Cambridge IT AS Level Summary
This summary does not include pictures
Unit 1
Data: raw numbers, letters, symbols, sounds or images without meaning.
Information: data with context and meaning.
Direct data source: data which has been collected for the purpose for which it
will be used.
Indirect data source: data which was collected for a different purpose
Direct data source Indirect data source
Advantages Data will be relevant, original Immediately availabe, large samples
therefore trusted, up to date are available
and bias data can be
eliminated
Disadvantages Take long time and large The data required may not exist, not
samples are hard to collect too reliable, data can be out of date
and data may be biased
For information to be of high quality it needs to be accurate, relevant to its
purpose, up to date, detailed (not too much or not too little) and complete.
Encryption: scrambling data so it cannot be understood without a decryption
key to make it unreadable if intercepted.
There are 2 types of encryption: symmetric and asymmetric. Symmetric is the
oldest method and requires both the sender and receiver to possess a secret
encryption and decryption key, known as private key. Asymmetric encryption
uses a public key which is available to anybody wanting to send data, and a
private key that is known only to the recipient. The key is the algorithm required
to encrypt and decrypt the data. Asymmetric encryption requires more
processing and takes longer.
To find a public key, digital certificates are required which identify the user or
server and provide the public key, a digital certificate includes: the organisation
, Cambridge IT AS Level Summary
name, the organisation that issued the certificate, the user´s email address,
country and public key.
Asymmetric encryption is used for SSL, the security method. TLS is SSL
improved. Once SSL has established an authenticated session, the client and
server will create symmetric keys for faster secure communication.
SSL: Secure Socket Layer.
TLS: Transport Layer Security.
The hard disk encrypts every single bit of data so in order to Access any file on
the disk the encryption key will be required. This will mean that anyone trying to
Access this information without having the encryption key will not understand
the data.
Normal web pages are searched and transmitted using HTTP (Hypertext
Transfer Protocol), anybody who intercepts web pages will be able to read the
contents of the web page or the data. HTTPS (the secure version) uses SSL or
TLS to encrypt the data. When a browser requests a secure page it will check
the digital certificate to ensure it is trusted. The browser will then use the public
key to encrypt a new symmetric key that is sent to the web server. The browser
and the web page can then communicate using a symmetric encryption (much
faster).
Email uses asymmetric encryption, so the recipients must have the private key
that matches the public key. Encrypting an email will also encrypt any
attachments.
Validation: the process of checking data matches aceptable rules, there are
several types.
Presence check – ensures data is entered
Range check – ensures data is within a certain range (highest and lowest
value)
Type check – ensures data is of a matched type (age is an integer)
, Cambridge IT AS Level Summary
Length check – ensures data is of a certain length (for example a 6
character password)
Lookup check – tests to see if data exists in a list
Format check – ensures data matches a defined format (an email address
contains @)
Check digit – a number or letter is added to the end of an identification
number being input. When the identification number is first created an
algorithm is performed on to it to generate a check digit. When the
identification number is input the same algorithm should match the check
digit, the data is valid when the result of the algorithm matches the check
digit. The data is not valid when the result of the algorithm does not match
the check digit
Consistency check – compares data in one field with data in another field
that already exists within a record
Verification: ensuring data entered matches the original source.
Visual checking – user checks visually that the data entered matches the
original source
Double data entry – input data into the computer twice so the computer
system can compare them
Hash total – calculated by adding together values from an input field for all
the records that need to be input. Before input starts the user manually
adds up the values. The computer will compare the hash total it calculates
automatically with the hash total calculated manually before data entry, if
different there is a mistake
Parity check – used to find errors during data transmission, each byte is
checked individually. With even parity the total number of on bits in a byte
must be an even number the partity bit will be set to on to make the total
on bits even (same process for odd parity)
Checksum – result of a calculation on the contents of a file used to check
wether a file has been copied correctly. Any slight change in a file will
mean that a different checksum is generated, usually represented as
hexadecimals (digits from 0 to 9 and letters from A to F)
This summary does not include pictures
Unit 1
Data: raw numbers, letters, symbols, sounds or images without meaning.
Information: data with context and meaning.
Direct data source: data which has been collected for the purpose for which it
will be used.
Indirect data source: data which was collected for a different purpose
Direct data source Indirect data source
Advantages Data will be relevant, original Immediately availabe, large samples
therefore trusted, up to date are available
and bias data can be
eliminated
Disadvantages Take long time and large The data required may not exist, not
samples are hard to collect too reliable, data can be out of date
and data may be biased
For information to be of high quality it needs to be accurate, relevant to its
purpose, up to date, detailed (not too much or not too little) and complete.
Encryption: scrambling data so it cannot be understood without a decryption
key to make it unreadable if intercepted.
There are 2 types of encryption: symmetric and asymmetric. Symmetric is the
oldest method and requires both the sender and receiver to possess a secret
encryption and decryption key, known as private key. Asymmetric encryption
uses a public key which is available to anybody wanting to send data, and a
private key that is known only to the recipient. The key is the algorithm required
to encrypt and decrypt the data. Asymmetric encryption requires more
processing and takes longer.
To find a public key, digital certificates are required which identify the user or
server and provide the public key, a digital certificate includes: the organisation
, Cambridge IT AS Level Summary
name, the organisation that issued the certificate, the user´s email address,
country and public key.
Asymmetric encryption is used for SSL, the security method. TLS is SSL
improved. Once SSL has established an authenticated session, the client and
server will create symmetric keys for faster secure communication.
SSL: Secure Socket Layer.
TLS: Transport Layer Security.
The hard disk encrypts every single bit of data so in order to Access any file on
the disk the encryption key will be required. This will mean that anyone trying to
Access this information without having the encryption key will not understand
the data.
Normal web pages are searched and transmitted using HTTP (Hypertext
Transfer Protocol), anybody who intercepts web pages will be able to read the
contents of the web page or the data. HTTPS (the secure version) uses SSL or
TLS to encrypt the data. When a browser requests a secure page it will check
the digital certificate to ensure it is trusted. The browser will then use the public
key to encrypt a new symmetric key that is sent to the web server. The browser
and the web page can then communicate using a symmetric encryption (much
faster).
Email uses asymmetric encryption, so the recipients must have the private key
that matches the public key. Encrypting an email will also encrypt any
attachments.
Validation: the process of checking data matches aceptable rules, there are
several types.
Presence check – ensures data is entered
Range check – ensures data is within a certain range (highest and lowest
value)
Type check – ensures data is of a matched type (age is an integer)
, Cambridge IT AS Level Summary
Length check – ensures data is of a certain length (for example a 6
character password)
Lookup check – tests to see if data exists in a list
Format check – ensures data matches a defined format (an email address
contains @)
Check digit – a number or letter is added to the end of an identification
number being input. When the identification number is first created an
algorithm is performed on to it to generate a check digit. When the
identification number is input the same algorithm should match the check
digit, the data is valid when the result of the algorithm matches the check
digit. The data is not valid when the result of the algorithm does not match
the check digit
Consistency check – compares data in one field with data in another field
that already exists within a record
Verification: ensuring data entered matches the original source.
Visual checking – user checks visually that the data entered matches the
original source
Double data entry – input data into the computer twice so the computer
system can compare them
Hash total – calculated by adding together values from an input field for all
the records that need to be input. Before input starts the user manually
adds up the values. The computer will compare the hash total it calculates
automatically with the hash total calculated manually before data entry, if
different there is a mistake
Parity check – used to find errors during data transmission, each byte is
checked individually. With even parity the total number of on bits in a byte
must be an even number the partity bit will be set to on to make the total
on bits even (same process for odd parity)
Checksum – result of a calculation on the contents of a file used to check
wether a file has been copied correctly. Any slight change in a file will
mean that a different checksum is generated, usually represented as
hexadecimals (digits from 0 to 9 and letters from A to F)
