Crypto U12 (part 1), crypto for mobile telecom

1. sent serial numbers in the clear
2. eavesdropping easy
3. cloning possible

1. designed by ETSI
   1. European Telecommunications Standards Institute
2. improved security over original

1. next step in evolution after GSM

Annotations:

• http://en.wikipedia.org/wiki/Zero-knowledge_proof#Abstract_example

1. mutual entity authentication
   1. supported by AKE (similar to GSM except additonal MAC key is generated)
   2. sequence # added for freshness and maintained by mobile device and base station
2. prevention of AKE triplet replay
   1. sequence #'s prevent replay
   2. roaming authentication upgraded to have quintlets
3. longer key lengths
4. publicly know algorithms
5. integrity of signalling data with a MAC

1. entity authentication of the user
2. confidentiality on radio path
3. anonymity on radio path
   1. prevents an attacker form linking the source of several calls
4. constraints
   1. not excessively strong
      1. export!
   2. do not add to much overhead
      1. especially on call setup

1. fully symmetric architecture
   1. GSM closed system
   2. fast
2. stream cipher
   1. noisy comm channel
3. fixed encryption algorithms
4. proprietary algorithms
   1. closed system
   2. ETSI has crypto expertise
   3. performance

1. subscriber identification module (SIM)
   1. has international mobile subscriber identity
      1. maps user to phone
   2. has unique 128 bit crypto key used for all crypto services
2. AKE (authentication and key establishment)
   1. uses dynamic password scheme
   2. protocols
      1. A3
         1. challenge response protocol
      2. A8
         1. generate encryption key
   3. not shared with other access providers
   4. special roaming scheme
3. comm encryption
   1. service shared with other mobile networks
   2. Uses standard A5/1
      1. 64 bit key, stream cipher

1. popular implementation of A3 and A8 was COMP 128
   1. designs leadked and weaknesses found
2. A5/1 reverse engineered
   1. powerful attacks developed
3. effective because it addressed cloning and eavesdropping