Cryptography
- It is a method in which the message is transformed and transported in such a way that it reaches the target user exactly in the same way.
- Encryption and decryption are parts of cryptography.
- It is to convert the form of data in such a way that only the target user can decrypt it.
- Encryption is conversion of plain text into cypher text.
Symmetric encryption
- It uses the same key for coding and decoding both.
- The symmetric encryption uses same key every time. Therefore it can be categorised as a private key. Example user id, password, thumbprint impression, virus scan ,etc.
- User ID ,password in banking transaction are part of public key Cryptography because after the coding it is made available publicly but only a private key can open it.
- If a data is recorded using public key Cryptography then it requires private key to decode it. But if it is coded using private key Cryptography then it requires public key to decode it.
- It uses different key for coding and decoding both therefore it has a different key every time.
- For example OTP acts as a public key when the data is recorded using private key such as user id and password.
- Asymmetric key is also called as public key.
- Private key works faster than public key.
PGP (pretty good privacy)
- It is a type of asymmetric encryption discovered by Phil Zimmermen and it was launched as a free software.
- It is used for email messaging or any other messaging services through internet.
Types of symmetric encryption
There are two types
- Block cipher: it encrypts an entire block of n bit at a time. It appears the form of 32 bit ,64bit, 128 bit etc. In block keeper generally the blocks used are of 64 bit and 128 bit.
- Stream cipher: it is bit by bit encryption such as in WhatsApp and other social media platform.
- It is a unique Identity through which the document can be legally validated.
- The digital signature is a broad term that can be used for many things under internet of things for humans thumbprint impression ,iris scan ,DNA fingerprinting ,etc can work as a digital signature.
- Also the digital signature can be used for a specific programs such as using thumb print impression to unlock phone using voice command to unlock the door , commanding Alexa ,etc.
- It is a part of digital signature only but in e-governance it is based on using biometric impressions such as thumbprint impression and iris scan.
- example:
- Aadhaar enabled payment system :it is a type of digital financial transaction in which Aadhaar card act as used as id and thumb print impression /iris scan acts as password.
- Jeevan pramaan: it is a digital life certificate for government pensioners ,the pensioner do not have to visit their bank personally if they can upload their thumbprint impression and iris scan in Jeevan pramaan app. It will be automatically send to their home Bank branch. There for the pensioners pension will not be denied if they are alive.
- It is to convert 1 large size of file into smaller size of file with or without changing the original data.
- Lower bandwidth
- Lower bandwidth has no power transmission cost
- Lower bandwidth means higher transmission speed
- Lossy compression : file is reduced in size but the original data cannot be obtained.
- Lossless compression: file is reduced in size but the original data can be obtained.
- MPEG (moving picture expert group): they are in form of mpeg 1,2,3 and 4 out of these MPEG3 are used only for audio compression while mpeg1 ,2 and 4 are used for video compression. Mpeg files are a type of lossy compression.
- JPG (joint picture expert group) :it is a type of lossless compression and generally scanned signature are demanded in the form of JPG files.
- PDF (portable document format) :it is a type of lossy compression that can convert the word file into non write table PDF form.
- GIf (graphical interchange format ): it uses lesser number of frames and it can only support 250 colours so as to reduce the file size.
- PNG (portable network graphics): It is based on same principle as that of GIF but it can support millions of colours and it uses a better compression technique.
Barcode
- It consists of thin and thick lines of black colour on a white background.
- It uses high intensity light in red colour wavelength to read the data in barcode.
- The bar code contains information about the product type ,manufacturing date, expiry date, price etc.
- It also has a 13 digit number below it for the same information.
- Black lines observe these lights and white background reflects it.
- Absorbed light is marked as zero and reflected light is marked as one.
- A digital code is created that can be enclosed using the reader.
- It works on the same principle as that of a barcode ,it uses infrared rays to scan it.
- Black lines observe these lights and marked as zero while white background reflects this light to mark it as one.
- A digital code is created that can be decoded using a reader.
- The QR code contain hundred times more information than a barcode. It is also called as quick response code because it does not require to type any account number and IFSC code.
- The QR code requires internet to read the data since data is stored in a remote cloud server while in barcode internet may or may not be required.
- Barcode can be used for specific purposes only while QR code has a wide variety use.
Computer
Basic terms and tools
Boot on:
- This is the most complicated process for computer after the boot on process the software become active and starts copying its data from the disk into the memory. At this time boot strap loader is created. Due to this a link is established between the hardware and the software.
- There are two types of boot on process :
- Warm booting :the computer remembers its old command after the warm booting. Therefore after the restart the computer works faster.
- Cold booting: after the cold booting the RAM loses its data. It works slow.
- It is a compilation of high level language into low level language.
- Machine language called as a low level language while human language are called as high level language.
Primary memory
- It is the inbuilt memory of computer
- It is also called as a volatile memory because it loses its data every time the computer is switched off since RAM stores its data in the form of electric charges.
- RAM is also called as quick memory.
- Types of ram : there are two types-
- Dynamic ram :it loses its data automatically even if the computer remain switched on. Therefore it needs to refresh the data after an interval of time. It is smaller than SRAM.
- SRAM : it does not lose its data automatically till the time the computer remains on therefore it does not need to refresh after a regular interval of time. S RAM is costlier than DRAM. Also it works faster than DRAM.
ROM (Read only memory)
- It is also called as non volatile memory and also a permanent memory .
- ROM is used to store vital data such as operating software.
- ROM stores its data in the form of electrons and holes.
There are three types
PROM (programmable ROM)
- It is possible to write data only once after that it behaves as ROM, since data cannot be deleted after writing once. Example blank CD
- It is possible to write and erase the data as many times as possible but for burning process it uses ultraviolet rays. Example cdR.
- It is possible to write and erase the data as many times as possible but for the burning process it uses electric pulses example pen drive, solid state drive, etc.
Analog signal
Digital signal
It is based on using continuous and variable signal, it varies its data continuously , the speed of analog signal depends upon the slowest particle , therefore these signals are generally slow , these is a single line of communication , therefore , it experience data traffic congestion. Hence it is not able to support high speed internet , eg : voice call using basic telephone
Message is broken into multiple data packet and these data packet can be transmitted through multiple paths since these data packets do not affect each other speed , therefore the digital signal is faster than analog signal , due to multiple path data traffic congestion does not take place therefore it can support high speed internet also.
Analog computers are physicl quantities as input for eg: ammeter , voltmeter , thermometer, etc
Digital computers are those computers that can perform discontinuous functions only. It uses physical quantity as input but output is digital signal , example : simple computer , the digital computer can not perform continuous function such as sin , cos , time based discontinuous , etc.
The digital signal changes direction only magnitude remains constant.
- Function as analog for continuous function and as digital for discontinuous function.
- Capacity up to 1.5 MB
- It consists of a magnetic disk with multiple concentric magnetic layers. Under external magnetic fluid by the floppy drive these magnetic layers become active that can be decoded for message.
- It consists of a plastic disc with a very thin aluminium layer. This layer is highly polished so that it becomes a very good reflector to write data on it high intensity laser light is used that falls on aluminium layer to create and arrangement of pits and plane surfaces.
- Pits are marked as zero and the plane surface is marked as one using low intensity laser light. This digital data can be decoded into the message.
- Its capacity up to 4.7 GB.
- DVD is also based on the same principle as that of CD but it has large number of pits at small distances so that it the data capacity is up to 4.7 GB .
- It is also based on same principle as that of CD and DVD ,its thickness is also same but a blu-ray disc can store data upto 6 to 60 GB due to this we have to use lower wavelength light of blue colour to write and read its data but as the wavelength reduces the frequency increases and such data is categorised as a high definition data.
- These devices can write and erase the data within a click only therefore it does not take any time for writing and erasing hence, it is called as a flash drive.
- Flash drive is general term for multiple devices such as pen drive ,solid state drive ,hard drive, etc.
- These drives along with the USB forms a NAND gate logic circuit.
- The flash drive is made up of semiconductor material with p and n type of doping.
- The digital data of 0 and 1 is marked by n and p type respectively.
- To erase the data simply p and n type combined together.
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