lib: implement diffie-hellman

1 files changed, 41 insertions, 0 deletions

diff --git a/lib/dh.go b/lib/dh.go
new file mode 100644
index 0000000..0782033
--- /dev/null
+++ b/lib/dh.go
@@ -0,0 +1,41 @@
+// Copyright © 2021 siddharth <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+import "math/big"
+
+type DH struct {
+	p  *big.Int
+	g  *big.Int
+	pk *big.Int // Private key
+}
+
+func NewDH(ps, gs string) (*DH, bool) {
+	p, ok := new(big.Int).SetString(StripSpaceChars(ps), 16)
+	if !ok {
+		return nil, false
+	}
+	g, ok := new(big.Int).SetString(StripSpaceChars(gs), 16)
+	if !ok {
+		return nil, false
+	}
+
+	// Init DH.
+	dh := new(DH)
+	dh.p = p
+	dh.g = g
+	dh.pk = big.NewInt(RandomInt(1, 10000000))
+	return dh, true
+}
+
+// Return our public key.
+func (dh *DH) Pub() *big.Int {
+	return new(big.Int).Exp(dh.g, dh.pk, dh.p)
+}
+
+// Return shared secret between us and the other party.
+// `pub` is the other party's public key.
+func (dh *DH) SharedSecret(pub *big.Int) *big.Int {
+	return new(big.Int).Exp(pub, dh.pk, dh.p)
+}