dh.go

package otr4

import "math/big"

var (
	p         *big.Int // prime field, assigned in RFC3526 with id 15
	pMinusTwo *big.Int // for the interval [2, p−2]
	q         *big.Int // prime order
	g3        *big.Int // group generator for Diffie-Hellman
)

func init() {
	p, _ = new(big.Int).SetString(
		"FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1"+
			"29024E088A67CC74020BBEA63B139B22514A08798E3404DD"+
			"EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245"+
			"E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED"+
			"EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D"+
			"C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F"+
			"83655D23DCA3AD961C62F356208552BB9ED529077096966D"+
			"670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B"+
			"E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9"+
			"DE2BCBF6955817183995497CEA956AE515D2261898FA0510"+
			"15728E5A8AAAC42DAD33170D04507A33A85521ABDF1CBA64"+
			"ECFB850458DBEF0A8AEA71575D060C7DB3970F85A6E1E4C7"+
			"ABF5AE8CDB0933D71E8C94E04A25619DCEE3D2261AD2EE6B"+
			"F12FFA06D98A0864D87602733EC86A64521F2B18177B200C"+
			"BBE117577A615D6C770988C0BAD946E208E24FA074E5AB31"+
			"43DB5BFCE0FD108E4B82D120A93AD2CAFFFFFFFFFFFFFFFF", 16)

	q, _ = new(big.Int).SetString(
		"7FFFFFFFFFFFFFFFE487ED5110B4611A62633145C06E0E68"+
			"948127044533E63A0105DF531D89CD9128A5043CC71A026E"+
			"F7CA8CD9E69D218D98158536F92F8A1BA7F09AB6B6A8E122"+
			"F242DABB312F3F637A262174D31BF6B585FFAE5B7A035BF6"+
			"F71C35FDAD44CFD2D74F9208BE258FF324943328F6722D9E"+
			"E1003E5C50B1DF82CC6D241B0E2AE9CD348B1FD47E9267AF"+
			"C1B2AE91EE51D6CB0E3179AB1042A95DCF6A9483B84B4B36"+
			"B3861AA7255E4C0278BA3604650C10BE19482F23171B671D"+
			"F1CF3B960C074301CD93C1D17603D147DAE2AEF837A62964"+
			"EF15E5FB4AAC0B8C1CCAA4BE754AB5728AE9130C4C7D0288"+
			"0AB9472D45556216D6998B8682283D19D42A90D5EF8E5D32"+
			"767DC2822C6DF785457538ABAE83063ED9CB87C2D370F263"+
			"D5FAD7466D8499EB8F464A702512B0CEE771E9130D697735"+
			"F897FD036CC504326C3B01399F643532290F958C0BBD9006"+
			"5DF08BABBD30AEB63B84C4605D6CA371047127D03A72D598"+
			"A1EDADFE707E884725C16890549D69657FFFFFFFFFFFFFFF", 16)

	// for checking
	pMinusTwo = sub(p, big.NewInt(2))
	g3 = big.NewInt(2)
}

func isGroupElement(n *big.Int) bool {
	return greatOrEqual(n, g3) && lessOrEqual(n, pMinusTwo)
}