t-Probing Security

Technique

t-Probing security is a formal security notion and adversarial model underlying masking countermeasures against side-channel attacks (SCAs). It bounds the adversary to observing at most t intermediate values (probes) of a masked computation, under the assumption that no set of t shares of any sensitive variable leaks information. The model is foundational for proving the SCA resistance of masked hardware and software implementations, and underpins hardware verification approaches such as leakage contracts.

First seen 6/26/2026

Last seen 6/26/2026

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t-Probing Security

Overview

t-Probing security is a formal security model and proof technique used to argue that a masked implementation of a cryptographic algorithm resists physical side-channel attacks (SCAs) such as power or electromagnetic analysis. The model bounds an adversary's observation capability by a parameter t, representing the maximum number of intermediate variables (probes) the adversary is allowed to observe during a computation. An implementation is said to be t-probing secure if no adversary who observes any set of at most t intermediate values can learn anything about the secret inputs.

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Closing the Gap: Leakage Contracts for Processors with Transitions and Glitches ← uses 88% 2e

They verify software compliance under t-probing and prove end-to-end t-probing security.

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CITATIONS

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[1] t-probing security bounds an adversary to observing at most t intermediate values during a masked computation, and underpins the soundness of masking as an SCA countermeasure. Leakage Contracts for Processors with Transitions and Glitches

[2] A masked computation f : (x, p, r) → (y, q, λ) splits inputs into shared secrets x, public values p, and uniform randomness r, with the t-probing property requiring that any t-subset of λ is simulatable from (p, r) without x. Leakage Contracts for Processors with Transitions and Glitches

[3] Verifying t-probing security (rather than the stronger t-(S)NI notion) is preferred because t-(S)NI implementations trade ease-of-verification for higher randomness requirements. Leakage Contracts for Processors with Transitions and Glitches

[4] A Model Reduction theorem (Bloem et al. [BGG+22]) states that any leakage observable on compliant hardware is also accessible to an attacker observing the contract's λ, so t-probing security of software with respect to a contract implies t-probing security on hardware. Leakage Contracts for Processors with Transitions and Glitches

[5] A precise transition-glitch leakage model makes λ dependent on the gate type and on whether inputs can fluctuate, since naive concatenations of previous and current state values over-approximate and include physically impossible leakage. Leakage Contracts for Processors with Transitions and Glitches

[6] Masking splits every sensitive intermediate variable into at least t+1 shares so that no set of t shares reveals secret information, and t-probing security is used to prove SCA resistance under the assumption that the adversary is bounded by the number of probes or by statistical order. Real-World Snapshots vs. Theory: Questioning the t-Probing Security Model

[7] Laser Logic State Imaging (LLSI) provides a contactless, effectively unlimited number of probes, enabling full AES key extraction from masked hardware via single or multi-snapshot attacks, thereby violating the t-probing security model. Real-World Snapshots vs. Theory: Questioning the t-Probing Security Model

[8] Impedance / scattering-parameter analysis (LeakyOhm) can simultaneously and independently probe individual registers of masked AES hardware and recover the secret key from a single trace, challenging the t-probing security model assumption used in masking. LeakyOhm: Secret Bits Extraction using Impedance Analysis