Advanced Placement (AP) Computer Science

What are 'cribs' in the context of cryptography?

1. Common words and phrases likely to appear in text

2. Techniques used to encrypt messages

3. First letters of each word in a message

4. Patterns in algorithms used for encrypting

The correct answer is: Common words and phrases likely to appear in text

In the context of cryptography, 'cribs' refer to common words and phrases that are likely to appear in the text being analyzed or encoded. These are known elements that cryptanalysts use to assist in deciphering coded messages. By identifying these cribs, which could include frequent words like "the," "and," or common phrases, a cryptanalyst can make educated guesses about portions of the plaintext, thereby facilitating the decryption process. This method is particularly useful when dealing with substitution ciphers, where specific letters or groups of letters are replaced with others. Understanding 'cribs' is crucial in cryptanalysis because they provide a foundational reference point that can lead to the uncovering of broader patterns within encrypted messages. This highlights the importance of language structure and common usage in the realm of cryptography, illustrating how linguistic familiarity can directly assist in breaking codes.