For those that want more details on this fun rabbit hole of math, see the theory of Strong Pseudoprimes: https://en.wikipedia.org/wiki/Strong_pseudoprime

Miller-Rabin in considered a simplistic/antiquated primality algorithm in computational number theory. For a much better algorithm see the Baillie–PSW primality test: https://en.wikipedia.org/wiki/Baillie%E2%80%93PSW_primality_... . For an implementation see Math::Prime::Util on CPAN: https://metacpan.org/pod/Math::Prime::Util or one of the many others.

The P in BPSW is for Carl Pomerance mentioned in the academic paper above. According to the wikipedia article "No composite number below 2^64 (approximately 1.845 * 10^19) passes the strong or standard Baillie–PSW test" which means if git-prime used this algorithm and the nonce was below 2^64 (very likely) then it would be provably prime instead of a probabilistic prime and hence have much more "mathematical rigor".

I also agree with other comments here that git-prime would be much cleaner if it put the nonce in git commit header data instead of the message. Something like this was done Long Ago in a "for fun" git patch by Jeff King: https://lore.kernel.org/git/CACBZZX5PqYa0uWiGgs952rk2cy+QRCU...

And he even made a multi-threaded version: https://lore.kernel.org/git/[email protected]...