func()

in otr/smp.go [322:442]
104 lines of code
8 McCabe index (conditional complexity)

func (c *Conversation) processSMP2(mpis []*big.Int) (out tlv, err error) {
	if len(mpis) != 11 {
		err = errors.New("otr: incorrect number of arguments in SMP2 message")
		return
	}
	g2b := mpis[0]
	c2 := mpis[1]
	d2 := mpis[2]
	g3b := mpis[3]
	c3 := mpis[4]
	d3 := mpis[5]
	pb := mpis[6]
	qb := mpis[7]
	cp := mpis[8]
	d5 := mpis[9]
	d6 := mpis[10]
	h := sha256.New()

	r := new(big.Int).Exp(g, d2, p)
	s := new(big.Int).Exp(g2b, c2, p)
	r.Mul(r, s)
	r.Mod(r, p)
	s.SetBytes(hashMPIs(h, 3, r))
	if c2.Cmp(s) != 0 {
		err = errors.New("otr: ZKP c2 failed in SMP2 message")
		return
	}

	r.Exp(g, d3, p)
	s.Exp(g3b, c3, p)
	r.Mul(r, s)
	r.Mod(r, p)
	s.SetBytes(hashMPIs(h, 4, r))
	if c3.Cmp(s) != 0 {
		err = errors.New("otr: ZKP c3 failed in SMP2 message")
		return
	}

	c.smp.g2 = new(big.Int).Exp(g2b, c.smp.a2, p)
	c.smp.g3 = new(big.Int).Exp(g3b, c.smp.a3, p)

	r.Exp(g, d5, p)
	s.Exp(c.smp.g2, d6, p)
	r.Mul(r, s)
	s.Exp(qb, cp, p)
	r.Mul(r, s)
	r.Mod(r, p)

	s.Exp(c.smp.g3, d5, p)
	t := new(big.Int).Exp(pb, cp, p)
	s.Mul(s, t)
	s.Mod(s, p)
	t.SetBytes(hashMPIs(h, 5, s, r))
	if cp.Cmp(t) != 0 {
		err = errors.New("otr: ZKP cP failed in SMP2 message")
		return
	}

	var randBuf [16]byte
	r4 := c.randMPI(randBuf[:])
	r5 := c.randMPI(randBuf[:])
	r6 := c.randMPI(randBuf[:])
	r7 := c.randMPI(randBuf[:])

	pa := new(big.Int).Exp(c.smp.g3, r4, p)
	r.Exp(c.smp.g2, c.smp.secret, p)
	qa := new(big.Int).Exp(g, r4, p)
	qa.Mul(qa, r)
	qa.Mod(qa, p)

	r.Exp(g, r5, p)
	s.Exp(c.smp.g2, r6, p)
	r.Mul(r, s)
	r.Mod(r, p)

	s.Exp(c.smp.g3, r5, p)
	cp.SetBytes(hashMPIs(h, 6, s, r))

	r.Mul(r4, cp)
	d5 = new(big.Int).Sub(r5, r)
	d5.Mod(d5, q)
	if d5.Sign() < 0 {
		d5.Add(d5, q)
	}

	r.Mul(c.smp.secret, cp)
	d6 = new(big.Int).Sub(r6, r)
	d6.Mod(d6, q)
	if d6.Sign() < 0 {
		d6.Add(d6, q)
	}

	r.ModInverse(qb, p)
	qaqb := new(big.Int).Mul(qa, r)
	qaqb.Mod(qaqb, p)

	ra := new(big.Int).Exp(qaqb, c.smp.a3, p)
	r.Exp(qaqb, r7, p)
	s.Exp(g, r7, p)
	cr := new(big.Int).SetBytes(hashMPIs(h, 7, s, r))

	r.Mul(c.smp.a3, cr)
	d7 := new(big.Int).Sub(r7, r)
	d7.Mod(d7, q)
	if d7.Sign() < 0 {
		d7.Add(d7, q)
	}

	c.smp.g3b = g3b
	c.smp.qaqb = qaqb

	r.ModInverse(pb, p)
	c.smp.papb = new(big.Int).Mul(pa, r)
	c.smp.papb.Mod(c.smp.papb, p)
	c.smp.ra = ra

	out.typ = tlvTypeSMP3
	out.data = appendU32(out.data, 8)
	out.data = appendMPIs(out.data, pa, qa, cp, d5, d6, ra, cr, d7)
	return
}