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312/ciphers.md

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-# Block Ciphers
+Active v Passive Attacks
+========================
 
-The main concept here is twofold:
+Base Definitions
+----------------
 
-* we take _blocks_ of data and cipher the _blocks_
-* A given key is actually used to generate recursive keys to be further used on the data itself
+Passive: compromising a system but not necessarily doing anything apart
+from *watching*
 
+Active: compromising a system while doing something to the system apart
+from infiltrating it
 
-_bs example ahead_
+Loosely speaking
+----------------
 
-Say we have a key 7 and some data 123456.
-We take the whole data set and chunk it into blocks(for example): 12 34 56.
+*Passive* can be just like listening in on a conversation(eavesdropping)
+where *active* is like jumping into the conversation and trying to do
+something to it.
 
-Let's say our function here is to just add 7 to each block so we do the first step: 
+When/How would either happen?
+-----------------------------
 
-```
-12 + 7 = 19
-Unlike other ciphers we don't reuse 7; instead we use the new thing as both the new key and part of our cipher text
+If the result of an attack is to actually trigger some code to run then
+usually we need to first gather the information required to understand
+how to make that happen. The reasoning is straightforward: if you don't
+know how some system works then it's much harder to exploit that system.
 
-19 + 34 = 53
-Cipher: 1953..
-
-53 + 56 = 109 <= let's pretend that this rolls over 99 and back to 00
-          09  <= like this
-
-Final cipher: 195309
-```
-
-_It should be noted that in practice these functions usually take in huge keys and blocks_.
-
-> Deciphering
-
-Start from the back of the cipher not the front; if we used and xor function scheme (which is a symmetrical function) we would simply just xor the last block by itself and thus perform the same encryption scheme but in reverse.
-
-Example::Encryption
-
-```
-Key: 110
-Function scheme: xor
-Data: 101 001 111
-
-101 011 010
-110 001 111
-
-011 010 101 <= encrypted
-
-```
-
-Example::Decryption
-
-```
-Ciphered: 011 010 101
-Function scheme: xor
-
-...
-```
-
-# Feistal Cipher
-
-Two main components:
-
-1. each _thing_ in the data to cipher is replaced by a _ciphered thing_
-
-2. nothing is added or deleted or replaced in sequence, instead the order of _things_ is changed.
-
-Basically imagine that every _type of thing_ in our data maps to some other _type of thing/thing_ in the data and thus become swapped/reordered.
-
-# DES - Data Encryption Standard
-
-Widely used until about 2001 when AES surpassed it as the newer(ish(kinda)) standard.
-
-DEA was the actual algorithm tho:
-
-* 64 bit blocks
-* 56 bit keys
-* turns a 64-bit input into a 64-bit output (wew)
-* Steps in reverse also reverse the encryption itself
+Random example: Using a keylogger to log keystroke before sending those
+logs to a server for processing could be a passive attack since you're
+still in a *gathering data* sort of mode. Finally using that data to
+trying logging into some service would be the active portion of a
+full-scale attack.