A one time password (OTP) associated with a client device, and a padding rule, of a plurality of possible padding rules, associated with the client device may be determined. A padded OTP that includes the OTP and additional data may be formed based on the padding rule. The padding rule may be associated with at least one of a position of the OTP within the padded OTP, a characteristic of the additional data, or a characteristic of the padded OTP. The padded OTP may be provided to the client device. A selection of a portion of the padded OTP may be received from the client device, and the client device may be authenticated when the selected portion of the padded OTP corresponds to the OTP. If the selected portion of the padded OTP does not correspond to the OTP, other actions may be performed based on the selected portion.