The IDEA algorithm used in PGP is how many bits long?

The International Data Encryption Algorithm (IDEA) used in Pretty Good Privacy (PGP) is significant for its strong encryption capabilities. It operates with a key size of 128 bits, which provides a robust level of security against brute-force attacks. IDEA was designed to replace the earlier Data Encryption Standard (DES) algorithm, which had a shorter key length of only 56 bits, making it less secure by today’s standards.

The choice of 128 bits allows for a vast number of possible cryptographic keys, specifically 2^128 combinations, which greatly enhances the difficulty for any potential attacker attempting to decode the encrypted data. Additionally, a key length of 128 bits is widely accepted in the field of cryptography as a standard for strong security, ensuring that even with advances in computational power, it remains a secure choice for many applications, including email encryption in PGP.

Other options presented—56 bits, 158 bits, and 168 bits—do not accurately represent the key size of the IDEA algorithm, further solidifying why 128 bits is the correct answer.