1. Key management issues in PGP
Logan Wang
Key management issues in PGP

2. Public Key Cryptography
Is an encryption scheme that uses two keys
Can provide confidentiality, authentication, integrity and non- repudiation
Allows for more than just encryption/decryption
Digital signatures
Message integrity
Key exchange

3. Key management system Manages public keys that have been collected
Verifies the private key is legitimate
The way in which this is done is where PGP and PKI are different

4. PKI (Public Key Infrastructure)
Usually Hierarchical model
Certificates are public keys that have been signed by another entity
CA (Certification Authority) issues certificates
Root CA – self signed certificate
CRL – Certificate revocation list
X.509 certificate (not a complete list)
Subject and subject key
Issuer
Validity period
Certificate signature

5. PKI
Hierarchical system, relies on trustworthy CA

6. PGP (Pretty Good Privacy)
Created by Phil Zimmermann and released on the internet in 1991
Provides cryptographic protection of files and
PGP is now commercial, but there is free versions for non- commercial use
OpenPGP is a set of standards which describes the formats for encrypted messages, keys, and digital signatures.
GPG (GNU Privacy Guard) – open-source implementation of the standards set by OpenPGP, is the usual implementation found on Linux systems.

7. PGP – Key management Supports the Web Of Trust model
PGP software will generate keys for the user and help user manage them
A PGP Key consists of:
Owner’s name
the numerical value of the key
what the key is to be used for (e.g., for signing; for encryption)
the algorithm the key is to be used with, e.g. El Gamal; RSA; DSA
an expiration date

8. PGP – Key management Need to store lots of keys
Own private key (stored encrypted)
Own public key and public keys of others (stored in the open)
PGP software stores them in a file, called “keyring”
Keyring also stores certificates of other people which have been signed by the user
A public key stored in the user’s public keyring will have:
PGP key information
The trust, assigned by the user:
Full trust
Marginal trust
Untrusted
Unknown
Zero or more signatures

9. PGP – Web of trust
Community based trust model that entirely rely on its users
Everybody is a CA, every user can sign certificates
The idea of Web of trust is that you verify someone’s identity and decide to trust in them to trust people for you
Public key sharing done:
Physically
Key servers
or friends

10. Web of trust
Sources for images:
– graphed with sig2dot

11. Web of trust
William Stallings, Cryptography and Network Security, Principles and Practice,  Prentice Hall, 1999.

12. PGP - revocation To revoke a certificate:
User needs to generate the revocation information when they create the key
If key is lost, it’s impossible to generate the revocation information
Only user can revoke certificate
Telling everyone about the revocation:
Need to publish at all locations where the public key was provided
Hard to know who has it

13. PGP Key management issues
Lack of standards for identification verification
Allows each person control
Revocation notification
Need to maintain keys, web of trust, and to configure mail client
Can be tricked into receiving illegitimate keys
Quite complicated for the average user
Can be difficult for a new certificate to get in

14. Key signing party

15. PGP VS PKI Quick, easy to set up
Does not require entire infrastructure
Good for informal groups
Certificate has multiple levels of trust
Revocation is harder
Lack of standards
Distribute to a large amount of users
More control over subordinates
Certificate is either trusted or not trusted
Revocation is easier
Clear standards

16. PGP – secrecy issues No forward secrecy
Forward secrecy means that encrypted communications and sessions recorded in the past cannot be retrieved and decrypted, if the secret key or password is compromised in the future
Example: Alice and Bob establish communication, Eve is listening and stores all encrypted messages. Sometime later, Eve is able to obtain Bob’s private key. Eve can now read all of Bob’s past s. Additionally Eve has evidence in the form of a cryptographic digital signature that Alice was the one who sent the messages.
Not very private

17. Alternatives
Signal It uses the Internet to send one-to-one and group messages, which can include images and video messages, and make one-to-one voice and video calls. Signal uses standard cellular mobile numbers as identifiers, and uses end-to-end encryption to secure all communications to other Signal users. The applications include mechanisms by which users can independently verify the identity of their messaging correspondents and the integrity of the data channel. BUT it’s not

18. Solution Is there a need for one? Secrecy is important but…
PGP is reliable old technology that provides adequate encryption to those who need it
No new technology for has been developed and if that technology was to be developed can it be trusted and deployed

19. Questions?