Why Do We Use Keys When Encrypting

KakaoPay Insurance carried out a domain concept-based encryption module refactoring to overcome library compatibility issues and scalability limitations. In this process, they reaffirmed the importance of the Key, which is at the core of encryption design.

Classical ciphers of the past, such as the Caesar cipher, kept the algorithm itself secret, but they were vulnerable to frequency analysis and brute-force attacks. This led to the fundamental premise of modern cryptography, the Kerckhoffs's principle, which states that "the security of a cryptographic system should depend not on the algorithm but on the secrecy of the key."

The widely used key-based encryption methods today are largely divided into two types.

• Symmetric key encryption (Symmetric): AES is a representative example, using the same key for both encryption and decryption. To enhance security, concepts such as the IV (Initialization Vector), which creates a different ciphertext each time, the GCM mode, a chaining method, and Padding, which fills out blocks, are used together.
• Asymmetric key encryption (Asymmetric): RSA is a representative example, using a Public Key for encryption and a Private Key for decryption. As long as the private key is not leaked externally, only the owner can decrypt it, making key management easier than with the symmetric key method.