## 3. Public Key, Key Exchange and Digital Certs[Home] The key concepts are: **Public Key**: Basics, RSA, Elliptic Curve and ElGamal.**Key exchange**: Diffie-Hellman, Diffie-Hellman Weaknesses, and Passing Key Using Public Key.**Digital Certifications**: Usage, formats, and PKI.
## What you should know at the end of unit?- Explain how public key provides both privacy and identity verification.
**Where would I find this info?**This unit explains public key.
- Understand how the RSA process works, with a simple example.
- Understand how the Diffie-Hellman process works, with a simple example
- Understands how the private key is used to check the identity of the sender, and how public key is used to preserve the privacy of the message.
- Explain how the e and d values are determined within the RSA method.
**Where would I find this info?**There are some examples here.
## Presentations- Week 3 Presentation (PDF) - Public Key Encryption: here
- Week 3 Presentation (video) - Public Key Encryption: here
- Week 3 Presentation (PDF) - Key Exchange: here
- Week 3 Presentation (video) - Key Exchange: here
- Week 3 Presentation (PDF) - Digital Certs: here
- Week 3 Presentation (video) - Digital Certs: here
## Lab## Tests**Take Test (Crypto 2):**here
## Sample Exam QuestionsThe following are sample questions for public key: - Bob selects a p value of 7 and a q value of 9, but he cannot get his RSA encryption to work. What is the problem?
- Bob has selected a p value of 11 and a q value of 7. Which of the following are possible encryption keys: (5,77), (3,77), (9,77), (11,77), and (24,77).
- Bob and Alice decide to use RSA encryption to send secure email, where Bob uses Alice's public key to encrypt, and she uses her private key to decrypt. What is the main problem caused with this, as apposed to using symmetric encryption?
- Bob tells Alice that she should send her private key in order that he should encrypt something for her. Outline the main problem caused by this.
- Security professionals say that RSA keys of over 1,024 bits are secure. What is the core protection against the RSA method being cracked for keys of 1,024 bits and more.
- Bob says he has had a look at a few RSA public key and he says that the ones he looked at where all the same. Is he right? If so, what makes public keys different?
**Research:**Netscape had to comply with an export embargo on the size of the keys which can be used for RSA. Which major vulnerabilities have resulted?- Bob and Alice get into a debate about the size of the d and e values in the RSA encryption key. Bob says that, in real-life keys, the length of the e value in (e,n) is normally about the same size as the d value (d,n). Alice disagrees. Who is correct?
**Where would I find this info?**Have a look at some practical examples: Here
The following are sample questions for key exchange: - Eve listens to Bob and Alice's communcication for their Diffie-Hellman handshaking. In order to generate the same key as Bob and Alice, which values will Eve try to determine, and how is it likely to be difficult to gain these?
- For the following key exchanges, Bob generates x, and Alice generates y. Prove the shared key. [Examples]
- x=3, y=4, G=4 and N=7. Share=1.
- x=6, y=15, G=5 and N=23. Share=2.
- x=5, y=7, G=10 and N=541. Share=193.
- x=6, y=15, G=5 and N=23. Share=2.
- x=7, y=7, G=5 and N=11. Share=9.
- x=7, y=9, G=8 and N=13. Share=5.
- x=5, y=4, G=2969 and N=9929. Share=8106.
- x=6, y=5, G=3881 and N=125. Share=792.
- x=3, y=4, G=3623 and N=1153. Share=939.
- Why are Forward Security and Ephemeral so important for the security of your keys?
The following are sample questions on digital certificates: - Bob has just produced a key pair, in a Base-64 format, and now wants to send this to Alice. What advice would you give him on sending the key pair to Alice?
**Where would I find this info?**Have a think about the certificate which is distributed. You can observe it here.
- Bob sends an encrypted message to Alice, and also sends his digital certificate to Alice to prove his identity. How does Alice prove that it is Bob who sent the message?
## Examples## Any questions?Contact Bill Skype: billatnapier |