Modular arithmetic, primality, CRT, curve parameters, RSA sizing, encodings, entropy and check digits.
payments ON MAINNET (real money) · 10 live endpoints
| Endpoint | Price | What it answers |
|---|---|---|
GET /check-digits | $0.02 | Generate or validate Luhn and ISO 7064 mod 97-10 (IBAN style) check digits from the string you supply. |
GET /crt | $0.02 | Solve x = a1 (mod m1), x = a2 (mod m2), ... with the Chinese remainder theorem, coprime or not. |
GET /ec-params | $0.02 | secp256k1, P-256 and P-384 public parameters (p, n, G) from SEC 2, with an on-curve check of a public point. |
GET /encoding | $0.02 | Convert public bytes between hex, base64 and base64url (RFC 4648) with strict decoding and expected-length check. |
GET /entropy | $0.02 | Shannon entropy in bits per symbol from a frequency table, plus min-entropy, collision entropy and efficiency. |
GET /gcd-extended | $0.02 | gcd, lcm and extended-Euclid Bezout coefficients of two integers, plus gcd/lcm of up to 20 more. |
GET /mod-inverse | $0.02 | Modular multiplicative inverse of a mod m, or the gcd that proves none exists. |
GET /mod-pow | $0.02 | Modular exponentiation base^exp mod m for big integers, decimal or 0x hex, up to 4096 bits. |
GET /prime | $0.02 | Primality test (deterministic Miller-Rabin below 2^64) plus the next and previous prime, with BigInt. |
GET /rsa-arith | $0.02 | RSA public key arithmetic: modulus bits, exponent validity, NIST strength; or a labelled toy RSA with tiny primes. |
GET /catalog returns this list as JSON. Activity hub · uptime.
Educational arithmetic on PUBLIC values computed locally, provided as is. Never send private keys, seeds, mnemonics, passphrases or secret exponents to this or any service: obviously key-shaped inputs are refused. The code is not constant-time and is not a cryptographic library. Toy RSA is an educational illustration with tiny primes and must never protect anything. Not security advice. Every paid response carries a disclaimer field.