Transport Layer Security, Slides of Computer Systems Networking and Telecommunications

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Internet Security 1 (IntSi1)

Prof. Dr. Andreas Steffen

Institute for Internet Technologies and Applications (ITA)

8 Transport Layer

Security (TLS)

TLS Session Example

Secure Network Protocols for the OSI Stack

Application layer ssh, S/MIME, PGP, Kerberos,

WSS

Transport layer TLS, [SSL]

Network layer IPsec

Data Link layer [PPTP, L2TP], IEEE 802.1X,

IEEE 802.1AE, IEEE 802.11i

(WPA2)

Physical layer Quantum Cryptography

Communication

layers

Security protocols

TLS/SSL Protocol Layers

Secure

Transport

Layer

TLS

TLS

TCP

TCP

IP

IP

Application

Application

Transport

Transport

Fragmentation

Fragmentation

Compression

Compression

Authentication

Authentication

Encryption

Encryption

Insecure

Transport

Layer

TCP

TCP

IP

IP

Application

Application

Application

Application

Socket

s

[Compressed] Data

[Compressed] Data MAC

MAC

Padding

Padding

TCP Header

TCP Header

Record Header

Record Header

n * Block Cipher Size

Record Body

Record Body

TLS Record Structure

Application Data (Segment 1)

Application Data (Segment 1)

Record Header

Record Header

Encrypted Data

Encrypted Data

Application Data (Segment 2)

Application Data (Segment 2)

5 Bytes

TLS Handshake Protocol

Server

Server Hello

Server Hello

R

S

R

S

ServerHelloDone

ServerHelloDone

Client

Client Hello

Client Hello

R

C

R

C

Application Data°

Application Data°

Application Data°

Application Data°

Certificate*

ClientKeyExchange

CertificateVerify*

*optional

ServerKeyExchange*

Certificate*

CertificateRequest*

*optional

Finished°

Finished°

ChangeCipherSpec

Finished°

Finished°

ChangeCipherSpec

°encrypted

Implemented SSL/TLS Protocol Versions

• (^) SSL – Secure Sockets Layer Version 2.

Initially developed by Netscape

SSL 2.0 is sensitive to man-in-the-middle attacks leading

e.g. to the negotiation of weak encryption keys

SSL 2.0 should not be used anymore

SSL – Secure Sockets Layer Version 3.

Internet Draft authored by Netscape, November 1996

Supported by all browsers

Vulnerable to the BEAST Cipher-Block-Chaining (CBC) attack

• (^) TLS – Transport Layer Security Version 1.0 (SSL 3.1)

IETF RFC 2246, January 1999

TLS 1.0 ist not backwards compatible to SSL 3.0 (differences

in

MAC computation, PRF function for master_secret and key

material)

Supported by all browsers

Vulnerable to the BEAST Cipher-Block-Chaining (CBC) attack

BEAST – Browser Exploit Against SSL/TLS

• (^) Authors

Thai Duong and Juliano Rizzo presented their exploit on

September 23 2011 at the 7th ekoparty Security Conference

in Buenos Aires.

Exploit

The exploit uses a known-plaintext attack on the Cipher-Block-

Chaining (CBC) encryption vulnerability of SSL 3.0 and TLS 1.

which has been known since 2001 and was fixed by TLS 1.1 in

Approach

The BEAST JavaScript code running in a browser decrypts

encrypted cookies sent via HTTPS within a couple of seconds.

Fix

Temporary workaround: Set up HTTPS web servers with

stream ciphers (e.g. the rather outdated RC4 algorithm)

Migration of HTTPS web servers and browsers to TLS 1.1 or

SSL/TLS Configuration Options

Mozilla Firefox

SSL/TLS Configuration Options

Mozilla Firefox

TLS Enhanced TCP-based Application

Protocols

Service Name Port Secured Service

• (^) https 443/tcp http protocol over TLS
• (^) smtps 465/tcp smtp protocol over TLS

smtp 25/tcp STARTTLS keyword (RFC 2487)

• (^) imaps 993/tcp imap4 protocol over TLS

imap4 143/tcp STARTTLS keyword (RFC 2595)

• (^) pop3s 995/tcp pop3 protocol over TLS

pop3 110/tcp STLS keyword (RFC 2595)

• (^) ldaps 636/tcp ldap protocol over TLS
• (^) ircs 994/tcp irc protocol over TLS
• (^) nntps 563/tcp nntp protocol over TLS