Microsoft Technology Licensing, LLC

Ankur Choudhary

Ling Tony Chen

Bradley Joseph Litterell

Felix Stefan Domke

Chong He

Mahima Choudhary

Felix Domke

A TPM is implemented in an SOC for thwarting PIN state replay attacks. Programmable fuses are used as a counter and an on-die RAM stores a blown-fuse count and a TPM state that includes a PIN-failure count and a fuse count. TPM initialization includes incrementing the TPM state PIN-failure count if the blown-fuse count is greater than the TPM state fuse count. Once a PIN is received, if the TPM state PIN-failure count satisfies a PIN failure policy and the PIN is correct, the TPM state PIN-failure count is cleared, and if the PIN is incorrect, a fuse is blown and the blown-fuse count is incremented. If the fuse blow fails, TPM activity is halted. If the fuse blow succeeds, the TPM state PIN-failure count is incremented and the TPM state fuse count is set equal to the blown-fuse count. The TPM state is saved to off-die non-volatile memory.

Fuse based replay protection with conservative fuse usage

An online service may use a computing system to authenticate a remote accessory device by establishing an encrypted communication channel with the remote accessory device, the remote accessory device being connected to a host device. Then, using the encrypted communication channel, obtain a device certificate possessed by the remote accessory device. The online service may then receive a first device token from the remote accessory device and determine whether the first device token exists within a token history associated with the device certificate. Based on the first device token existing within the token history, the online service may then determine that the remote accessory device is an authentic device; generate a second device token for the remote accessory device; store the second device token in the token history associated with the device certificate; and send the second device token to the remote accessory device.

Securing a computing device accessory

A TPM with programmable fuses in an SOC includes an on-die RAM storing a blown-fuse count and a TPM state read from off-die NV memory. During initialization, if the blown-fuse count is greater than a TPM state fuse count, a TPM state PIN-attempt-failure count is incremented, thereby thwarting a replay attack. If a PIN satisfies a PIN failure policy, and if a TPM state previously-passed-PIN indicator is set to true, a fuse is blown and the blown-fuse count incremented depending on the PIN being incorrect, but if the TPM state previously-passed-PIN indicator is set to false, a fuse is blown and the blown-fuse count incremented independent of whether the PIN is correct or incorrect. The TPM state fuse count is set equal to the blown-fuse count. If a counter cleared before processing the PIN remains cleared during the next initialization, a fuse voltage cut is detected and a penalty imposed.

Fuse based replay protection with dynamic fuse usage and countermeasures for fuse voltage cut attacks

A TPM with programmable fuses in an SOC includes an on-die RAM storing a blown-fuse count and a TPM state including a PIN-attempt-failure count and a fuse count, read from off-die NV memory. During initialization, if the blown-fuse count is greater than TPM state fuse count, TPM state PIN-attempt-failure count is incremented, thereby thwarting a replay attack. A PIN is received for access, and if the TPM state PIN-attempt-failure count satisfies a policy, a fuse is blown and the blown-fuse count incremented. If the fuse blow fails, TPM activity is halted. If the fuse blow succeeds and the PIN is correct, the TPM state PIN-attempt-failure count is cleared, but if the PIN is incorrect the TPM state PIN-attempt-failure count is incremented. TPM state fuse count is set equal to the blown-fuse count, and the TPM state is saved to off-die NV memory.

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Redmond, WA, United States of America

Ankur Choudhary