Blockchain is essentially a decentralized algorithm for distributed storage and processing , using a non immutable data structures and securing them with signatures and keys . These sequential chain of records called blocks , can contains almost anything from timestamped transactions , metadata , contracts , files etc just as long as they are chained using hash pointers to previous blocks  .

what is  a hash ?

function f (x) = y , takes an i/o and give a determined o/p . example heaxadecimeal output of my name , md5(altanai bisht) = 2b9e76d57842ebafaf19fd33bb3573a3.

These are irreversible ie one cant find the i/p from o/p . For this u need to try every combination using brute force. Hence these are generally used for cross verification without revealing the information itself .

Who are miners ?

-tbd –

Application of block chain :

Market analysts and industry specialist have said that block-chain is a revolutionizing technology which will create a decentralized network for not just currency exchange but also many other aspects such as double spent problem , universal identities  , document management etc . Example : Bitcoin protocol , which contains a full record of every transaction ever executed with the currency at any time in past. It is also a solution to problem like black – money , double spending , tax evasions etc. Other areas include:

• Decentralizing document keeping such as government records , digital assets , equity information , medical and health records etc . The system also provide data ownership and Intellectual property protection .
• Fintech as AML( Anti money laundering) , eKYC ( Know Your customer )  , epay , loans, stock trading .
• Smart contracts such as in ethereum . Allows to keep program code that would execute on an event.
• Shared economy for a p2p payment system .
• Crowdfunding , works on paradigm of  token owner’s voting and cooperation in decisions for crowd-sourced venture capital funds .
• Micro payments / fractional concurrency for small amounts suits power selling and buying  such as on solar renewable power micro grid

Since a block chain is a ledger of facts shared across many peer nodes , all communication and inter node transaction uses the power of crypto to authenticate  each other and validate each others requests from the genesis block .

what is a genesis block ?

First block of blockchain which needs to be hard-coded into software . It is the only block which does not reference a previous block .

As any peer wants to add a fact to the ledger , a consensus needs to be obtained from the network. This way of network agreement ensures that fraudulent behavior is prevented .

Example : bitcoin’s genesis block

01000000 - version
0000000000000000000000000000000000000000000000000000000000000000 - prev block
3BA3EDFD7A7B12B27AC72C3E67768F617FC81BC3888A51323A9FB8AA4B1E5E4A - merkle root
29AB5F49 - timestamp
FFFF001D - bits
1DAC2B7C - nonce
01 - number of transactions
01000000 - version
01 - input
0000000000000000000000000000000000000000000000000000000000000000FFFFFFFF - prev output
4D - script length
04FFFF001D0104455468652054696D65732030332F4A616E2F32303039204368616E63656C6C6F72206F6E206272696E6B206F66207365636F6E64206261696C6F757420666F722062616E6B73 - scriptsig
FFFFFFFF - sequence
01 - outputs
00F2052A01000000 - 50 BTC
43 - pk_script length
4104678AFDB0FE5548271967F1A67130B7105CD6A828E03909A67962E0EA1F61DEB649F6BC3F4CEF38C4F35504E51EC112DE5C384DF7BA0B8D578A4C702B6BF11D5FAC - pk_script
00000000 - lock time

Forks 

There is only one path from top block on chain to genesis root , however  there can many forks upwards from genesis block . It is so because blocks may be created within a short span of time or be  under processing . One of the two block will be added to main chain and other will be orphaned or added to pool of queued transactions or even be lost.

Steps to Programming a simple block-chain application :

Lets assume we are creating a block chain for call records.

Create a class for member function and variables

define variable chain as an array and transactions as array as well

create functions for createNewBlock() , createNewTranscation() , fetchLastBlock() ,

boolean isBlockValid ( newBlock , oldBlock) – checks if the oldblocks index is sequentially aligned with new block and whether old blocks hash is equal to new blocks previous hash . Also calculates whether hash of new block is actually same as the supplied hash value in new block ( give  below) .

hashBlock( block ) –  to create the hashes we need to add in block. Basically a SHA 256 hash of concatenated arguments as index, timestamp, message , previous hash and a nonce . example pseudo code :

Consensus Algorithms

All block-chains a\re deterministic state machines and transactions act upon them . Consensus filters out the invalid ones and reaches on agreement with valid ones.

DPOS (Delegated Proof of Stake)

A consensus algorithm used for electing producers and scheduling them in a fair and democratic way . It works on the simple principle that longest chain wins therefore incases of multiple forks or network disruption also , if an honest peer finds out a  valid strictly longer chain  , it will switch from its current fork to the longer chain. We assume that in all conditions ,  no other chain forked can be longer if 2/3 of producers are honest as 2/3 + 1 confirmations are required .

In crypto we trust !

Block chain is primarily 3 things : p2p network, public key cryptography and distributed consensus .

The security and accountability of such a system is managed via mass surveillance of transactions and cryptographic evidence. Ensures that blocks are always in chronological order  since meddling with the blocks will change the hash for preceding blocks

Verification of block uses ECDSA ( Elliptic Curve Digital Signature Algorithm ) to ensure that tokens are spend by their rightful owners only.

An ellipsis is a derived from the second degree equation like ax^2 + bcy + cy^2 + dx + ey +f =0 . Depending on attributes this could be hyperbola , parabola or even a circle . However elliptic curve cryptography uses a third degree equation  from either a pseudo -random curve  ( such as over prime  fields y^2=x^3+ax+b or binary fields y^2 + xy = x^3 + ax^2 + b ) or a special curve .

what is ECDSA ?

There are 2 types of auth schemes : Symmetric , relying on shared secret key and Asymmetric relying on private public keys . ECDSA is a asymmetric authentication scheme where in addition to sender and receiver , even 3rd party systems can be authenticated .  In this the sender uses his private key to sign the message and receiver uses the senders public key to verify the message’s signature .

Difficulty 

While publishing a block with pending facts  to be appended to a chain , the owner sends it to other nodes for confirmation on its validity. Once its approved , other nodes called miners add it to their copy of chains. However the new block has to be published after fixed time interval for fraud prevention ( example :  bitcoin blocks are published every 10 mins on avg ) .  This duration is dynamically recalculated as the network miners grow or shrink . A difficulty is a number metric that represents how difficult is it to find a hash for given target.

• To force increase time for calculating the matching hash  , difficulty is increased for miners work harder and take longer to earn the block reward .
• While  in case of  less miner participation , the block difficulty level is made lower

Ref :

• https://www.quora.com/What-is-a-block-chain-algorithm
• https://learncryptography.com/hash-functions/what-are-hash-functions
• https://en.bitcoin.it/wiki/Genesis_block
• https://www.maximintegrated.com/en/app-notes/index.mvp/id/5767
• https://cryptovoices.com/block-difficulty/

Automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is a small object that can be attached to or incorporated into a product, animal, or person. RFID tags contain silicon chips and antennas to enable them to receive and respond to radio-frequency queries from an RFID transceiver. Passive tags require no internal power source, whereas active tags require a power source.

The purpose of an RFID system is to enable data to be transmitted by a mobile device, called a tag, which is read by an RFID reader and processed according to the needs of a particular application.

The use of RFID in tracking and access applications first appeared during the 1980s. RFID quickly gained attention because of its ability to track moving objects. As the technology is refined, more pervasive and possibly invasive uses for RFID tags are in the works.

Operation

In a typical RFID system, individual objects are equipped with a small, inexpensive tag. The tag contains a transponder with a digital memory chip that is given a unique electronic product code.

The interrogator, an antenna packaged with a transceiver and decoder, emits a signal activating the RFID tag so it can read and write data to it.

When an RFID tag passes through the electromagnetic zone, it detects the reader’s activation signal. The reader decodes the data encoded in the tag’s integrated circuit (silicon chip) and the data is passed to the host computer.

Frequencies:

Low-frequency (LF: 125 – 134.2 kHz and 140 – 148.5 kHz)

A low-frequency device typically provides slower data transfer and must work at closer distances to an object. Relative speed of the tag moving on a production line past an interrogation unit is approximately 20 miles an hour.

High-frequency (HF: 13.56 MHz) RFID tags can be used globally without a license.

High-frequency devices can work at distances up to 250 feet and at relative speeds greater than 150 miles per hour.

Ultra-high-frequency (UHF: 868 MHz-928 MHz) cannot be used globally as there is no single global standard.

High-frequency passive systems are typically in the UHF range — i.e. from 500 MHz and above, but usually in the 900 MHz band to 2.5 GHz. These systems are particularly well suited to the automotive, trucking and container shipping industries because they can read distances in excess of 15 feet and can communicate large amounts of information at very high speeds.

Benefits

It offers powerful benefits as part of a comprehensive enterprise mobility strategy.

• Ensure a higher level of patient safety

• Reduce opportunities for counterfeiting, product diversion or substitution along the supply chain

• Rapid identification of product location for improved recall management

• Lower inventory costs with less safety stock and work in process (WIP)

• Minimize inventory loss and write-offs due to concealed shrink and expired product

• Satisfy electronic pedigree requirements

• Simplify processes and cost of regulatory compliance with automation

• Eliminate potential errors from manual-based processes

• Improve productivity across the board

Security

Protection against Tag Clonning :

A second class of defense uses cryptography to prevent tag cloning. Some tags use a form of “rolling code” scheme, wherein the tag identifier information changes after each scan, thus reducing the usefulness of observed responses.

Cryptographically-enabled tags :

More sophisticated devices engage in challenge-response protocols where the tag interacts with the reader. In these protocols, secret tag information is never sent over the insecure communication channel between tag and reader. Rather, the reader issues a challenge to the tag, which responds with a result computed using a cryptographic circuit keyed with some secret value. Such protocols may be based on symmetric or public key cryptography.

Cryptographically-enabled tags typically have dramatically higher cost and power requirements than simpler equivalents, and as a result, deployment of these tags is much more limited. This cost/power limitation has led some manufacturers to implement cryptographic tags using substantially weakened, or proprietary encryption schemes, which do not necessarily resist sophisticated attack.

For example, the Exxon-Mobil Speedpass uses a cryptographically-enabled tag manufactured by Texas Instruments, called the Digital Signature Transponder (DST), which incorporates a weak, proprietary encryption scheme to perform a challenge-response protocol. In 2005, researchers from RSA Labs and Johns Hopkins University reverse engineered the algorithm and were able to clone Speedpass tags.

Types of RFID tags

1. Passive RFID tags

no internal power supply.

electrical current induced in the antenna by the incoming radio frequency signal provides just enough power for the CMOS IC in the tag to power up and transmit a response.

Tags signal by backscattering the carrier signal from the reader. Aerial is designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal.

Rresponse of a passive RFID tag is ID number (GUID) + tag chip can contain nonvolatile EEPROM for storing data.

Read distances ranging from 2 mm – few meters depending on the chosen radio frequency.

Simplicity in design . It is suitable for manufacture with a printing process for the antennae.

Development target are polycarbon semiconductor tags to become entirely printed.
Passive RFID tags do not require batteries, and can be much smaller and have an unlimited life span.

2. Semi-passive RFID tags

similar to passive tags except for the addition of a small battery. This battery allows the tag IC to be constantly powered.

This removes the need for the aerial to be designed to collect power from the incoming signal. Aerials can therefore be optimised for the backscattering signal.

Semi-passive RFID tags are faster in response and therefore stronger in reading ratio compared to passive tags.

3. Active RFID tags or beacons

Have their own internal power source which is used to power any ICs and generate the outgoing signal.

They may have longer range and larger memories than passive tags, as well as the ability to store additional information sent by the transceiver.

To economize power consumption, many beacon concepts operate at fixed intervals. At present, the smallest active tags are about the size of a coin. Many active tags have practical ranges of tens of metres, and a battery life of up to 10 years.

Applications of RFID

Medical Prescriptions 

RFID tags are placed on prescriptions for Visually Impaired Veterans. The Department of Veterans Affairs Outpatient pharmacies are now supplying the tags with label information stored inside that can be read by a battery powered, talking prescription reader. This reader speaks information such as: Drug Name; Instruction; Warnings; etc.

Inventory Management

The data transmitted by the tag may provide identification or location information, or specifics about the product tagged, such as price, color, date of purchase, etc.

Traffic Control

By extending this technology to traffic control and automation, RFID can be used to reduce traffic congestion and avoid accidents efficiently.

Traffic signals need not be static and can be made dynamic by intelligent use of RFID technology depending upon the road traffic conditions.

Animal Collars

Low-frequency RFID tags are commonly used for animal identification. Pets can be implanted with small chips so that they may be returned to their owners if lost. Beer kegs are also tracked with LF RFID.

Libraries / Baggage

High-frequency RFID tags are used in library book or bookstore tracking, pallet tracking, building access control, airline baggage tracking, and apparel item tracking. High-frequency tags are widely used in identification badges, replacing earlier magnetic stripe cards. These badges need only be held within a certain distance of the reader to authenticate the holder. The American Express Blue credit card now includes a high-frequency RFID tag, a feature American Express call express pay.

Truck/ Trailer Tracking in shipping yards

UHF RFID tags are commonly used commercially in pallet and container tracking, and truck and trailer tracking in shipping yards.
Microwave RFID tags are used in long range access control for vehicles.

Remote Data Collection

Sensors such as seismic sensors may be read using RFID transceivers, greatly simplifying remote data collection.
Location sensing of RFID with millimeter accuracy is possible by adding a low cost photo sensor. The real time location sensing supports many complex geometric queries.
Michelin began testing RFID transponders embedded into tires. After a testing period that is expected to last 18 months, the manufacturer will offer RFID enabled tires to car makers. Their primary purpose is tire-tracking in compliance with the United States Transportation, Recall, Enhancement, Accountability and Documentation Act (TREAD Act).

Smart Key/Smart Start

Starting with the 2004, a Smart Key/Smart Start option became available to cars. The key uses an active RFID circuit which allows the car to acknowledge the key’s presence within approximately 3 feet of the sensor. The driver can open the doors and start the car while the key remains in a purse or pocket.