SSCP Question #687: Real Exam Question with Answer & Explanation

Question

When we encrypt or decrypt data there is a basic operation involving ones and zeros where they are compared in a process that looks something like this: 0101 0001 Plain text 0111 0011 Key stream 0010 0010 Output What is this cryptographic operation called?

Options

• AExclusive-OR
• BBit Swapping
• CLogical-NOR
• DDecryption

Explanation

When we encrypt data we are basically taking the plaintext information and applying some key material or keystream and conducting something called an XOR or Exclusive-OR operation. The symbol used for XOR is the following: This is a type of cipher known as a stream cipher. The operation looks like this: 0101 0001 Plain text 0111 0011 Key stream 0010 0010 Output (ciphertext) As you can see, it's not simple addition and the XOR Operation uses something called a truth table that explains why 0+1=1 and 1+1=0. The rules are simples, if both bits are the same the result is zero, if both bits are not the same the The following answers are incorrect: - Bit Swapping: Incorrect. This isn't a known cryptographic operations. - Logical NOR: Sorry, this isn't correct but is where only 0+0=1. All other combinations of 1+1, 1+0 equals 0. More on NOR here. - Decryption: Sorry, this is the opposite of the process of encryption or, the process of applying the keystream to the plaintext to get the resulting encrypted text.

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