Communications Application Security

1. Communications Application Security Dr. Ron Rymon Efi Arazi School of Computer Science IDC, Herzliya. 2010/11 Pre-requisite: Basic Cryptography, Identity Authentication

2. Overview • E-mail Confidentiality (S/MIME, PGP) • Spam and Phishing • Voice over IP Telephony

3. Secure E-mail Pretty Good Privacy (PGP) Secure MIME

4. E-mail Security Requirements • E-mail is one of most widely used network application • Compatibly available on virtually any platform and OS • Now mobile too • Desired Security Services • Confidentiality • Source and Message Integrity Authentication • Intrusion prevention (Viruses) • Content filtering (Spam, Phishing) • Interruption Prevention (Spam, DoS) • Must be cross-platform • Must support asynchronous communication • SMTP does not provide these services • Some control over access to outgoing servers • Added user authentication (1999) • Recent discussion about adding source domain auth @ destination

5. Source Authentication in SMTP

6. Pretty Good Privacy (PGP) • Created by Philip Zimmerman • Free version: OpenPGP, GPG (GNU Privacy Guard) • Enterprise-grade version widely available • Security Services: • Confidentiality • Key exchange: Diffie-Hellman, or RSA • Encryption: CAST-128, or IDEA, or 3DES • Authentication • Digital signature using SHA-1/MD5, and encrypted using DSS/RSA • Attachments also encrypted using PGP’s file encryption protocol • New approaches to combine with MIME • Other services • Compression: ZIP • Partitioning and reassembly of large messages • Available also for icq and wireless communication

7. PGP Confidentiality • Sender processing • Generates a distinct session key per message • Compresses message • Encrypts session key using receiver’s public key • RSA, or ElGamal/DH for key exchange • Encrypts message using session key • Using conventional cryptography faster than RSA • Appends encrypted key and message, and sends • Receiver processing • Decrypts session key using own private key • Decrypts message • Unzips

8. PGP Message Integrity and Source Authentication • Sender processing • Use SHA-1/MD5 to generate 160-bit hash code for the message • Hash code is signed with sender’s private key • Signed hash code is appended to message and sent • Receiver processing • Decrypts the hash code using the sender’s public key • Generates a new hash code from the message • Compares received and computed hash codes • Note: Signatures can be kept detached from the message, e.g., allowing multiple non-nested signatures on same document, and for record purposes

9. PGP Authentication+Confidentiality • Sender processing • Signature is generated first, and appended to message • (Msg+Sig) compressed and encrypted with session key • Session key is encrypted using receiver’s public key • Compression is applied after the signature • Signature can be kept with original message for later verification • Compression algorithm is independent • Encryption applied to compressed message • has less redundancy than original plaintext – harder cryptanalysis

10. PGP Key Management • Session Keys. PGP employs a keystroke-based technique for generating cryptographically strong session keys • Next Session Key = EPrevKey(keystroke) • Rings. PGP allows users to maintain “rings” with multiple pairs of private-public keys • To be able to decrypt messages encrypted with older keys • To communicate with different users using different keys • Each key is identified (almost uniquely) by its rightmost 64 bits • Each key is also indexed by the User ID • Passphrases. Private keys are kept encrypted, using the hash code of a user-chosen passphrase as key

11. PGP Public-Key Management • Key distribution main concern is impersonation • Options: • Alice can physically deliver the key • Alice can e-mail or dictate key to Bob over the phone; Bob can verify the key with Alice using its hash code “fingerprint” • A trusted “introducer” can sign a certificate that contains Alice’s key • Obtain Alice’s key from a trusted certificate authority (key servers) • PGP associates with each key • a set of introducers, and Bob’s trust in each • a level of legitimacy, computed by PGP from the combined legitimacies of the introducers • a level of trust in each user to legitimize another user • Key owner can revoke it by signing revocation certificate

12. S/MIME • Developed by RSA Data Security • Secure / Multipurpose Internet Mail Extension • Built on top of MIME • S/MIME and OpenPGP considered for IETF standard (RFC 2015) • MIME fixes some of the limitations of SMTP (Simple Mail Transfer Protocol) • Large files • Non-ASCII characters (binaries, special) • MIME header allows specification • multiple types, e.g., application/postscript, video/mpeg • multiple transfer encodings, e.g., 7bit, base64 • MIME Messages can be multi-part and contain multiple different contents

13. S/MIME Services • Confidentiality • Enveloped data • Authentication • Signed data: digital signature is created and is encoded with content in radix-64 • Clear-signed data: only signature is encoded in radix-64 and the rest of the message is clear • Confidentiality and Authentication • Nesting of signature and enveloping in either order • New MIME types (pkcs) added

14. S/MIME Algorithms • Message digesting • SHA-1, MD5 • Encrypt message digest • DSS, RSA-512/1024 • Encrypt session key • DH/ElGamal, RSA • Encrypt message with session key • 3DES, RC2-40

15. S/MIME Key Management • Based on a hybrid of X.509 (CA) and PGP (local) • User must establish herself at a recognized CA • Certificate registration and revocation can be communicated using a special MIME type • S/MIME uses CA to verify UserID-public key match • Users manage copies of certificates/keys locally

16. Summary – Email Security • PGP and S/MIME • Both implemented on top of SMTP, which does not provide security • Both implement confidentiality, message and source authentication • Both implemented as post/pre-processor • Both allow a choice of encryption/authentication algs • S/MIME based on centralized CA; PGP is distributed • PGP/MIME and OpenPGP use MIME too • PEM (Privacy Enhanced Mail) • Earlier protocol that was used for text (7-bit) messages

17. Spam and Phishing

18. Spam • Spam is part impersonation part an interruption of service • Primarily porn and marketing • 60-95% of all US mail is spam (2007) • Less in non-english speaking countries • Some companies send 100’s of millions of messages a day • US CAN-SPAM(Controlling Assault of Non-Solicited Pornography and Marketing Act) • enacted in 2004 to regulate pornographic and marketing emails • requires labeling a message – no standard way to do it • requires opt-out facility – cannot opt out entire domain, or to apply to all spammers • Spam is not a virus, but has some similar features: • Usually distributed via e-mail • Some messages attempt to send “live” indicators (web beacons) • Some try to plant a spyware/cookie • Can be filtered based on signatures Barracuda

19. Phishing: What would YOU do if you received this email?

20. Phishing • Masqueraded attempt to extract information • 43% of adults received phishing emails (2005) – 100% now • 60 Million phishing emails/year; 11M clicked (Gartner, 2006) • Common examples • Emails that show graphics of a bank, or refers to a copycat web site, and ask for the user’s banking credentials • Emails that attempt to blackmail employees, e.g., threating to expose that they were browsing a porn site • 419 Nigerian Connection scamming campaigns • Preying on users that mistype a website name, e.g., googkle.com, and try to install a trojan on their machine • Key logging Trojans • Most attempts are linked to professional criminals • Spear Phishing – attacking a specific crowd • Executives of a credit union received a message asking them to download a TH

21. Few Email Phishing Examples Company: Citizens Bank, Date: 4/25/2005Subject line: "Citizens Bank Instant 5 USD reward survey'"Information request: Getting victim's Citizens Bank debit card information. Company: Ameritrade, Date: 4/22/2005Subject line: "Ameritrade Online Application"Information request: Getting victim's login information (username/password). Company: Barclays, Date: 4/20/2005Subject line: "Barclays Verification Service"Information request: Getting victim's Barclays account information. Company: Bank Of America, Date: 4/19/2005Subject line: "Online Banking Alert (Change of Email Address)"Information request:Getting victim's username/password, ATM card info. Company: eBay, Date: 4/18/2005Subject line: "eBay Verify Accounts"Information request: Getting victim's eBay and Paypal username/password, credit card information, bank account information, etc.

22. Anti-Spam/Phishing • Some use source/content filtering techniques • Sender identity (black/white lists) • Correlating IPs to known email servers (IBM FairUCE) • Key words, e.g., xxx, viagra, “make money fast” • Semantic mapping • Some learn from user feedback • Centralized and/or collaborative tagging • Challenges • False positives • Spammers adapt

23. Anti-Spam/Phishing • Some work at client, others at mail gateway • Client: can adapt; one person’s garbage is another’s gold • Gateway: can save a lot of individual effort • Newer anti-spam methods work at ISP level • Identify spam based on their mass distribution • Spam filtering • Like anti-virus, but bigger scale • Shut down spam/phishing URLs • Post-hoc management (Phishing)

24. Fighting Outgoing Spam • ISPs try to block spammers from obtaining e-mail accounts and service • Prevent robotic enrollment through CAPTCHAs • Limit the number of messages from a single account • Hotmail reported 20% fewer new accounts with such measures • ISPs try to block spammers messages • Filter messages and close rogue accounts • Shutdown outgoing mail relaying • Slowing down outgoing messages is a new approach • MSN/Hotmail/AOL report blocking 2B messages/day

25. VoIP Telephony

26. The VoIP (R)evolution • Voice over IP uses data networks to transmit voice (telephony) • 2005 is the year of VoIP adoption • 23% of the top 500 firms are using or at least trying VoIP • 2%t of all US firms use VoIP (19% in 2007) • Most small/medium companies will move to VoIP in next 5 years • In 2005, 73% of wire line service providers and 31% of wireless operators implemented, or are testing VOIP • 50% of Internet households interested in VoIP to save costs • About 1MM subscribers in each of US, Europe, and Asia • Vonage has 500K users and adds 15K/week (Jan 2005)

27. How VoIP Works • Main protocols: H.323, SIP • VoIP can also work wirelessly through WLAN (802.11) • Big boost with fiber optic to the home • Peer-to-peer VoIP (Skype, Fring, Jaja, Viber) • Desktop-based softphone

28. VoIP Potential Vulnerabilities • Inherits most of the security issues of data networks • Eavesdropping, impersonation, rerouting, denial-of-service, etc.

29. VoIP Potential Vulnerabilities • Security became the greatest inhibitor to VoIP; more than budgets • VoIP Security Alliance launched in Feb 2005, www.voipsa.org • Attacks on infrastructure • Denial of service is number one concern (e.g. 911 emergency call) • SPIT - Spamming of voice mailboxes (and phishing for information) • Breaking into PBXs to make calls • Stealing and spoofing phone numbers and calls • Viruses • Attacks on communication • Eavesdropping • Injection of voice (esp. for transcription) • Hijacking and rerouting calls • VoIP phising (vishing) • Traffic analysis – who is calling, when, how long, etc. • Users are 2x more concerned about attacks on infrastructure • VoIP security shall use same solutions as in data networks • But QoS demands real-time solutions (crypto-engine, tunneling…) • VoIP solutions integrating security solutions (e.g., gateways/firewalls)

30. Next Class Guest Lectures Attendance is required !