KISS:  “Key  it  Simple  and  Secure”   Corporate  Key  Management     Zongwei  Zhou,  Jun  Han,  Yue-­‐Hsun  Lin,     Adrian  Perrig,  Virgil  Gligor     ECE  Department  and  CyLab,     Carnegie  Mellon  University                                   June  2013  

MoUvaUon   •  Deployment  of  cryptographic  systems  and   protocols  (e.g.,  HTTPS)  has  grown  rapidly  

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MoUvaUon   •  Key  management  is  a  fundamental  building   block  of  all  cryptosystems   •  Even  experts  fall  prey  to  inadequate  key   management  mechanisms   –  DigiNotar  CA:  keys  are  misused    to  issue   cerUficates  which  enabled  HTTPS  man-­‐in-­‐the-­‐ middle  a[acks   –  Stuxnet:  rogue  device  drivers  were  digitally  signed   by  keys  stolen  from  two  high-­‐tech  companies     3

Challenges   •  Fine-­‐grained  Key-­‐Usage  Control   –  Does  an  applicaUon  executed  by  a  user  have   permission  to  access  a  certain  key?  

•  Secure  System  AdministraUon   –  CommunicaUon  between  administrators  and   the  Key  Management  System  (KMS)  must  be   authenUcated   –  Stealing  authenUcaUon  credenUals  ?     –  Insider  a[acks?   4

ExisUng  SoluUons   •  Hardware  Security  Module  (HSMs)   –  Limited  control  of  key  usage   Tamper-­‐proof   physical  protecUon  

ApplicaUons  

Computer  

OperaUng   System  

HSM   5

ExisUng  SoluUons   •  Hardware  Security  Module  (HSMs)   –  Limited  control  of  key  usage   –  Large  TCB  for  system  administraUon   UI  Dev   UI  Dev  

Mgmt  Client  

Admin  Device  

Mgmt    Client   UI  Dev  

Computer  

OperaUng   System  

Management   Module  

HSM   6

ExisUng  SoluUons   SoHware-­‐only  SoluJons   •  Deployment  of  KMS  so_ware  on  commodity   servers   •  Large  TCB   –  Key  protecUon,  usage  control  and  administraUon   all  rely  on  untrustworthy  operaJng  system   services  (e.g.,  process  isolaUon,  file  system   permissions)   7

System  Goals   •  Small  and  Simple  TCB  dedicated  to  KSM   •  Cost-­‐effecUve   •  Secure  System  Bootstrap   •  Secure  System  AdministraUon   •  Fine-­‐grained  Key  Usage  Control  

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A[acker  Model   •  Malware  and  Malicious  Administrators   a[empt  to  leak,  compromise,  or  misuse   cryptographic  keys.     Malicious   Admins  

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System  Design   KISS  Client  

KISS  Server  

ApplicaJons  

Server   Bootstrap  

Key   Usage   Control  

Remote   AdministraUon   Client   Bootstrap   KISS  Manager   Trusted  Admin  Devices  (TADs)   10

Micro-­‐Hypervisor  Architecture   •  Unified  for  server,  client  and  manager   App   App   Untrusted     Commodity  OS  

KISS   So_ware  

KISS   ApplicaUon  

     KISS  Hypervisor   TAD   Other  KISS   machines  

USB   NIC  

Trusted     Path   Trusted  HW  

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DisUnct  Features   •  Secure  System  Bootstrap   •  Secure  System  AdministraUon   •  Fine-­‐grained  Key  Usage  Control  

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System  Bootstrap   •  Server  bootstrap  

Public   Key  

Private   Key  

TAD   Extended   Remote   ARestaJon   Protocol  

Server   SoHware  

KISS   Server  

TPM  

TAD  

TAD   13

Extended  Remote  A[estaUon   •  TPM  Quote  includes  KISS  hypervisor,  server   so_ware,  server  public  key,  TAD  public  key  list   •  Each  TAD  verifies:   –  Its  own  key  is  in  the  received  TAD  public  key  list     –  Length  of  the  key  list  =  #  of  TADs  

•  Minimum  administrator  effort   –  Checks  that  all  TADs  display  success  messages  

•  Security  Analysis  (e.g.,  Sybil  a[acks)   14

System  AdministraUon   •  e.g.,  remote  verificaUon  of  server  output   (1)  OUTPUT   &  Sig(OUTPUT)   from  KISS  server  

Sig(OUTPUT)   Hash(OUTPUT)   Manager   So_ware  

Untrusted   Commodity   OS  

Hash(OUTPUT)  

Hypervisor  

Display  

(3)  TAD  verifies  Sig(OUTPUT)   using  server  public  key,  and   display  Hash(OUTPUT)  

TAD   KISS   Manager  

(2)  Manager  display  OUTPUT  and   Hash(OUTPUT)  via  trusted  path  

(4)  Admin  uses  TAD  to  remotely   a[est  to  KISS  manager  so_ware   and  hyprevisor   (5)  Admin  confirms  that  two   Hash(OUTPUT)  match   15

System  AdministraUon   •  Small  and  Simple  TAD   –  So_ware:  a[estaUon,  msg  auth  and  bootstrap   –  Hardware:  bu[ons,  display  …   –  Usability:  hash  comparison   –  Used  for  local/remote  and  input/output  

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Key  Usage  Control   (2)  KISS  app  is  protected  and   verified  by  Hypervisor  

KISS   ApplicaUon  

Client   So_ware  

Untrusted   Commodity   OS  

Hypervisor   Display  

(1)  User  selects  the  KISS   applicaUon  to  execute   (4)  User  remotely  a[ests   to  the  Client  So_ware   and  Hypervisor  

UserV  

Auth   Dev  

Client   (3)  Client  So_ware   displays  app  informaUon   via  trusted  path  for  user   confirmaUon  

(5)  User  authenUcates   to  Client  so_ware  

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Key  Usage  Control     •  UserV  helps  defend  against  subtle  a[acks   –  e.g.,  stealing  authenUcaUon  credenUals,  or   sensiUve  user  input  

•  UserV  is  much  simpler  than  TAD   –  Only  performs  remote  a[estaUon   –  Does  not  store  any  secrets  

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Conclusion   •  A  key  management  system  architecture   leveraging  trusted  compuJng  techniques  on   commodity  computers   •  Small  TCB:  Micro-­‐hypervisor-­‐based  design  and   lightweight  administrator  devices.     •  Secure  system  bootstrap  and  administraUon,   fine-­‐grained  key  usage  control   –  Defend  against  malware  and  insider  a[acks   19

  Thanks!   [email protected]  

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