1 / 13

Network Security

Network Security. Section 3: Public Key, Digital Signature. New Algorithm Requirements. Definitions: E = Encryption Key D = Decryption Key New Requirements: D(E(P)) = P E #> D E not crack-able by “known texts” attack. ABCDEFGHI. ******************. P. Eb(P). Send to Bob. Eb. Ea.

isi
Download Presentation

Network Security

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Network Security Section 3: Public Key, Digital Signature

  2. New Algorithm Requirements • Definitions: • E = Encryption Key • D = Decryption Key • New Requirements: • D(E(P)) = P • E #> D • E not crack-able by “known texts” attack.

  3. ABCDEFGHI ****************** P Eb(P) Send to Bob Eb Ea Bob reads P ABCDEFGHI ****************** D(Eb(P)) Eb(P) Example Alice Ea, Da Bob Eb,Db

  4. RSA Adelman Shmir Rivest

  5. RSA • One of the public key algorithms • RSA Algorithm: • Chose two number p & q (1024bit) • n=p×q and z=(p-1)×(q-1) • Choose a number d that is relatively prime to z • e: e×d mod z = 1 • Divde P to blocks, 0 <= block length < n • C = Pe mod n • Exit. • OK. Where is the security location?

  6. OK! Lets finish cryptography algorithms HOOORAY! RSA Example • p = 3, q = 11 • n = 33, z = 20, d = 7, e = 3 No more cryptography algorithms PLEASE!

  7. Digital Signatures • Why do we use signatures? Authorization and Validity • What is the problem of signature in digital world? • Authorize sender • Message must be undeniable from sender’s prospective. • Receiver can not produce fake messages.

  8. Symmetric-Key Signatures • Store signature on valid institute (BB: Big Brother). • What is the problem of this method? Do you trust Big Brother?

  9. E(D(P)) = P D(E(P)) = P Public-Key Signatures Yes! How? • Be lost Da!! • Changing Da!! Can Alice evade message P? No! Why?

  10. Message Digests • Digital Signature do both authorization and confidentiality of message • Message Digests only authorize messages. • MD features: • Easy Calculation of MD(P) • MD(P) #> P • MD(P) # MD(Q) • MD(P) # MD(P+1)

  11. MD5 • MD5: 5th Message Digest. 128bit buffer • md5(apple) = 1f3870be274f6c49b3e31a0c6728957f

  12. SHA-1 • Secure Hash Algorithm • Developed by NSA • 160bit buffer

  13. The Birthday attack • Problem: If it is easy to find two random messages that map to the same signature then a birthday attack is easy • Example: the probability of 2 people having the same birthday in a group of 23 people is more than 0.5

More Related