From afc801186f2591555eb43c0138ac1951da02cea4 Mon Sep 17 00:00:00 2001
From: siddharth <s@ricketyspace.net>
Date: Sat, 9 Apr 2022 20:26:52 -0400
Subject: lib: add NewSRPClientSession

---
 lib/srp.go      | 30 ++++++++++++++++++++++++++++++
 lib/srp_test.go | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/lib/srp.go b/lib/srp.go
index 20208a6..491565c 100644
--- a/lib/srp.go
+++ b/lib/srp.go
@@ -78,6 +78,8 @@ type SRPClientSession struct {
 	// Multipier parameter. Client and server agree upon the value
 	// of N.
 	k *big.Int
+	// Hashing object for H() function.
+	h Sha256
 	// User's email address
 	ident string
 	// Scrambling parameter.
@@ -131,3 +133,31 @@ func NewSRPUser(n, g, k, ident, pass string) (*SRPUser, error) {
 
 	return user, nil
 }
+
+func NewSRPClientSession(n, g, k, ident string) (*SRPClientSession, error) {
+	var ok bool
+
+	session := new(SRPClientSession)
+	session.n, ok = new(big.Int).SetString(StripSpaceChars(n), 16)
+	if !ok {
+		return nil, CPError{"n is invalid"}
+	}
+	session.g, ok = new(big.Int).SetString(StripSpaceChars(g), 16)
+	if !ok {
+		return nil, CPError{"g is invalid"}
+	}
+	session.k, ok = new(big.Int).SetString(StripSpaceChars(k), 16)
+	if !ok {
+		return nil, CPError{"k is invalid"}
+	}
+	session.ident = ident
+
+	// Initialize hashing object.
+	session.h = Sha256{}
+	session.h.Init([]uint32{})
+
+	// Generate secret ephemeral value.
+	session.a = big.NewInt(RandomInt(1, 10000000))
+
+	return session, nil
+}
diff --git a/lib/srp_test.go b/lib/srp_test.go
index d7e3b0d..a31e658 100644
--- a/lib/srp_test.go
+++ b/lib/srp_test.go
@@ -67,3 +67,52 @@ func TestNewSRPUser(t *testing.T) {
 		return
 	}
 }
+
+func TestNewSRPClientSession(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
+	}
+
+	// Check n.
+	bigN, _ := new(big.Int).SetString(StripSpaceChars(n), 16)
+	if session.n.Cmp(bigN) != 0 {
+		t.Error("Error: n not set correctly\n")
+		return
+	}
+	// Check g.
+	bigG, _ := new(big.Int).SetString(StripSpaceChars(g), 16)
+	if session.g.Cmp(bigG) != 0 {
+		t.Error("Error: g not set correctly\n")
+		return
+	}
+	// Check k.
+	bigK, _ := new(big.Int).SetString(StripSpaceChars(k), 16)
+	if session.k.Cmp(bigK) != 0 {
+		t.Error("Error: k not set correctly\n")
+		return
+	}
+	// Check ident.
+	if session.ident != ident {
+		t.Error("Error: user not set correctly\n")
+		return
+	}
+	// Check a.
+	if session.a.Cmp(big.NewInt(1)) < 0 {
+		t.Error("Error: a not set correctly\n")
+		return
+	}
+}
-- 
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