IntroSec

Added a few words on Cryptocurrencies.
Beginning with privacy.

1 files changed, 51 insertions, 0 deletions

diff --git a/en_GB/Introduction to Information Security/introduction_to_information_security.md b/en_GB/Introduction to Information Security/introduction_to_information_security.md
index 947b427..60774c8 100644
--- a/en_GB/Introduction to Information Security/introduction_to_information_security.md
+++ b/en_GB/Introduction to Information Security/introduction_to_information_security.md
@@ -250,6 +250,11 @@ In that case, there could be a program the user has execute rights on, containin
 Those programs are called *set UID* (SUID) and *set GID* (SGID) programs. They set the *effective UID/GID pair* to the ones required
 to access the file (they might have to be created) and reset them on exit. Be careful with *SUID to Root* programs!
 
+### Android
+
+In android, each app has an AID. Normal privileged apps have an AID above 10000, high privileged ones have the range 1000-1999.
+For each app, a new user is created. Every app runs in its own JVM, which runs on the underlying Linux with AID as UID.
+
 ## Encryption
 
 ### Kerckhoffs' Principle
@@ -379,6 +384,52 @@ Infrastructure providing the service of public key distribution.
   Medium. CA checks same as *DV* + company identity checked by third parties.
 - Extended Validation SSL Certificate (EV cert)  
   Expensive. CA checks same as *OV* + official record matching.
+  
+## Cryptocurrencies
+
+### Ledger
+
+A *ledger* keeps a log of all transactions and fulfills the following security services:
+
+- Log entries cannot be modified
+- Log entries cannot be deleted
+- Log entries cannot be reordered
+
+Ledgers can be centralized (trusted third party) or distributed.
+
+### Byzantine Generals Problem
+
+Byzantine generals: *n* generals, *m* of which are traitors.  
+*Practical Byzantine Fault Tolerance (PBFT)*: True consensus is possible, if
+
+$$
+\text{n} \geq 3 \cdot m + 1
+$$,
+with *n* replicas and *m* faulty nodes.  
+As long as this holds true, the primary can assure that enough replicas are forwarding his message correctly.
+
+#### Protocol
+
+1. Client sends authenticated request to all replicas.
+2. Primary *p* sends autheticated *pre-prepare* to all backups.
+3. Every backup *i* agreeing, sends a *prepare* to all other replicas.
+4. Once a replica has $2 \cdot \text{m}$ prepares collected from other replicas, it sends *commit* to all other replicas.
+5. Once a replica has $2 \cdot \text{m} + 1$ commits collected from other replicas, its sends *reply* to the client.
+6. Client waits for at least $\text{m} + 1$ replies in order to consider the request as valid.
+
+All messages are authenticated and signed by the sender.
+
+## Privacy
+
+### Foundation
+
+Privacy is based on the *Universal Declaration of Human Rights*. No one shall be interfered in his private life.
+
+### Dimensions
+
+- Surveillance: What do others know about you?
+- Ownership: What may others do with your data?
+- Nuisance: Right to be let alone
 
 ## Crypto Analysis