To understand what a Secret Key is, you need to know how 2FA codes are created. We divide 2FA tokens into two types: time-based tokens (TOTP) and event-based tokens (HOTP). Regardless of the type, for the codes to be one-time, individual, and private, they must be calculated based on two variables: a moving factor and a constant factor (also known as a seed). Moving factor causes differentiation of the generated code each time. Most often, it’s time (in the case of TOTP codes) or an event: code refresh counter (in the case of HOTP codes). Constant factor/seed is a variable responsible for assigning the generated codes only to you. And this variable is your Secret Key (also known as the Service Key).
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