Learn in the textbookFundamentals of Encryption and Cipher Methods
DefinitionEncryption (暗号化) uses a key (鍵) and a fixed procedure to turn data that can be read as is (plaintext, 平文) into data that makes no sense to third parties (ciphertext, 暗号文).
ExplanationThe key is the data that decides the result, so the same procedure with a different key yields different ciphertext. Encryption serves confidentiality (機密性), keeping content unreadable to third parties even if it is intercepted or stolen, and it protects stored data as well as communications.
AnalogyIt is like rewriting a letter with a letter-substitution table agreed with the recipient before posting it. Anyone who peeks on the way cannot make sense of it without the table.
Memory hookThe Japanese word 暗号 joins 暗 (dark, unseen) and 号 (sign). Read it as turning text into signs you can see but not read, the forward direction.