Encryption | Computer for GCSE/IGCSE - Year 11 PDF Download

Encryption

• Various dangers pose risks to the security of systems and networks, including:
  • Malware: Software designed to damage or infiltrate computer systems.
  • Viruses: Programs that replicate themselves and spread to other computers.
  • Spyware: Software that collects information about a person or organization without their knowledge.
  • Hackers: Individuals attempting unauthorized access to computers and networks through various means.
  • Denial of service attacks: Attempts to make a machine or network resource unavailable to its intended users.
  • Social engineering: Manipulating people into performing actions or divulging confidential information.
  • SQL injection: Exploiting vulnerabilities in a website's software to access its database.

Understanding Hackers

• Hackers are individuals who attempt to gain unauthorized access to computers, networks, and data by creating malicious programs.
• They identify system vulnerabilities and exploit them to gain entry.
• Hackers may have various motives, including financial gain, seeking challenges, or protesting against something.
• Some hackers target data for theft or to disrupt access, such as through ransomware attacks.
• They might utilize packet sniffers to intercept and analyze data transmitted over networks.
• Encrypting data can be crucial to safeguard against hackers looking to misuse personal information.

Understanding Encryption

• Encryption is the process of converting data into a format that is unintelligible through the use of algorithms.
  • For instance, a simple phrase like "Computer Science" can be transformed into a seemingly random string such as "YekLKEZizFuFjHNCjHj3Md7qyTiGxLNNwPVFZtJU74I=".
• Once encrypted, data can be decrypted, reverting the encoded information back to its original form.
• While encryption doesn't guarantee immunity from hackers, it significantly complicates data comprehension without the corresponding decryption tools.

Types of Encryption

• Symmetric Encryption: In this method, the same key is used for both encryption and decryption processes, ensuring secure communication between two parties.
• Asymmetric Encryption: Also known as public-key encryption, this technique involves a pair of keys - public and private - to encrypt and decrypt data, enhancing security in digital transactions.
• Encryption is a method that doesn't prevent data theft but makes it challenging for hackers to interpret the data.

Symmetric and Asymmetric Encryption

• Encryption relies on the utilization of a key. A key, a binary string of specific length, is employed by encryption algorithms to encode plaintext information and decode ciphertext.
  • Plaintext denotes data before encryption, while Ciphertext refers to data after encryption.
• Keys, akin to passwords, come in various sizes, serving as safeguards for information. An error in the key renders data decryption impossible. Modern strong keys can exceed 1000 bits in length.

Symmetric Encryption

• Symmetric encryption involves both parties possessing an identical secret key, enabling them to encrypt or decrypt data.
• The key distribution problem arises when a hacker gains access to the key, granting them the ability to decrypt intercepted information.
• Techniques exist for securely transmitting the secret key without electronic means:
  • Both parties can verbally exchange the key in person.
  • Standard postal mail can be used to share the key, a practice adopted by certain businesses and banks for identity verification.
  • Alternatively, an algorithm can derive the key through the exchange of secret non-key information. An example is provided below.

Symmetric Encryption Walkthrough

• Initial Number Selection: Both parties, A and B, select a number each, for instance, A = 3 and B = 2.
• Equation Setup: Each party inputs their chosen numbers into the following equations: 7^A MOD 11 or 7^B MOD 11.
  For example, 7^3 MOD 11 = 2 and 7^2 MOD 11 = 5.
• Answer Exchange: The parties exchange their answers. A receives 5, and B receives 2.
• Iteration: The received answers replace the initial 7, and the calculations are repeated.
  Subsequently, new numbers are generated and entered into the equations.
  For instance, 5^3 MOD 11 = 4, and 2^2 MOD 11 = 4.
• Key Generation: The final matching answer serves as the encryption and decryption key for both parties.

Application of Key in Encryption and Decryption

• Both parties, labeled as A and B, select a number each. For instance, let's say A = 3 and B = 2.
• They input their respective numbers into the following formulas: 7 to the power of A, MOD 11, or 7 to the power of B, MOD 11. The ^ symbol denotes "to the power of." For example, when A = 3, 7^3 MOD 11 equals 2, and when B = 2, 7^2 MOD 11 equals 5.
• Next, A and B exchange their computed results. A now possesses 5, while B has 2. These outcomes replace the initial 7, and the calculations are repeated.
• Subsequently, they substitute their new numbers into the equations: 5 to the power of 3, MOD 11, or 2 to the power of 2, MOD 11. This yields 5^3 MOD 11 = 4 and 2^2 MOD 11 = 4.
• The final answer, which should match for both parties, serves as the encryption and decryption key value.

After generating the key, it's used in the algorithm to encrypt the plaintext, resulting in ciphertext sent to the receiver.
The receiver receives the ciphertext along with the key, utilizing the encryption algorithm to decrypt it and retrieve the original plaintext.

Asymmetric Encryption

• Asymmetric encryption, also known as public key encryption, involves the use of two keys:
  • Public key: This key is widely known and accessible to everyone.
  • Private key: This key is kept confidential and known only to the intended recipient.
• Both the public and private keys are essential for encrypting and decrypting information securely.
• The process of asymmetric encryption unfolds as follows:
  • Person A leverages a public key to encode their message.
  • The encoded message is then transmitted over a network or the internet.
  • Person B decodes the message using their unique private key.
• Notably, asymmetric encryption ensures that a single private key is capable of decrypting the message, enhancing security by keeping the key private and not transmitting it over the internet.
• The keys used in asymmetric encryption can be quite large, such as over 1000 bits. The vast number of possible combinations makes it extremely challenging for a hacker to determine the correct key. For instance, a key containing only 100 bits would yield an immense number of combinations, totaling over 1.2 undecillion.

How Encryption Keys are Generated?

• Encryption keys can be produced manually, randomly, or through an algorithm.
• Robust encryption keys are crafted using a hashing algorithm.
• A hashing algorithm is a mathematical process that transforms an input into an output in a manner that cannot be reversed.
• To create encryption keys, a message or key is input into the hashing algorithm, generating a string of characters typically displayed in hexadecimal format.
• SHA-2 stands as a prime example of a hashing algorithm, generating hashed keys of lengths such as 244, 256, 384, or 512 bits. For instance, applying the text "Computer Science" through the SHA-2 algorithm yields a 512-bit hexadecimal key like "B6e175f5fc647b1a9ce17019594ce55b58e8fd03e3c584ee384121c8b4c7753d".
• The resulting hashed encryption key can be transmitted symmetrically or kept confidential within an asymmetric private key.
• For decryption, both the sender and receiver must possess a copy of the key, whether they employ symmetric or asymmetric encryption methods.

Why are Hashed Encryption Keys Used?

• Symmetric vs. Asymmetric Encryption:In symmetric encryption, the key must be sent with the message to the receiver. If a hacker intercepts the key, they can read the message. On the other hand, in asymmetric encryption, the public key is available to everyone and would not be useful to a hacker. The hacker must guess the private key in order to read the message.
• Many-to-One Hashing Algorithms:Hashing algorithms are many-to-one, meaning that many input values, messages, or keys can produce the same hash key output. This property implies that a hashed encryption key requires the hacker to first unhash the key before it becomes useful.
• Non-Reversible Nature of Hashing:As hashing algorithms are non-reversible, reversing the process is exceedingly difficult. For instance, with SHA-2, a hacker attempting to find the symmetric or asymmetric private key must calculate over 1.3x10^154 combinations, which is practically impossible given current computing power.