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A5 GSM Encryption Kingdom Special Operations SJS-KW Ki.

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Presentation on theme: "A5 GSM Encryption Kingdom Special Operations SJS-KW Ki."— Presentation transcript:

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2 A5 GSM Encryption Kingdom Special Operations SJS-KW Ki

3 Encryption key words n Symmetric algorithms Block ciphersBlock ciphers Stream ciphersStream ciphers n Public key algorithms n One-way hash functions Ki

4 GSM Security Features n Distribution of security features SIM=SIM= –A3 & A8 IMSI Ki TMSI/LAI Kc/CKSN MS=MS= –A5 BS=BS= –A5 Kc [TMSI/IMSI = VLR] MSSIMBSMSC

5 GSM Security Features n Authentication MS and network compute SRES from RANDMS and network compute SRES from RAND Network [VLR] compares resultsNetwork [VLR] compares results MS BS RAND =? SRES = A3(RAND, Ki) Authentication Successful Fail Ki

6 GSM Security Features n Key generation K c is computed from RANDK c is computed from RAND MS BS RAND Kc = A8(RAND, Ki) KcKcKcKc KcKcKcKc A5A5A5A5 DATA TDMA frame TDMA frame Ki

7 How A5 GSM Encryption run n Three clock controlled LFSRs n Feedback polynomials have degree 19,23, and 22 (their sum is 64) n The 64-bit cipher key initializes the LFSRs n 22-bit TDMA frame number is fed in n Two 114-bit key streams (uplink and downlink) Ki

8 A5 GSM Encryption of data REG_FILE 9x16 Bit LFSR CONTROL CIP_SEQ_RAM 30x8 Bit done start cip_key:86 A5 mode cip_bit clk_en wr add data ld_key data sel cip_add clk reset sel cip_data Ki AT MS* AT BTS*

9 A5 GSM x3 register Encryption n LFSRs R1 : 19 R2 : 23 R3 : 22 Out Func Clock Control Frame: 22Kc : 64 Ki

10 A5 GSM Encryption FSM n CONTROL done idle load key roll 100 blk_1 blk_2 Ki

11 A5 GSM Encryption n Registers TMDA Frame number 22BitsTMDA Frame number 22Bits Kc Cipher Key 64Kc Cipher Key 64 Ki

12 A5.1 vs. A5.2 n Export restrictions A5.1 algorithm is not exportable to designated countries [Only In Europe]A5.1 algorithm is not exportable to designated countries [Only In Europe] A5.2 algorithm modified for exportA5.2 algorithm modified for export n Implementation Differences A5.1 A5.2 Output functionOutput function Clock controlClock control Control unitControl unit Ki


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