NETWORK
SECURITY SSL/TLS.

SSL vs TLS

TLS Versions Comparison

Version	Year	Ciphers	Security	Status
TLS 1.0	1999	CBC, RC4, 3DES	Weak (BEAST, POODLE)	Deprecated
TLS 1.1	2006	CBC, 3DES	Weak (padding oracle)	Deprecated
TLS 1.2	2008	GCM, CCM, CBC	Secure (with strong ciphers)	Recommended
TLS 1.3	2018	GCM, ChaCha20, Poly1305	Very Secure	Recommended (modern)

TLS Handshake

TLS 1.2 Handshake (4 steps)

Client                                    Server
  |                                          |
  |--- ClientHello (ciphers, TLS version) -->|
  |                                          |
  |<- ServerHello (cipher, cert, key, etc) --|
  |                                          |
  |--- ClientKeyExchange (pre‑master secret)-|
  |--- ChangeCipherSpec -------------------->|
  |--- Finished ---------------------------->|
  |                                          |
  |<- ChangeCipherSpec ----------------------|
  |<- Finished ------------------------------|
  |                                          |
  |  Secure tunnel established               |

TLS 1.3 Handshake (faster, 1‑RTT)

Client                                       Server
  |                                             |
  |--- ClientHello (key share, ciphers) ------->|
  |                                             |
  |<- ServerHello (key share, cert) ------------|
  |<- Finished ---------------------------------|
  |                                             |
  |--- Finished --------------------------------|
  |                                             |
  |  Secure tunnel established (0‑RTT optional) |

Key Exchange Methods

• RSA – classic, used in TLS 1.2
• Diffie‑Hellman (DHE) – ephemeral, perfect forward secrecy
• Elliptic Curve Diffie‑Hellman (ECDHE) – efficient, PFS, recommended
• PSK – Pre‑Shared Key (IoT, embedded)
• TLS 1.3 – requires DHE or ECDHE (no static RSA)

Certificates (x.509)

Certificate Chain

Root CA (trusted)
    │
    ├── Intermediate CA 1
    │       │
    │       ├── Intermediate CA 2
    │       │       │
    │       │       └── Server Certificate (your domain)
    │       │
    │       └── Server Certificate
    │
    └── Intermediate CA 3
            │
            └── Server Certificate

OpenSSL Commands

# Generate private key (RSA 2048)
openssl genrsa -out private.key 2048

# Generate CSR (Certificate Signing Request)
openssl req -new -key private.key -out request.csr

# Self‑signed certificate (dev testing)
openssl req -x509 -new -nodes -key private.key -sha256 -days 365 -out certificate.crt

# View certificate
openssl x509 -in certificate.crt -text -noout

# Verify certificate chain
openssl verify -CAfile ca.crt certificate.crt

# Convert PEM to PKCS12 (for Windows/Java)
openssl pkcs12 -export -out certificate.pfx -inkey private.key -in certificate.crt -certfile ca.crt

# Check SSL/TLS configuration of a server
openssl s_client -connect example.com:443 -tls1_2

# Check with SNI
openssl s_client -servername example.com -connect example.com:443

Nginx SSL Configuration (Modern)

server {
    listen 443 ssl http2;
    server_name example.com;

    ssl_certificate     /etc/ssl/certs/fullchain.pem;
    ssl_certificate_key /etc/ssl/private/private.key;

    # TLS versions (no SSL or TLS 1.0/1.1)
    ssl_protocols TLSv1.2 TLSv1.3;

    # Strong ciphers (TLS 1.2)
    ssl_ciphers 'ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305';

    # Prefer server ciphers
    ssl_prefer_server_ciphers off;

    # DH parameter (2048+ bits)
    ssl_dhparam /etc/ssl/certs/dhparam.pem;

    # HSTS (HTTP Strict Transport Security)
    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

    # OCSP stapling
    ssl_stapling on;
    ssl_stapling_verify on;
}

Apache SSL Configuration (Modern)

SSLEngine on
SSLCertificateFile /etc/ssl/certs/fullchain.pem
SSLCertificateKeyFile /etc/ssl/private/private.key

# TLS versions
SSLProtocol all -SSLv3 -TLSv1 -TLSv1.1

# Strong ciphers
SSLCipherSuite ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305
SSLHonorCipherOrder off

# HSTS
Header always set Strict-Transport-Security "max-age=31536000; includeSubDomains"

Cipher Suites (TLS 1.2)

Cipher Suite	Key Exchange	Authentication	Encryption	Hash	Security
ECDHE-ECDSA-AES128-GCM-SHA256	ECDHE	ECDSA	AES128-GCM	SHA256	Very Strong
ECDHE-RSA-AES128-GCM-SHA256	ECDHE	RSA	AES128-GCM	SHA256	Very Strong
ECDHE-ECDSA-CHACHA20-POLY1305	ECDHE	ECDSA	ChaCha20-Poly1305	SHA256	Very Strong
ECDHE-RSA-AES256-GCM-SHA384	ECDHE	RSA	AES256-GCM	SHA384	Very Strong
DHE-RSA-AES128-GCM-SHA256	DHE	RSA	AES128-GCM	SHA256	Strong
RSA-AES128-GCM-SHA256	RSA	RSA	AES128-GCM	SHA256	Weak (no PFS)
RSA-AES128-CBC-SHA	RSA	RSA	AES128-CBC	SHA	Weak (deprecated)

TLS 1.3 Cipher Suites

• TLS_AES_128_GCM_SHA256 – AES 128 GCM
• TLS_AES_256_GCM_SHA384 – AES 256 GCM
• TLS_CHACHA20_POLY1305_SHA256 – ChaCha20
• TLS_AES_128_CCM_SHA256 – AES 128 CCM

Common Attacks & Mitigations

Attack	Description	Mitigation
POODLE	SSLv3 CBC padding oracle	Disable SSLv3, use TLS 1.2+
BEAST	TLS 1.0 CBC attack	Use TLS 1.2+, GCM ciphers
Heartbleed	OpenSSL heartbeat read overflow	Upgrade OpenSSL, revoke keys/certs
FREAK	Export‑grade cipher downgrade	Disable export ciphers
Logjam	DHE export‑grade downgrade	Use ECDHE, disable DHE_EXPORT
Sweet32	64‑bit block cipher (3DES)	Disable 3DES, use AES
DROWN	Cross‑protocol SSLv2 attack	Disable SSLv2, SSLv3
Perfect Forward Secrecy (PFS)	Not an attack – lack of PFS	Use ECDHE or DHE

Best Practices

• Use TLS 1.2 or TLS 1.3 – disable SSL and TLS 1.0/1.1
• Use strong ciphers – GCM/ChaCha20, avoid CBC (unless TLS 1.3)
• Enable Perfect Forward Secrecy – use ECDHE or DHE key exchange
• Use 2048‑bit RSA or ECDSA (P‑256, P‑384) – for certificates
• Enable HSTS – Strict‑Transport‑Security header
• Enable OCSP Stapling – improve certificate revocation checking
• Use strong DH parameters – 2048+ bits (or disable static DH)
• Monitor and rotate certificates – before expiration
• Use Let's Encrypt – free, automated certificates
• Test your configuration – with SSL Labs, testssl.sh
• Use Certificate Transparency – for domain validation

Testing Tools

• SSL Labs – https://www.ssllabs.com/ssltest/
• testssl.sh – CLI tool: ./testssl.sh example.com
• openssl s_client – manual testing
• nmap ssl‑enum – discover supported ciphers
• sslyze – Python SSL/TLS scanner

Test with testssl.sh

git clone https://github.com/drwetter/testssl.sh
cd testssl.sh
./testssl.sh https://example.com

# Check specific protocol
./testssl.sh --tls1_3 example.com

Certificates in Code (Java KeyStore)

# Generate Keystore with self‑signed cert
keytool -genkey -alias mydomain -keyalg RSA -keysize 2048 -keystore keystore.jks -validity 365

# List Keystore contents
keytool -list -v -keystore keystore.jks

# Import certificate into truststore
keytool -import -trustcacerts -alias mydomain -file certificate.crt -keystore truststore.jks