Lambda-Shield v4: A Collatz-Trajectory Stream Cipher with SipHash-1-2 Mixing — 162/162 NIST SP 800-22 Tests Passed

We present Lambda-Shield v4, a lightweight stream cipher designed for resource-constrained 
environments (IoT, embedded MCUs). The construction uses the Collatz map as a non-linear 
state driver, mixed through SipHash-1-2 ARX rounds to produce a statistically clean 
keystream. All operations are wrapping integer add, XOR, and rotate — no S-boxes, no 
lookup tables, suitable for ARM Cortex-M0 with no dedicated crypto hardware.

The paper documents the full development history from v1 (62.5% bit bias, broken) through 
v4 (statistically validated), including bias discovery, autocorrelation analysis, and 
remediation. The final construction passes all 162 applicable NIST SP 800-22 tests using 
the official STS v2.1.2 binary with zero failures.

Implementation available at: https://crates.io/crates/lambda-shield (MIT)
Source: https://github.com/0x-auth/lambda-shield