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Semester 1/Computer Systems Internals & Linux/Week 6/Week 6 Computer Systems.md

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+## Lecture 1 (10:00)
+
+### Caesar Cipher
+
+#### Dictionary
+
+- Precalculate encrypted versions of likely words, and when one appears, test the key on the whole message.
+
+#### Plaintext
+
+- If you can see certain English commonalities in the cipher, you can make an educated guess. ex. If one letter appears alone, it is most likely an "A" or an "I".
+
+### DES - Data Encryption Standard
+
+- Cascaded Transposition.
+- Substitution Ciphers.
+- Initially proposed as 128-bit, US Gov enforced 56-bit. Wonder why????
+	- `2^128` - `3.4x10^38` combinations. `5x10^19` years to do half at 100 billion keys per second.
+	- `1^56` - `7.2x10^16` combinations. `4` days to do half at 100 billion keys per second.
+
+### Current State
+
+- (1999) Triple DES - 112bit -> 128bit standard
+- (2002) AES - 128bit -> 256bit
+
+# Assessment
+
+## 4pm 27th Nov Deadline
+
+- 50% of mark, questions on blackboard