SSL/TLS konfiguracija: Zašto nije dovoljno imati HTTPS

Razlika između SSL i TLS

Termin "SSL" se i dalje široko koristi, ali SSL (Secure Sockets Layer) kao protokol je zastareo i nesiguran još od sredine 1990-ih. Ono što koristimo danas je TLS (Transport Layer Security) - aktuelne verzije su TLS 1.2 i TLS 1.3. SSL 2.0, SSL 3.0, TLS 1.0 i TLS 1.1 su povučeni i ne smeju biti podržani.

Problemi sa zastarelim TLS verzijama

Svaka stara verzija nosi poznate napade:

• SSL 3.0: POODLE napad (Padding Oracle On Downgraded Legacy Encryption)
• TLS 1.0: BEAST napad (Browser Exploit Against SSL/TLS)
• TLS 1.1: Nema poznatih kritičnih ranjivosti, ali zastarele kriptografske primitive
• TLS 1.2: Siguran uz pravilnu konfiguraciju cipher suitea
• TLS 1.3: Trenutno najsigurniji, eliminisao zastarele algoritme

Cipher Suites - koje algoritme koristite?

Cipher suite je kombinacija algoritama za razmenu ključeva, autentifikaciju, enkripciju i integritet podataka. Primer:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

• ECDHE - Elliptic Curve Diffie-Hellman Ephemeral (razmena ključeva, Perfect Forward Secrecy)
• RSA - autentifikacija sertifikata
• AES_256_GCM - simetrična enkripcija (256-bitni AES u GCM modu)
• SHA384 - hash za integritet

Koje cipher suites treba onemogućiti

• Bilo šta sa NULL (bez enkripcije)
• Bilo šta sa EXPORT (namerno oslabljeni za izvoz, istorijski)
• RC4 - kriptografski slom
• DES, 3DES - zastareli, SWEET32 napad
• Cipher suites bez ECDHE ili DHE - nema Perfect Forward Secrecy

Perfect Forward Secrecy (PFS)

PFS garantuje da kompromitovanje privatnog ključa servera ne otkrije retroaktivno prošle sesije. Cipher suites sa ECDHE ili DHE pružaju PFS - za svaku sesiju generiše se novi, privremeni ključ koji se posle baca.

HSTS i Certificate Transparency

HSTS (HTTP Strict Transport Security) nalaže browseru da uvek koristi HTTPS za vaš sajt - čak i ako korisnik kuca http://. Certificate Transparency (CT) logovi su javni zapisi svih izdatih sertifikata - proverite da niko nije izdao sertifikat za vaš domen bez vašeg znanja.

Sertifikat - šta proveriti

• Datum isteka (renewal mora biti pre isteka, ne posle!)
• Domen pokrivenost (wildcard *.domen.rs vs. specifični subdomain)
• Issuer - da li je sertifikat izdat od poznate CA?
• Subject Alternative Names (SAN) - da li pokriva sve potrebne domene?
• Revocation status (OCSP) - da li je sertifikat opozvan?

Kako proveriti konfiguraciju

SSL Labs (ssllabs.com/ssltest) je besplatan alat koji daje sveobuhvatnu ocenu (A+ do F) vaše TLS konfiguracije. Shieldome Scout uključuje automatizovanu procenu SSL/TLS kao deo svakog skeniranja: proverava podržane verzije, cipher suites, sertifikatne greške, HSTS header i HTTPS redirect.

The Difference Between SSL and TLS

The term "SSL" is still widely used, but SSL (Secure Sockets Layer) as a protocol has been deprecated and insecure since the mid-1990s. What we use today is TLS (Transport Layer Security) - current versions are TLS 1.2 and TLS 1.3. SSL 2.0, SSL 3.0, TLS 1.0, and TLS 1.1 are deprecated and must not be supported.

Problems with Outdated TLS Versions

Each old version carries known attacks:

• SSL 3.0: POODLE attack (Padding Oracle On Downgraded Legacy Encryption)
• TLS 1.0: BEAST attack (Browser Exploit Against SSL/TLS)
• TLS 1.1: No known critical vulnerabilities, but outdated cryptographic primitives
• TLS 1.2: Secure with proper cipher suite configuration
• TLS 1.3: Currently the most secure, eliminated outdated algorithms

Cipher Suites - What Algorithms Are You Using?

A cipher suite is a combination of algorithms for key exchange, authentication, encryption, and data integrity. Example:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

• ECDHE - Elliptic Curve Diffie-Hellman Ephemeral (key exchange, Perfect Forward Secrecy)
• RSA - certificate authentication
• AES_256_GCM - symmetric encryption (256-bit AES in GCM mode)
• SHA384 - hash for integrity

Perfect Forward Secrecy (PFS)

PFS guarantees that compromising the server's private key does not retroactively reveal past sessions. Cipher suites with ECDHE or DHE provide PFS - for each session, a new, temporary key is generated and then discarded.

Certificate - What to Check

• Expiry date (renewal must happen before expiry, not after!)
• Domain coverage (wildcard *.domain.com vs. specific subdomain)
• Issuer - was the certificate issued by a known CA?
• Subject Alternative Names (SAN) - does it cover all needed domains?
• Revocation status (OCSP) - has the certificate been revoked?

How to Check Your Configuration

SSL Labs (ssllabs.com/ssltest) is a free tool that gives a comprehensive rating (A+ to F) of your TLS configuration. Shieldome Scout includes automated SSL/TLS assessment as part of every scan: it checks supported versions, cipher suites, certificate errors, HSTS header, and HTTPS redirect.