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##### Secure Communication

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**Secure Communication**P.V. Ananda Mohan FNAE, Fellow IEEE, FIETE ECIL, Bangalore**AGENDA**• Introduction • Current Scenario • Three Basic Requirements • Case studies • Conclusion**Where is Security needed?**• Military communications- media and terminal Encryption • Electronic Commerce • E-banking • Secure Storage • Internet Applications: e-mail etc • Wireless networks: GSM, CDMA, Wi fi, WiMAX, Blue Tooth**Devices and Types of Networks used for Communication**• Routers • LANs • Wireless devices • Virtual Private Networks (IPSec based) • SSL • PDAs (Personal digital assistants) • Storage Area Networks (SAN)**Algorithms and protocols are related to three basic domains**Authentication Encryption Hashing and Digital Signatures**Digital encryption**• Two techniques: • Stream ciphering : considered simple to implement, no error propagation, less latency • Block ciphering: considered complex to implement, smearing of whole blocks due to errors, latency of few blocks.**Stream ciphering**SEQUENCE GENERATOR Clear Data stream Ciphered data Stream = Masking = modulo 2 operation**Block ciphers**N bit input block K bit key N bit output block**E**Ti E Vi+1 E E Vi Ri ANSI X9.17 Random Number generator • Useful for generating session keys • DES can be used Ti is time stamp, Vi is seed and Ri is the output random number**A5 Stream cipher Algorithm of GSM**• LFSR= Linear Feedback Shift register IV LFSR 17 Clock LFSR 19 Clock control logic Clock IV IV LFSR 23 Clock Generated Sequence to mask speech**GSM authentication**• Authentication • Network sends RAND(128 bits) • Ki is secret key • Ki, RAND used with Algorithm A3 to produce SRES (32 bits) • A3 is operator dependent • Ki cannot be accessed by the user.**GSM Encryption**• Cipher Key Kc generated using Ki and RAND by algorithm A8 • Kc is 64 bits • Frame number (22bits) and Kc used with A5 to generate 114 bit cipher sequence • Speech is masked by cipher sequence and transmitted**RAND**RAND 128 Bits A3 A3 Ki Ki SRES (32 bits) SRES ? RAND A8 A8 Ki Ki Kc 64 bits Kc 64 bits Frame# Frame# Encrypted traffic A5 A5 GSM Authentication and encryption in a nutshell Handset Network SIM has Ki, Algo RAND**CDMA Encryption Methodology**RAND SSD generator ESN A-Key A-Key ESN RAND SSD Broadcast RAND generator CAVE CAVE SSDB SSDA SSDA SSDB Broadcast RAND CAVE CAVE CAVE CAVE ? 18 bit Sgnature check for authentication Long Code Long Code Data key Voice Scrambled Voice CEMA key ORYX ORYX Data Encrypted data CEMA CEMA Signalling Encrypted Signalling Messages**Future CDMA Encryption**• AES for Encryption • SHA for Hashing • AKA (Authentication and Key agreement protocol) • Kasumi Algorithm for Encryption and message security.**WEP 802.11 Wireless Network security**• Secret key shared between mobile and Access point • Standard does not say how the secret key is established • Single key shared by all laptops and access point! • Uses Integrity check field (IC) a CRC 32 to safeguard against modification in transit.**WEP 802.11 Wireless Network security**• Uses an IV (Initialization vector 24 bit) together with common shared secret key so that session key for RC4 changes. • RC4 is a stream cipher. • Too small repeats in 5 hours for a single user situation say for 1500 byte packets at 11Mb/s • In a multiple user scenario collision will be very frequent.**Blue tooth**• Three security modes • (a) no security (promiscuous mode) • (b) link level enforced (supports authentication and encryption, secret link key established based on entered PINs) • (c) Service level enforced (after channel is established )**48 bit**• SAFER (secure and fast encryption routine) 128 bit SAFER Algorithm**Blue Tooth Key generation and Encryption Methodology**Link Key • 1600 hops per second Encryption Offset Number (COF) EN-RAND 128 bit Kc Master Clock bits CLK 26-1 Algorithm to Modify Kc MAC Address 48 bit IV (Kc′) E0 Algorithm Kcipher Plain Text To medium**Blue Tooth Sequence generator**25 31 33 39**Tetra Security**• Mobile Radio Trunking • Different modes of operation (direct Mode of operation DMO etc ) • Authentication key K • Hierarchy of Keys: • Derived Ciphered key (DCK) • Common Cipher Key (CCK) generated by SWMI (Switching and Management infrastructure) • Group Cipher Key (GCK) • Modified Group Cipher Key = ECCK(GCK) • Static Cipher Key (SCK)- no prior authentication is needed (fixed pre-stored) • Uses IDEA (International Data Encryption Algorithm)**Identifies the user**Authentication code entered from keypad Algo K User Authentication key Identifies the handset Algo K Authentication code Identifies the handset and the user Algo K User Authentication key Tetra Authentication key generation**WiMAX security**• WiMAX World wide interoperability for Microwave Access (IEEE 802.16e) • Future PC will be with with three plug-ins (a) WCDMA for HSPA (high speed packet access) card for GSM users (b) CDMA 2000 for CDMA users ( c) card for WiMAX • Integrate WiFI with WiMAX using Montevino code**The MAC has a privacy sublayer than performs authentication,**key exchange and encryption of MPDUs.**SS (subscriber station) first must gain authorization to**access the system and a security association for its secondary management connection • Privacy and key management (PKM) protocol is used. • IP connectivity can then be established • User connections can be created using the MAC service.**Symmetric key encryption algorithms**• Data encryption standard(DES) • Triple DES • International data encryption algorithm (IDEA) • Blowfish • Many more • RIJNDAEL - the advanced encryption standard**General Features/Specifications**• Block length in bits • Key length in Bits • Rounds • Operations in Each round • Key Schedule for all rounds • Round Key generation • Decryption • Modes of operation • Any Weak Keys • Complexity / Execution time Benchmarks**IP**56 28 28 Expansion Rotate by number of bits as given in table in each round Rotate by number of bits as given in table in each round 48 bit sub-key1 Substitution Compression Permutation 48 bits Sub Key generation DES Structure 64 64 32 48 32 48 48 Permutation 32 One Round 32 32**Shift register**64-j bits j bits E Plain text Cipher text DES Modes 64 bit input Text block1 Text block2 Text block3 IV (Initialization Vector) E E E 56 bit key 64 bit output Cipher text blocks • ECB (Electronic Code Book) • CBC (Cipher Block chaining) Shift Register (64-J) bits J bits key J bits Discard 64-j bits Plain text j bits Cipher text j bits • CFB (Cipher feedback mode) • OFB (Output feedback) Encryption**Triple DES**C=EK1[DK2[EK1[P]]] • 112 bit key (caution: different K1 and K2!!!) E D E P C K1 K2 K1**Rijndael**Brand New!!! • Variable block length (128,192,256 bits) • Variable key length( 128,192 or 256 bits) • Block cipher • Data and key arranged as rows and columns • Byte level design • Suitable for DSP or Microprocessor based or ASIC implementation**Rijndael**• Four Rows • Nb columns : Nb = Block length/32 • Nk columns : Nk = Key length /32 • Number of rounds dependent on Nb and Nk: 4 6 8 4 10 12 14 6 12 12 14 8 14 14 14 Nb Nk**Rijndael**• Rounds shown in Table +1 needed • Each round consists of four operations: • 1)Byte Substitution • 2) Shift row • 3)Mix column • 4) Add Round key (modulo 2 bit by bit)**Rijndael**Substitute for each byte from a Rijndalel S-Box to get a new block Write data vertically in the memory Add Round Key Rotate Byte Followed by Mix column**Key Generation method**• Continue to get 44 words g**D**D S S U R K K U stands for Public R stands for Private S D D S R U R R U U Authentication Both Authentication and confidentiality Encryption and authentication Confidentiality Conventional encryption**Key distribution(contd..)**PUBLIC KEY AUTHORITY 4 1 5 2 3 A 6 B 7**Key distribution using certificates**CA KUa KUb CA CB CA B A CB**Authentication using RSA**• RSA ( Rivest- Shamir- Adleman) inventors • Two keys are used (public key and private key) Choose two large primes p and q. n = pq Choose e such that e and (p-1)(q-1) are relatively prime. Calculate d so that ed = 1 mod((p-1).(q-1)) Disclose d and n. Keep e safe with you. m = message Public Key = (e,n) Private Key = (d,n) Encryption c = me mod n Decryption m = cd mod n Modulo exponentiation is a complex task.**DIFFIE- HELLMAN KEY EXCHANGE**• Public values p and n. • A selects x and B selects y. k1= px mod n A B k2 = py mod n A computes k2x mod n B computes k1y mod n Both getpxy mod n**AUTHENTICATION BY DIGITAL SIGNATURES**M M -------- CK(M) K C COMPARE K**Y0**Y1 YN-1 F F F IV General Principle • F is a compression function • Yi are successive blocks in the input • If F is collision resistant, so is the Hash algorithm.