<img src='https://cdn.pixabay.com/photo/2015/12/13/15/32/cryptographic-1091257_960_720.jpg'>
_<h5>Image from google images, labeled for reuse: <a href='https://www.google.com/search?q=google+images&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjeq4_g1tnRAhWi6YMKHUakALAQ_AUICCgB&biw=1366&bih=598#tbs=sur:fc&tbm=isch&q=encryption+images&imgrc=30uiCe2zjtYfJM%3A'>Original Link</a></h5>_

<h5>Note:</h5> This article is of the form Wikipedia Report and it is a method used to facilitate the assimilation of researched information into a working understanding which is analogous to the classic Book Report from grade school. I won't necessarily be using Wikipedia exclusively but of course it is the starting point of choice for quick research, (If you have an opinion about a better method please let me know, I am endeavoring to ingrain good researching habits & any assistance would be greatly appreciated) simply because of the sheer scope of topics covered.

<h5>Cipher Block Chaining (CBC)</h5>

What is _Cipher Block Chaining_? Well, first off what is _Block Chaining_?

From <a href='https://en.wikipedia.org/wiki/Blockchain_(database)'>Wiki</a>--A **blockchain** (originally **block chain**) is a distributed database, where each sequential data block in the chain has a timestamp and a link to the previous block. 

<img src='https://upload.wikimedia.org/wikipedia/commons/thumb/9/98/Blockchain.svg/150px-Blockchain.svg.png'>
_<h5>Figure 1: blockchain (From <a href='https://en.wikipedia.org/wiki/Blockchain_(database)'>Wiki</a></h5>_

  The article goes on to say that **blockchains** are inherently resistant to data modification, once the data is written is cannot be modified (it is _set in stone_ if you will). There is a caveat to this: occasionally _concurrent validation_ can occur, resulting in a fork, and which ever branch ends up becoming the predominant one causes the other branch to be _orphaned_ (a feat exponentially more likely with increasing chain size of the branch). Eventually the blocks which become orphaned are culled from the blockchain, therefore it is **not** always _set in stone_. (From an article on bitcoin this is sometimes done on purpose as a result of a type of hacking/attack called _transaction reversing_; however this requires serious hashing power).

  The **blockchain** data structure allows for decentralized ledger keeping and solves the problem of double-spending. The use of a blockchain in software architecture is an example of using a _distributed database_. The chain primarily grows linearly with occasional forking, and subsequent orphaning. Loss of communication between computers participating in the blockchain can cause forking as well, which would result in a great deal of data loss when one of these long chains became orphaned after re-uniting the segregated computers. This is the technological basis for **bitcoin** (and **Steemit** as well). 

Interestingly enough the blocks themselves are composed of individual transactions encoded in a **Merkel Tree** data structure. (Okay this is probably why my colleague asked me to research **Merkel Tree** and **Cipher Block Chaining**)

Okay, now on to **Cipher Block Chaining**: 

_Cipher block chaining_--Would this would be a **blockchain** utilizing a **block cipher**? (which is a form of text encryption where all the contiguous bits in a block are operated on by a **cipher key** and an **algorithm** at once, as opposed to bit by bit, as in a **stream cipher** [<a href='http://searchsecurity.techtarget.com/definition/block-cipher'>Ref 1</a>]) 

  Actually, no... it isn't as simple as concatenating terms and nesting definitions in this case. Rather it seems a more correct way of describing this is that is is _a mode of operation_ of a _block cipher_, where an **initialization vector** of a certain length is employed, it also characteristically uses a _chaining mechanism_ that makes the decryption of a block of **cipher text**  to depend on all preceding **cipher text** blocks. [<a href='http://searchsecurity.techtarget.com/definition/cipher-block-chaining'>Ref 2</a>] The error of a single bit affects the decryption of all later blocks, and decryption of the blocks in the wrong order results in data corruption. During encryption, each plaintext block is **XOR**'d with the immediately preceding block, then encrypted...

<img src='https://upload.wikimedia.org/wikipedia/commons/thumb/8/80/CBC_encryption.svg/601px-CBC_encryption.svg.png'>
_<h5>Figure 2: CBC Encryption (from <a href='https://upload.wikimedia.org/wikipedia/commons/thumb/8/80/CBC_encryption.svg/601px-CBC_encryption.svg.png'>Wiki</a></h5>_

<img src='https://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/CBC_decryption.svg/601px-CBC_decryption.svg.png'>
_<h5>Figure 3: CBC Decryption (from <a href='https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CBC'>Wiki</a></h5>_

  Okay, well... I would like to clear up the definitions of the emboldened  text (which isn't already mentioned), in a list format:

1. **Initialization Vector**--From <a href='https://en.wikipedia.org/wiki/Initialization_vector'>Wiki</a>
In cryptography, an initialization vector (IV) or starting variable (SV) is a fixed-size input to a cryptographic primitive that is typically required to be random or pseudorandom. Randomization is crucial for encryption schemes to achieve semantic security, a property whereby repeated usage of the scheme under the same key does not allow an attacker to infer relationships between segments of the encrypted message. For block ciphers, the use of an IV is described by the modes of operation. Randomization is also required for other primitives, such as universal hash functions and message authentication codes based thereon.
2. **XOR**--From [<a href='http://whatis.techtarget.com/definition/logic-gate-AND-OR-XOR-NOT-NAND-NOR-and-XNOR'>Ref 3</a>]
This is just like logical **OR** except in the case of **true** XOR **true**, which evaluates to **false**.
3. **Cipher Text**
This is the original text data which becomes encrypted into blocks.
4.  **Cipher Key**--From <a href='https://en.wikipedia.org/wiki/Cipher'>Wiki</a>
The operation of a cipher usually depends on a piece of auxiliary information, called a key (or, in traditional NSA parlance, a cryptovariable). The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using a cipher to encrypt a message. Without knowledge of the key, it should be extremely difficult, if not impossible, to decrypt the resulting ciphertext into readable plaintext.

  Okay, well now I feel that I understand the ideas a bit better, at least enough to implement them with reference back the schematic figures, :-). I feel that the _disambiguation_ resulting from including the paraphrased description of _blockchain_ outweighs the cluttering effect of it being only _somewhat related_ to **CBC** (**Cipher Block Chaining**). 

  In conclusion, I now understand these technologies better, and I hope I didn't make too many mistakes, Thank You for reading this and please comment if I got something wrong... Until next time!