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TPM, UEFI, Trusted Boot, Secure Boot

TPM, UEFI, Trusted Boot, Secure Boot. How Does a PC Boot?. First: History http://en.wikipedia.org/wiki/Booting Code entered on Hand Switches Non-Volatile Memory; infrequent cold boot Development of ROM-based IPL PC developed multi-stage boot process. Power Up Sequence.

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TPM, UEFI, Trusted Boot, Secure Boot

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  1. TPM, UEFI, Trusted Boot, Secure Boot

  2. How Does a PC Boot? • First: History • http://en.wikipedia.org/wiki/Booting • Code entered on Hand Switches • Non-Volatile Memory; infrequent cold boot • Development of ROM-based IPL • PC developed multi-stage boot process

  3. Power Up Sequence • POST – Power On Self Test • http://en.wikipedia.org/wiki/Power-on_self-test • First code that runs • Part of the BIOS • Checks hardware to prevent boot failure • Runs BIOS/POST code in other devices • BIOS must know how to operate devices • Each BIOS crafted for each motherboard

  4. Initial Program Load - IPL • Original PC booted each device in fixed order • Floppy, CD, HDD, Net • Newer BIOS now can change boot order • Loads boot code from device • Secondary boot loader • Stored in particular track of FDD/HDD • Independent of software architecture

  5. Boot Loader • Knows about device architecture • HDD – Partition tables, block size, • File Structure: FAT16, FAT32, NTFS etc • Finds the OS boot program • MS Boot loader • From a particular named file • Linux loader

  6. OS Loader • What you see when the Operating System Starts • Launches and configures the OS for the hardware • Installs relevant device drivers • Checks license and file system • Gets network operating etc

  7. Security • BIOS is in Flash – can be changed • User code can write to flash memory • Attacker can control machine from 1st power • HDD Boot sector can be changed • (boot sector virus) • OS Loader can be changed

  8. TPM and BIOS • BIOS is in control from POST • BIOS asks TPM for verification • BIOS can still be attacked • OS/CPU must protect BIOS • BIOS chip could still be changed • BIOS asks TPM to verify Boot Loader • BIOS could still boot something if verify failed • Hardware still usable if BIOS permits

  9. Secure Boot • BIOS will only boot authenticated boot loader • Boot loader only boots authentic OS • BitLocker must be enabled to secure disk • BIOS cannot then override TPM signing • BIOS could still boot another device unless locked • BIOS could be replaced to use another disc • Original disc still cryptographically secured

  10. TPM Weakness • Should be tamperproof • Used in Games Console • Gamers motivated to break-in • Hardware attack details publish • Split chip open and collect key from Bus • Use brute force decryption for game keys • Manufacture problem not design problem?

  11. UEFI • Duplication between BIOS and OS • Both need device drivers • BIOS – TPM secure boot is optional • UEFI addresses this • UEFI is part of BIOS • Performs Boot Loader function • Checks OS signature without TPM • Will refuse to boot • Knows file structure • Drivers come from OS disk

  12. Features • Larger disks / Newer Hardware • Eliminates boot virus attacks • Secures OS • Gives manufactures' control of hardware use • Can still work with BitLocker/TPM • Still vulnerable • Contains buffer overflow error (Samsung) • BIOS reflashable/rechipable

  13. Unified Extensible Firmware Interface

  14. Fully Trustworthy? • Anti-Evil Maid method • Store signatures of BIOS etc in TPM • User checks TPM signature using: • Password • Physical device (USB stick with crypto key) • All signatures checked • Detects any non-authentic code • BitLocker not needed • Detects compromise on any component

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