STEM
PrimeDojo
Multiply two primes: easy. Un-multiply their product: nearly impossible. That one gap is what RSA encryption relies on. PrimeDojo walks you from clock arithmetic to a working RSA key you build, encrypt with, decrypt with — and then BREAK by factoring, all by hand and all on your device. Predict each step, then watch the maths. Ages 15–18.
▶ Play it nowBuilt for sittings of about 25 minutes on the screen. That is our design budget, not a measurement.
#2b8a8a Characters who teach
Meet the cast
PrimeDojo is for ages 15–18 — no illustrated cast; the 'characters' are the pieces of an RSA key whose relationship IS the security. The modulus n = p·q is public, and its two prime factors are the whole secret. Euler's φ(n) = (p−1)(q−1) is the size of the clock the keys live on — computable only if you know p and q. The public exponent e locks a message (raise it to e); the private exponent d = e⁻¹ mod φ unlocks it (raise it to d). An attacker who could factor n would rebuild φ and then your d — so RSA is safe exactly when n is too big to factor. Every value is exact integer arithmetic computed on-device (mod, modpow, modinv, factor).
The modulus n = p·q
The public modulus — the product of two secret primes; its two prime factors are the entire secret of the key
Euler's φ(n)
The size of the clock the keys live on, (p−1)(q−1); computable only if you know p and q — which is why factoring n breaks everything
The public exponent e
Any number coprime to φ; encrypting is raising the message to the power e on the clock of size n — anyone can do it
The private exponent d
The modular inverse of e (d = e⁻¹ mod φ); it undoes encryption, and an attacker can find it only by first factoring n
What's inside
Learning goal
Multiply two primes: easy. Un-multiply their product: nearly impossible. That one gap is what RSA encryption relies on. PrimeDojo walks you from clock arithmetic to a working RSA key you build, encrypt with, decrypt with — and then BREAK by factoring, all by hand and all on your device. Predict each step, then watch the maths. Ages 15–18.
How PrimeDojo handles your kid's data
- ✅ All progress, settings, and AI-generated content stays on the device
- ✅ No analytics, no tracking, no third-party SDKs
- ✅ Free — no ads, no in-app purchases
- ✅ No personal information collected from children — in line with COPPA (updated by the 2026 FTC amendments)
- ✅ No chat with strangers — play-together rooms use a short code and preset emotes, never typed messages