noun
electronic key
Refers to a physical device or card used to unlock doors, start cars, etc., often via radio signal or chip.
このマンションは電子キーで入ります。
You enter this apartment building with an electronic key.
車の電子キーをなくしてしまった。
I lost my car's electronic key.
noun
electronic cipher; digital encryption key
Used in cryptography and IT contexts for a digital key that encrypts or decrypts data. Less common than sense 1 in everyday language.
通信は電子キーで暗号化されている。
The communication is encrypted with an electronic cipher.