificate Key?
TLS version supported?

SSL ≠ TLS or is it ?
Netscape created SSL
as a product
SSL v1.0 - ??
SSL v2.0 - 1995
SSL v3.0 - 1996

SSL ≠ TLS or is it ?
Netscape created SSL
as a product
SSL v1.0 - ??
SSL v2.0 - 1995
SSL v3.0 - 1996
TLS came as a
standard.
TLS v1.0 - 1999
TLS v1.1 - 2006
TLS v1.2 - 2008
TLS v1.3 - draft

X.509
Hostname validation certs
Extended validation certs

Protocol Versions
● Disable SSL v2.0
● Avoid SSL v3.0
● Disable TLS compression (removed in TLS
1.3)
● Highest priority to TLS 1.2

Ciphers
Plain text
Key
SupaCipher Encrypted
Text

Ciphers: TLS
Symmetric
Block chaining
Recommended AES128 with GCM (Galois/Counter Mode)

Ciphers: TLS
Avoid these ciphers:
DES
EXP-*
RC4

KeyExchange
RSA: Fast but no forward secrecy.
DHE: Forward secrecy but not fast enough.
ECDHE: Fast and forward secrecy

Lets see them in action
https://www.ssllabs.com/ssltest

Random musings on SSL/TLS configuration

Few takeaways: Keys
● 1024 bits is asking for trouble
● 2048 bits minimal viable
● 4096 good standard
● Switch to ECDSA in future!

Few takeaways: Keys
Generating ECDSA keys:
256 bit key:
openssl ecparam -name prime256v1 -genkey -out my.key
512 bit key:openssl ecparam -name secp521r1 -genkey -out my.key

Few takeaways: Choosing a CA
● At least Supports Certificate Revocation List (CRL)
● Supports Online Certificate Status Protocol (OCSP)
● Accept trustiness of your Country/Corp CA

Few takeaways: Renegotiation
Disable Client Initiated Renegotiation
Apache:
Nginx:

Few takeaways: Performance
● Enable session resumption
● Keep-Alive is your friend
● Cache-Control: public

Few takeaways: Security bits
● Ensure 3rd party CDN’s use SSL
● Do not mix connection types

Few takeaways: Security bits
Enable HSTS (HTTP Strict Transport Security) if possible.
Apache: (mod_headers) Header add Strict-Transport-Security "max-age=
15768000;includeSubDomains"
nginx: (mod_headers) add_header Strict-Transport-Security "max-age=
15768000;includeSubDomains"

Few takeaway: Security bits
Apache :
SSLProtocol ALL -SSLv2
SSLHonorCipherOrder on
SSLCipherSuite
ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH
+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:!aNULL:!MD5:!DSS
courtesy: @hynek

Few takeaway: Security bits
nginx :
ssl_prefer_server_ciphers on;
ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers
ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH
+3DES:RSA+AESGCM:RSA+AES:RSA+3DES:!aNULL:!MD5:!DSS;
courtesy: @hynek

STARTTLS ≠ TLS
Plain text communications viz. IMAP, POP,
SMTP needed support for encrypted
connections

STARTTLS ≠ TLS
Simple solution, use a different port
IMAP uses port 143, SSL/TLS port 993.
POP uses port 110, SSL/TLS port 995.
SMTP uses port 25, SSL/TLS port 465.
and LDAP, XMPP, etc.

STARTTLS ≠ TLS
Simple solution, use a different port
IMAP uses port 143, SSL/TLS port 993.
POP uses port 110, SSL/TLS port 995.
SMTP uses port 25, SSL/TLS port 465.
and LDAP, XMPP, etc.
But having 2 ports is just waste of resources....

STARTTLS ≠ TLS
STARTTLS can simply be called to upgrade a plaintext
connection to TLS.

Summary
Disable SSL v2.0
Use ECDHE wherever possible

Summary
Disable SSL v2.0
Use ECDHE wherever possible
Do not trust default pkgs

Random musings on SSL/TLS configuration

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