OCR J277 Mark Scheme

OCR	GCSE (9-1) Computer Science Mark Scheme J277/01: Unit 1.3 Encryption

Question	Answer	Marks	Guidance
1a	To scramble data so that it cannot be understood if it is intercepted.	1	Examiner's Note: The first option ("Prevent intercepting") is the most common distractor. Encryption does not stop the physical act of interception.
1b	Plaintext	1	Allow: Original Text / Unencrypted Text. Reject: "Normal writing".
1c	Ciphertext	1	Reject: "Coded text" (Too vague).
2a	Look for a padlock icon (in the address bar). Look for 'https://' at the start of the URL.	1	Reject: "Look for the key icon" (Browser dependent/rare). Reject: "The text is scrambled" (Users can't see the packets).
2b	The data contains sensitive financial information (passwords/bank details). (1) If unencrypted, a hacker could read this data and steal money/identity. (1)	2	Context: Must relate to the Bank or Financial nature.
2c	No, they cannot use the data. (1) Because the data is encrypted / scrambled... and the hacker does not possess the key to decrypt it. (1)	2	Examiner's Note: This tests the core concept: Interception != Access. The hacker has the packets (theft successful) but cannot read them (breach failed).
3a	It is used (by the algorithm) to turn plaintext into ciphertext. (1) It is required to turn ciphertext back into plaintext. (1)	2	Analogy: It's the "password" for the algorithm. Accept: "It is used to scramble and unscramble the data."
3b	A longer key has more possible combinations. (1) ...so it would take a hacker much longer to guess/brute-force the correct key. (1)	2	Reject: "It is harder to guess" (Too vague without explaining why - i.e., combinations/time).
4a	Encryption does not stop the data from being physically intercepted/stolen during transmission. (1) It only ensures that the stolen data is unreadable / meaningless to the thief. (1)	2	Crucial Distinction: Encryption protects confidentiality, not availability. The file can still be copied by a hacker.
4b	Any 4 logical steps: Computer A starts with the message as Plaintext. An encryption Algorithm is applied to the data. This converts the data into Ciphertext using a Key. The Ciphertext is transmitted over the network. Computer B uses the (same/private) Key to decrypt the message back into Plaintext.	4	Examiner's Note: Candidates MUST use the bold terms correctly to gain marks. If they describe the process perfectly but call it "Uncoded text" instead of Plaintext, cap at 3 marks. The order must be logical.