zeroc00I / TLS-studies

Work in progress

TLS-studies

Work in progress

Drafts from Practical TLS

• HTTPS -> HTML transferred with HTTP protected by SSL

• But can also protect other data transfer

• SSL VPN

• Secure sockets layer (Netscape 1994)

• Transport Layer security (maintenance handed to IETF in 1999 and renamed protocol to TLS)

How the secure is made

• Confidentiality / Encryption

• Integrity / Hashing

• Authentication / PKI

• Anti-replay: Request transfering 100. A MitM trying to repeat the request.

• Provided with built-in sequence numbers

• Built in to integrity + authentication mechanism

• Non repudiation: Sender cannot later deny sending a message

Key players:

• Client Optionally authenticated (rare)

• Server Always authenticated / Always provide the certificate

• Certificate Authority Provides de Trust Anchor Five organizations secure 98% of the internet IdenTrust -> Lets encrypt (51.9) | Digicert -> Geotrust (19.4) | Sectigo -> Comodo (17.5) | Godaddy (6.9) | Globalsign (2.9)

Tls/SSL version

• SSL 1.0 (1994 - Netscape) Never publicly released. Full of flaws.
• SSL 2.0 (1995 - Netscape) Still full of flaws
• SSL 3.0 (1996 - Netscape. Predominant version of SSL through ~ 2014) Introduced concept of certificate chains Added compression capability -> Vulnerabilities was found Options support for adicionar key exchange RFC published 6101 Poodle attack released october 2014 (SSL 3.0)

SSL 3.0 foundation of TLS version we use today: All TLS version are minor incrementor of SSL 3.0

• TLS 1.0 (1990) - RFC 2246 Few minor changes: HMAC support Major vulnerability: BEAST (Attack on CBC ciphers) Mitigated in modern browsers

• TLS 1.1 (2006) - RFC 4346 Formally deprecated "EXPORT grade" ciphers Protection against CBC attack (i.g, BEAST)

TLS v1.0 and TLS v1.1 deprecated March 2021 Fails most compliance (PCI, NIST)

TLS v1.2 (2008) - RFC 5246

• Improved security of key generation
• Introduced suport for AEAD Ciphers (Authenticated Encryption With Associated Data)

TLS v1.3 (2018) - RFC 8446

• Shorter Handshake (2 messaves vs 5+)
• 0-RTT Resumption
• Forward Secrecy required
• AEAD Ciphers required
• Favors security and simplicity over backwars compability
• Insecure algorithms removed

Criptography

Hashing used to provide integrity, it must satisfy four requirements:

• Infeasible to produce a given digest
• Impossible to extract original message
• Slight changes produce drastic differences
• Resulting digest is fixed width (length)

Collision are a bad thing that occurs when two messages result in identical digests Cannot be avoided. Its a byproduct of "fixed width digests" Can only be made more rare

Examples: https://web.archive.org/web/20131020122204/http://www2.mat.dtu.dk/people/S.Thomsen/wangmd5/samples.html

Common Hashing Algorithms:

• Md5 -> 128 bits
• Sha/Sha1 -> 160 bits
• Sha2 Family

Interceptor can modify the message and re-calculate Hash. Receiver compares their Digest against modified Digest Simply hashing the message isnt enought Both parties establish a mutual Secret Key Message Authentication Code (MAC) = Combining Message + Secret Key when calculating Digest Example: HMAC (Hash Based Message Authentication Code)

Encryption: Simple encryption: Transforms plaintext into cipher text

• Doesnt scale
• Hard to do securely
• Cannot simple use a Standard Algorithm

Key Based encryption:

• Combines indestru vetted algorithm with a Secret Key
• Algorithm is created by experts
• Secret Keys can be randomly generated

Two type of Key Based Encryption Symetric -> Encrypt / Decrypt using same keys Asymmetric -> Encrypt / Decrypt using different keys (Two different keys that are mathematically related) One key will be made Public Other key will be kept Private

Symetric:

• Des
• RC4
• 3DES
• AES

Asymmetric:

• DSA
• RSA
• ECDSA
• ECDH
• Diffie-Hellman