From cdb98133c282ee2fb51430001ad0bd8ee8328f7e Mon Sep 17 00:00:00 2001
From: siddharth ravikumar <s@ricketyspace.net>
Date: Sun, 12 Jun 2022 16:48:58 -0400
Subject: lib: add handling for simplified srp

---
 lib/srp.go | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

(limited to 'lib/srp.go')

diff --git a/lib/srp.go b/lib/srp.go
index aa3a956..892ba8c 100644
--- a/lib/srp.go
+++ b/lib/srp.go
@@ -173,6 +173,21 @@ func (u *SRPUser) EphemeralKeyPub() (*big.Int, error) {
 	return pub, nil
 }
 
+func (u *SRPUser) EphemeralKeyPubSimple() (*big.Int, error) {
+	if u.g == nil || u.g.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"g is not initialized"}
+	}
+	if u.b == nil || u.b.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"b is not initialized"}
+	}
+
+	// pub is 'B'
+	pub := new(big.Int)
+	pub.Exp(u.g, u.b, u.n)
+
+	return pub, nil
+}
+
 func (u *SRPUser) SetScramblingParam(a *big.Int) error {
 	b, err := u.EphemeralKeyPub()
 	if err != nil {
@@ -202,6 +217,22 @@ func (u *SRPUser) SetScramblingParam(a *big.Int) error {
 	return nil
 }
 
+func (u *SRPUser) SetScramblingParamSimple() error {
+	// random 128-bits
+	r, err := RandomBytes(16)
+	if err != nil {
+		return err
+	}
+
+	// Set scrambling paramter u
+	u.u = new(big.Int)
+	u.u.SetBytes(r)
+	if u.u.Cmp(big.NewInt(0)) != 1 {
+		return CPError{"u is invalid"}
+	}
+	return nil
+}
+
 func (u *SRPUser) ComputeSessionKey(a *big.Int) error {
 	// v^u
 	vu := new(big.Int)
@@ -346,6 +377,20 @@ func (s *SRPClientSession) SetScramblingParam(b *big.Int) error {
 	return nil
 }
 
+func (s *SRPClientSession) SetScramblingParamSimple(u []byte) error {
+	if len(u) < 16 {
+		return CPError{"server u is invalid"}
+	}
+
+	// Set scrambling paramter u
+	s.u = new(big.Int)
+	s.u.SetBytes(u)
+	if s.u.Cmp(big.NewInt(0)) != 1 {
+		return CPError{"u is invalid"}
+	}
+	return nil
+}
+
 func (s *SRPClientSession) ComputeSessionKey(salt []byte,
 	pass string, b *big.Int) error {
 	if len(salt) < 1 {
@@ -396,6 +441,44 @@ func (s *SRPClientSession) ComputeSessionKey(salt []byte,
 	return nil
 }
 
+func (s *SRPClientSession) ComputeSessionKeySimple(salt []byte,
+	pass string, b *big.Int) error {
+	if len(salt) < 1 {
+		return CPError{"salt invalid"}
+	}
+
+	// salt+pass
+	sp := make([]byte, 0)
+	copy(sp, salt)
+	sp = append(sp, StrToBytes(pass)...)
+
+	// x = H(salt+pass)
+	x := new(big.Int)
+	s.h.Message(sp)
+	x.SetBytes(s.h.Hash())
+
+	// u * x
+	ux := new(big.Int)
+	ux.Mul(s.u, x)
+
+	// a + u*x
+	aux := new(big.Int)
+	aux.Add(s.a, ux)
+
+	// S = (B) ^ (a + u*x)
+	sec := new(big.Int)
+	sec.Exp(b, aux, s.n)
+	sb := sec.Bytes()
+
+	// K = H(S)
+	m := make([]byte, 0)
+	m = append(m, sb...)
+	s.h.Message(m)
+	s.sk = s.h.Hash()
+
+	return nil
+}
+
 func (s *SRPClientSession) SetSessionKey(key []byte) {
 	s.sk = key
 }
-- 
cgit v1.2.3