SHA-256 Cryptanalysis and Signal Processing Demonstrator

This tool explores SHA-256’s security through naive collision attempts, zero-fields, fixed points, and a signal processing analogy where collisions are aliasing events.

Core Engine Verification

Click to verify the SHA-256 implementation against the standard "abc" test vector.

Free-Start Collision and Analysis

Understanding SHA-256 as a Signal Processor

SHA-256’s compression function (H = IV + Permutation(IV, M)) can be viewed as a signal processing system:

Signal: Message M is a unique bit pattern.
High-Frequency Diffusion: Rotations (ROTR) spread bits rapidly, like high-frequency modulation.
Non-Linear Sampling: Modular addition, Ch, Maj mix the state chaotically each round.
Aliasing (Collision): Two distinct signals (M1, M2) produce the same hash when sampled.

Naive Collision Attempt: Fails due to the avalanche effect, where small input changes cause large output differences, resisting aliasing.

Sliding Zero-Field: Forces a zero state for a range of rounds, like a “flat signal,” simplifying differential paths but requiring complex connections.

Fixed Points: Values stable under rotations (e.g., 0x00000000 for ROTR(X, 7)) act as “pure tones” but are disrupted by non-linear operations.

Key Lesson: SHA-256’s non-linear sampling and high diffusion make aliasing (collisions) infeasible, even with cryptanalytic gadgets.