Introduction to Information Security

Transcription

1 Introduction to Information Security , Spring 2015 Lecture 9: Low-level platform attacks, Trusted platform, TCP/IP security (1/2) Eran Tromer 1 Slides credit: Dan Boneh, Stanford Itamar Gilad and Nir Krakowsky and Avishai Wool, Tel Aviv University Steve Weiss, PrivateCore

2 Boot sequence / virtualization BIOS CIH (1998): CIH virus corrupts system BIOS Heasman (2007): System Management Mode (SMM) rootkit via EFI invisible to OS and VMM Sacco, Ortega (2009): infect BIOS LZH decompressor OS loading Master Boot Record / Boot Sector Virtualization: Subvirt, Blue Pill 2

3 Hardware implants Malware in firmware, persists across OS reinstall Hard disks Keyboard controllers PCI/PCIe cards Direct Memory Access (DMA) by PCI/PCIe cards and Firewire/Thunderbolt peripherals Countermeasure: IOMMU (e.g., Intel VT-D) Countermeasure: Software Guard Extensions (SGX) encrypts memory All practical and used (leaked ANT catalog of the National Security Agency) See talk by Steve Weiss at Black Hat

4 SMM attack 4

5 Hard disk firmware attack 5

6 PXIe card attack Intelligent Network Adapter Boots independently of host Exfiltrates data over network 6

7 Physical memory extraction Memory bus analyzer Freeze the state of volatile DRAM and read it on a different machine Cold boot attack (literally freeze) Keep power using capacitor 7

8 DRAM memory bus analyzers 8

9 9 Trusted Platforms via Trusted Computing Architecture

10 Background TCG consortium. Founded in 1999 as TCPA. Main players (promoters): (>200 members) Goals: AMD, HP, IBM, Infineon, Intel, Lenovo, Microsoft, Sun Hardware protected (encrypted) storage: Only authorized software can decrypt data e.g.: protecting key for decrypting file system Secure boot: method to authorize software Attestation: Prove to remote server what software is running on my machine. 10

11 TCG: changes to PC Extra hardware: TPM Trusted Platform Module (TPM) chip Single 33MhZ clock. TPM Chip vendors: (~.3$) Atmel, Infineon, National, STMicro Intel D875GRH motherboard Software changes: BIOS, EFI (UEFI) OS and Apps 11

12 12 TPMs in the real world TPMs widely available on laptops, desktops and some servers Software using TPMs: File/disk encryption: BitLocker, IBM, HP, Softex Attestation for enterprise login: Cognizance, Wave Client-side single sign on: IBM, Utimaco, Wave

13 TPM Basics What the TPM does How to use it 13

14 14 Components on TPM chip LPC bus I/O Non Volatile Storage (> 1280 bytes) PCR Registers ( 16 registers) Other Junk API calls Crypto Engine: RSA, SHA-1, HMAC, RNG RSA: 1024, 2048 bit modulus SHA-1: Outputs 20 byte digest

15 Non-volatile storage 1. Endorsement Key (EK) (2048-bit RSA) Created at manufacturing time. Cannot be changed. Used for attestation (described later) 2. Storage Root Key (SRK) (2048-bit RSA) Used for implementing encrypted storage Created after running TPM_TakeOwnership( OwnerPassword, ) Can be cleared later with TPM_ForceClear from BIOS 3. OwnerPassword (160 bits) and persistent flags 15 Private EK, SRK, and OwnerPwd never leave the TPM

16 PCR: the heart of the matter PCR: Platform Configuration Registers Lots of PCR registers on chip (at least 16) Register contents: 20-byte SHA-1 digest (+junk) Updating PCR #n : TPM_Extend(n,D): PCR[n] SHA-1 ( PCR[n] D ) TPM_PcrRead(n): returns value(pcr(n)) 16 PCRs initialized to default value (e.g. 0) at boot time TPM can be told to restore PCR values in NVRAM via TPM_SaveState and TPM_Startup(ST_STATE) for system suspend/resume

17 Using PCRs during the boot process BIOS boot block executes Calls TPM_Startup (ST_CLEAR) to initialize PCRs to 0 Calls PCR_Extend( n, <BIOS code> ) Then loads and runs BIOS post boot code BIOS executes: Calls PCR_Extend( n, <MBR code> ) Then runs MBR (master boot record), e.g. GRUB. 17 MBR executes: Calls PCR_Extend( n, <OS loader code, config> ) Then runs OS loader and so on

18 Boot process with TPM Hardware BIOS boot block BIOS MBR OS loader OS Application Root of trust in integrity measurement TPM Root of trust in integrity reporting measuring Extend PCR After boot, PCRs contain hash chain of booted software Reliable summary of the current platform, assuming: 18 Every step correctly measures the next one (and in particular has no vulnerabilities that circumvent measurement) The BIOS boot block is not compromised The PCR initialized to 0 and is modified only by extending it Collision resistance of SHA-1

19 19 Example: Trusted GRUB (IBM 05) What PCR # to use and what to measure specified in GRUB config file

20 Using PCR values after boot Application 1: encrypted (a.k.a sealed) storage. Step 1: TPM_TakeOwnership( OwnerPassword, ) Creates 2048-bit RSA Storage Root Key (SRK) on TPM Cannot run TPM_TakeOwnership again without OwnerPwd: Ownership Enabled Flag False Done once by IT department or laptop owner. (optional) Step 2: TPM_CreateWrapKey / TPM_LoadKey Create more RSA keys on TPM protected by SRK Each key identified by 32-bit keyhandle 20

21 Protected Storage Main Step: Encrypt data using RSA key on TPM TPM_Seal (some) Arguments: keyhandle: which TPM key to encrypt with KeyAuth: Password for using key `keyhandle PcrValues: PCRs to embed in encrypted blob data block: at most 256 bytes (2048 bits) Used to encrypt symmetric key (e.g. AES) Returns encrypted blob. 21 Main point: blob can only be decrypted with TPM_Unseal when PCR-reg-vals = PCR-vals in blob. TPM_Unseal will fail othrewise

22 Protected Storage Embedding PCR values in blob ensures that only certain apps can decrypt data. e.g.: Messing with MBR or OS kernel will change PCR values. 22

23 Sealed storage: applications Lock software on machine: OS and apps sealed with MBR s PCR. Any changes to MBR (to load other OS) will prevent locked software from loading. Prevents tampering and reverse engineering Web server: seal server s SSL private key Goal: only unmodified Apache can access SSL key Problem: updates to Apache or Apache config General problem with software upgrades/patches: Upgrade process must re-seal all blobs with new PCRs 23

24 Security? Resetting TPM after boot Attacker can disable TPM until after boot, then extend PCRs arbitrarily (one-byte change to boot block) [Kauer 07] Software attack: send TPM_Init on LPC bus allows calling TPM_Startup again (to reset PCRs) Simple hardware attack: use a wire to connect TPM reset pin to ground Once PCRs are reset, they can be extended to reflect a fake configuration. Rollback attack on encrypted blobs undo security patches 24

25 Better root of trust Late launch: securely load OS/VMM, even on a potentially-compromised machine DRTM Dynamic Root of Trust Measurement New CPU instruction: Intel TXT: SENTER Atomically does: AMD: SKINIT Reset CPU. Reset PCR 17 to 0. Load given Secure Loader (SL) code into I-cache Extend PCR 17 with SL Jump to SL BIOS boot loader is no longer root of trust Avoids TPM_Init attack: TPM_Init sets PCR 17 to 25

26 Protecting code on an untrusted platform 26 Can we run sensitive code on a potentiallycompromised platform, without rebooting/replacing it? Many ways to read and corrupt code! Secure enclave using hardware Possible with SENTER/SKINIT but cumbersome (Flicker project) Intel Software Guard Extensions (SGX) ARM TrustZone Cryptography Fully-homomorphic encryption encryption Succinct zero-knowledge proofs (SNARKs) and Proof-Carrying Data

27 Attestation 27

28 28 Attestation: what it does Goal: prove to remote party what software is running on my machine. Good applications: Bank allows money transfer only if customer s machine runs up-to-date OS patches. Enterprise allows laptop to connect to its network only if laptop runs authorized software Quake players can join a Quake network only if their Quake client is unmodified. DRM: MusicStore sells content for authorized players only.

29 30 Attestation: how it works Step 2: sign PCR values (after boot) Call TPM_Quote (some) Arguments: keyhandle: which AIK key to sign with KeyAuth: Password for using key `keyhandle PCR List: Which PCRs to sign. Data Challenge string from remote server (prevents replay of old signatures) Additional user data to sign Returns signed data and signature.

30 32 TCP/IP security

31 Internet Infrastructure ISP Backbone ISP Local and interdomain routing TCP/IP for routing and messaging BGP for routing announcements DNS (Domain Name System DNS) Find IP address from domain name 33

32 TCP/IP Packets Application message TCP Header Application message - data Transport (TCP, UDP) segment TCP data TCP data TCP data Network (IP) packet IP TCP data Link Layer frame ETH IP TCP data ETF IP Header Link (Ethernet) Header Link (Ethernet) Trailer 34

33 Inside a LAN: Layer 2 issues - ARP 35 35

34 Addressing in Layer 2 / Layer 3 Layer 3 (IP) IP Address 32 bits long Layer 2 (MAC) MAC address 48 bits long How to translate from IP address to MAC address? Layer 2.5 protocol : ARP 36

35 ARP (Address Resolution Protocol) ARP request broadcast to all stations on LAN Computer A asks the network, "Who has this IP address? 37

36 ARP(2) ARP reply Computer B tells Computer A, "I have that IP. My Physical Address is [whatever it is]. 38

37 Cache Table Every computer stores the translations it knows in a cache To view: arp a 39

38 ARP Poisoning To avoid making an ARP request before sending every IP packet, each host has a local cache. Another trick to avoid excessive ARP requests, is that every host will send a broadcast ARP reply when it comes online / every interval, to let everyone know its MAC address (known as Gratuitous ARP ) Most implementations are state-less by design, and will happily store ARP replies even if they didn t issue a request (for reasons stated above) Result everyone on the local network can impersonate any other host, by sending a malicious ARP reply in their name.

39 ARP Poisoning Simplicity also leads to insecurity No Authentication ARP provides no way to verify that the responding device is really who it says it is Stateless protocol Attacks Denial of Service (DoS) Hacker can easily associate an operationally significant IP address to a false MAC address Man-in-the-Middle Intercept network traffic between two devices in your network 41

40 42 Man-In-The-Middle: poison #1

41 43 Man-In-The-Middle: poison #2

42 44 Man-In-The-Middle: success!

43 Promiscuous mode Normally, the network card will listen to every incoming packet, and discard any packet whose destination MAC address is not its own. When someone is running a sniffer, they ll want to capture as much information as possible about the network. Network cards can support this by going into what s called Promiscuous mode where every packet received is sent to the OS for further processing.

44 Detecting Promiscuous Hosts We want to detect if someone on our network is using a sniffer in promiscuous mode. The trick Send out a ping request with the wrong destination MAC address, but the right IP target (or broadcast). Regular hosts will discard the packet, but anyone in promiscuous mode will reply, since the IP target was valid

45 Layer 3 issues - IP 47

46 IP Internet Protocol Connectionless Unreliable Best effort Version Flags Header Length Type of Service Total Length Identification Fragment Offset Notes: src and dest ports not parts of IP header Time to Live Protocol Header Checksum Source Address of Originating Host Destination Address of Target Host Options Padding IP Data 48

47 IP Routing Meg Source Destination Packet Office gateway Tom ISP Typical route uses several hops IP: no ordering or delivery guarantees 49

48 IP Protocol Functions (Summary) Routing IP host knows location of router (gateway) IP gateway must know route to other networks Fragmentation and reassembly If max-packet-size less than the user-data-size Error reporting ICMP packet to source if packet is dropped TTL field: decremented after every hop Packet dropped if TTL=0. Prevents infinite loops. 50

49 51 Basic IP tools

50 IP spoofing : no src IP authentication Client is trusted to embed correct source IP Easy to override using raw sockets SCAPY, libnet: tools for formatting raw packets with arbitrary IP headers Anyone who owns their machine can send packets with arbitrary source IP response will be sent back to forged source IP Implications: Anonymous DoS attacks Anonymous infection attacks (e.g. slammer worm) 52

51 Routing Vulnerabilities 53 53

52 Interdomain Routing earthlink.net Stanford.edu BGP Autonomous System (AS) OSPF connected group of one or more Internet Protocol prefixes under a single routing policy (aka domain) 54

53 Routing Vulnerabilities Routing protocols: OSPF: used for routing within an AS BGP: routing between ASs Attacker can cause entire Internet to send traffic for a victim IP to attacker s address. Some examples: 2008: YouTube IP address space redirected to Pakistan (censorship done wrong ) 2010: Chinese IP publishes 37,000 prefixes covering many many major websites 55

54 56 Whois: IP/Domain/AS information

55 BGP example [D. Wetherall]

56 BGP Security Issues BGP path attestations are un-authenticated Attacker can inject advertisements for arbitrary routes Advertisement will propagate everywhere Used for DoS, spam, and eavesdropping Human error problems: Mistakes quickly propagate to the entire Internet Not quite as bad it as it could be because BGP operators are a closed club with selective acceptance and some internal sanctions. 58