From ac3632e554c576c4d7e24bca17d3f23abf664883 Mon Sep 17 00:00:00 2001
From: siddharth <s@ricketyspace.net>
Date: Sun, 10 Apr 2022 11:07:52 -0400
Subject: lib: add srp ephemeral functions

---
 lib/srp.go      | 51 ++++++++++++++++++++++++++++++++++++++++++++
 lib/srp_test.go | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)

diff --git a/lib/srp.go b/lib/srp.go
index 491565c..05b61ab 100644
--- a/lib/srp.go
+++ b/lib/srp.go
@@ -134,6 +134,42 @@ func NewSRPUser(n, g, k, ident, pass string) (*SRPUser, error) {
 	return user, nil
 }
 
+func (u *SRPUser) EphemeralKeyGen() {
+	for {
+		u.b = big.NewInt(RandomInt(1, 10000000))
+		if u.b.Cmp(big.NewInt(0)) == 1 {
+			break
+		}
+	}
+}
+
+func (u *SRPUser) EphemeralKeyPub() (*big.Int, error) {
+	if u.k == nil || u.k.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"k is not initialized"}
+	}
+	if u.v == nil || u.v.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"v is not initialized"}
+	}
+	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"}
+	}
+
+	kv := new(big.Int)
+	kv.Mul(u.k, u.v)
+
+	gb := new(big.Int)
+	gb.Exp(u.g, u.b, u.n)
+
+	// pub is 'B'
+	pub := new(big.Int)
+	pub.Add(kv, gb)
+
+	return pub, nil
+}
+
 func NewSRPClientSession(n, g, k, ident string) (*SRPClientSession, error) {
 	var ok bool
 
@@ -161,3 +197,18 @@ func NewSRPClientSession(n, g, k, ident string) (*SRPClientSession, error) {
 
 	return session, nil
 }
+
+func (s *SRPClientSession) EphemeralKeyPub() (*big.Int, error) {
+	if s.g == nil || s.g.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"g is not initialized"}
+	}
+	if s.a == nil || s.a.Cmp(big.NewInt(0)) != 1 {
+		return nil, CPError{"a is not initialized"}
+	}
+
+	// pub is 'A'
+	pub := new(big.Int)
+	pub.Exp(s.g, s.a, s.n)
+
+	return pub, nil
+}
diff --git a/lib/srp_test.go b/lib/srp_test.go
index a31e658..3e3c8d6 100644
--- a/lib/srp_test.go
+++ b/lib/srp_test.go
@@ -68,6 +68,42 @@ func TestNewSRPUser(t *testing.T) {
 	}
 }
 
+func TestSRPUserEphemeralKey(t *testing.T) {
+	n := StripSpaceChars(
+		`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
+                 e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
+                 3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
+                 6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
+                 24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
+                 c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
+                 bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
+                 fffffffffffff`)
+	g := "2"
+	k := "3"
+	ident := "s@ricketyspace.net"
+	pass := "d59d6c93af0f37f272d924979"
+	user, err := NewSRPUser(n, g, k, ident, pass)
+	if err != nil {
+		t.Errorf("Error: %v\n", err)
+		return
+	}
+
+	user.EphemeralKeyGen()
+	if user.b.Cmp(big.NewInt(0)) != 1 {
+		t.Errorf("Error: b is <= 0")
+		return
+	}
+	pub, err := user.EphemeralKeyPub()
+	if err != nil {
+		t.Errorf("Error: %v\n", err)
+		return
+	}
+	if pub.Cmp(big.NewInt(0)) != 1 {
+		t.Errorf("Error: pub is <= 0")
+		return
+	}
+}
+
 func TestNewSRPClientSession(t *testing.T) {
 	n := StripSpaceChars(
 		`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
@@ -116,3 +152,33 @@ func TestNewSRPClientSession(t *testing.T) {
 		return
 	}
 }
+
+func TestSRPClientSessionEphemeralKeyPub(t *testing.T) {
+	n := StripSpaceChars(
+		`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
+                 e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
+                 3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
+                 6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
+                 24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
+                 c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
+                 bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
+                 fffffffffffff`)
+	g := "2"
+	k := "3"
+	ident := "s@ricketyspace.net"
+	session, err := NewSRPClientSession(n, g, k, ident)
+	if err != nil {
+		t.Errorf("Error: %v\n", err)
+		return
+	}
+
+	pub, err := session.EphemeralKeyPub()
+	if err != nil {
+		t.Errorf("Error: %v\n", err)
+		return
+	}
+	if pub.Cmp(big.NewInt(0)) != 1 {
+		t.Errorf("Error: pub is <= 0")
+		return
+	}
+}
-- 
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