1. Network Security

3. Cryptography Cryptography functions Secret key (e.g., DES) Public key (e.g., RSA) Message digest (e.g., MD5) Security services Privacy: preventing unauthorized release of information Authentication: verifying identity of the remote participant Integrity: making sure message has not been altered

4. DES Data Encryption Standard (DES) 56 bit key, insecure Triple DES is secure, but supplanted by AES Advanced Encryption Standard (AES) Specified for US Government contracts Neither are provably secure

5. Encryption Algorithms Private Key (DES) 64-bit key (56-bits + 8-bit parity) 16 rounds Round 1 Round 2 Round 16... plain text Initial Permutation Final Permutation 56bit Key Encrypt w/ Secret Key Decrypt w/ Secret Key plaintext ciphertext

6. Each round Function F and generation of K i for each round not shown Repeat for larger messages L i -1 R i 1 L i R i F + i K

7. AES AES operates on a 4×4 array of bytes, termed the statebytes For encryption, each round of AES consists of four stages: AddRoundKey - each byte of the state is combined with the derived cipher key SubBytes - a non-linear substitution step where each byte is replaced with another according to a lookup table.lookup table ShiftRows - a transposition step where each row of the state is shifted cyclically a certain number of steps. MixColumns - a mixing operation which operates on the columns of the state, combining the four bytes in each column using a linear transformation.

8. RSA Public key/Private Key Provably secure (NP-Complete type proof) Slow

9. Multiplicative inverse for public key With n=7 4*2 mod 7 = 1 4 and 2 are multiplicative inverses mod 7 4*3 mod 7 = 12 mod 7 = 5 2*5 mod 7 = 10 mod 7 = 3 If you multiply any number by 4, take the result and multiply it by 2, you will get the original number back

10. Encryption & Decryption c = m e mod n m = c d mod n Encrypt w/ Public Key Decrypt w/ Private Key plaintext ciphertext

11. Public Key (RSA) Based on multiplicative group operations Generate a public and private key choose two large prime numbers p and q (each 256 bits) multiply p and q together to get n (at most 512 bits) choose the encryption key e, such that e and (p-1) x (q-1) are relatively prime two numbers are relatively prime if they have no common factor greater than one. compute decryption key d such that d = e -1 mod((p-1)*(q-1)) construct public key as construct private key as discard (do not disclose) original primes p and q

12. Example p=5, q=11, n=p*q=55, m=message=9, (p-1)(q-1)=40, e=23 and (p-1)*(q-1) are relatively prime We want d*e=1mod 40, d*23=1mod40 You can try all values less than 40 23*2=46=6mod40, 23*3=69=29mod40, 23*4=92=12mod40, 23*5=115=35mod40, 23*6=138=18mod40 23*7=161=1mod40, d=7 For a message m=9 c=m e modn=9 23 mod55 How big is this? = 9 10 mod55*9 13 mod55= 1*14 mod 55 m=c d modn=14 7 mod55=105413504mod55=9

13. Breaking RSA 1977 challenge to break 430-bit message Estimated 40 Quadrillion years to factor large composites April 1994 broken with 5000 MIP-years of CPU Breakage can be easier if something is known about the key generation (time of day)

14. Message Digest Cryptographic checksum: just as a regular checksum protects the receiver from accidental changes to the message, a cryptographic checksum protects the receiver from malicious changes to the message.

15. One-way function: given a cryptographic checksum for a message, it is virtually impossible to figure out what message produced that checksum; it is not computationally feasible to find two messages that hash to the same cryptographic checksum.

16. Relevance: if you are given a checksum for a message and you are able to compute exactly the same checksum for that message, then it is highly likely this message produced the checksum you were given.

17. Speed 175MHz DEC Alpha Custom Hardware Sonicwall claims 54Mbps DES3 in hardware ssl.com advertises 75Mbps DES today Md5 1.27Gbps SHA 1.02Gbps RSA 400 keys/second

18. Message Integrity Protocols Digital signature using RSA special case of a message integrity where the code can only have been generated by one participant compute signature with private key and verify with public key

19. Making Signatures Compute checksum of signed document Encrypt checksum, time and date, and other information using private key Attach digital signature to end of document Optionally, encrypt signed document with receiver’s public key

20. Checking Signatures Decrypt signed document, if necessary, using private key Decrypt digital signature using public key Verify checksum for document Display the time and date of the document

21. Certificates Certified Entity CA Verifier Decrypt senders public key using CA- publickey Albert Levi Albert Levi Register with CA, send client Public Key CA-Publickey and Certificate with RSA(client Public Key,CA-privatekey) Certificate

22. TLS,SSL,HTTPS Transport Layer Security, Secure Socket Layer

23. SSL Each browser is configured with a root CA When a session is initiated, server and client agree on security capabilities. (most clients are 40 bit encryption, but 128 bit encryption is available on many strong servers The server is authenticated by the certificate authority Using the server public key from the CA, the client sends a DES key to the server The DES key is used to encrypt the session

24. IPSEC Optional in IPv4, mandatory in IPv6 Data Confidentiality---The IPSec sender can encrypt packets before transmitting them across a network. Data Integrity---The IPSec receiver can authenticate packets sent by the IPSec sender to ensure that the data has not been altered during transmission. Data Origin Authentication---The IPSec receiver can authenticate the source of the IPSec packets sent. This service is dependent upon the data integrity service. Anti-Replay---The IPSec receiver can detect and reject replayed packets.