Compare two RSA keys in Go

samersa.go

package main

import (
	"crypto/rsa"
	"errors"
	"fmt"
	"math/big"
)

const confidence = 100

var one = new(big.Int).SetInt64(1)

var (
	ErrPrimality = errors.New("primality test failed")
	ErrModulus   = errors.New("p*q != N")
	ErrInverse   = errors.New("bad inversion")
)

func fromBase10(s string) *big.Int {
	b, ok := new(big.Int).SetString(s, 10)
	if !ok {
		panic(ok)
	}
	return b
}

func cmpPrivateKeys(pkA, pkB *rsa.PrivateKey) error {
	var (
		N    = pkA.PublicKey.N
		p, q = pkB.Primes[0], pkB.Primes[1]

		E, D = pkA.D, big.NewInt(int64(pkB.PublicKey.E))
	)

	if !p.ProbablyPrime(confidence) || !q.ProbablyPrime(confidence) {
		return ErrPrimality
	}

	if !sameN(p, q, N) {
		return ErrModulus
	}

	ϕ := new(big.Int).Mul(
		new(big.Int).Sub(p, one),
		new(big.Int).Sub(q, one),
	)
	if new(big.Int).ModInverse(E, ϕ).Cmp(D) != 0 {
		return ErrInverse
	}
	return nil
}

func sameN(p, q, N *big.Int) bool {
	return new(big.Int).Mul(p, q).Cmp(N) == 0
}

func sameRSA(pk0, pk1 *rsa.PrivateKey) bool {
	if len(pk0.Primes) != len(pk1.Primes) {
		return false
	}
	err := cmpPrivateKeys(pk0, pk1)
	return err == nil
}

func main() {
	pk0 := &rsa.PrivateKey{
		PublicKey: rsa.PublicKey{
			N: fromBase10("143"),
			E: 7,
		},
		D: fromBase10("103"),
		Primes: []*big.Int{
			fromBase10("11"),
			fromBase10("13"),
		},
	}

	pk1 := &rsa.PrivateKey{
		PublicKey: rsa.PublicKey{
			E: 7,
			N: fromBase10("143"),
		},
		D: fromBase10("103"),
		Primes: []*big.Int{
			fromBase10("13"),
			fromBase10("11"),
		},
	}
	fmt.Println(sameRSA(pk0, pk1))
}