initial import

core/codec/dh.go

@@ -0,0 +1,88 @@
+package codec
+
+import (
+	"crypto/rand"
+	"errors"
+	"math/big"
+)
+
+// see https://www.zhihu.com/question/29383090/answer/70435297
+// see https://www.ietf.org/rfc/rfc3526.txt
+// 2048-bit MODP Group
+
+var (
+	ErrInvalidPriKey    = errors.New("invalid private key")
+	ErrInvalidPubKey    = errors.New("invalid public key")
+	ErrPubKeyOutOfBound = errors.New("public key out of bound")
+
+	p, _ = new(big.Int).SetString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
+	g, _ = new(big.Int).SetString("2", 16)
+	zero = big.NewInt(0)
+)
+
+type DhKey struct {
+	PriKey *big.Int
+	PubKey *big.Int
+}
+
+func ComputeKey(pubKey, priKey *big.Int) (*big.Int, error) {
+	if pubKey == nil {
+		return nil, ErrInvalidPubKey
+	}
+
+	if pubKey.Sign() <= 0 && p.Cmp(pubKey) <= 0 {
+		return nil, ErrPubKeyOutOfBound
+	}
+
+	if priKey == nil {
+		return nil, ErrInvalidPriKey
+	}
+
+	return new(big.Int).Exp(pubKey, priKey, p), nil
+}
+
+func GenerateKey() (*DhKey, error) {
+	var err error
+	var x *big.Int
+
+	for {
+		x, err = rand.Int(rand.Reader, p)
+		if err != nil {
+			return nil, err
+		}
+
+		if zero.Cmp(x) < 0 {
+			break
+		}
+	}
+
+	key := new(DhKey)
+	key.PriKey = x
+	key.PubKey = new(big.Int).Exp(g, x, p)
+
+	return key, nil
+}
+
+func NewPublicKey(bs []byte) *big.Int {
+	return new(big.Int).SetBytes(bs)
+}
+
+func (k *DhKey) Bytes() []byte {
+	if k.PubKey == nil {
+		return nil
+	}
+
+	byteLen := (p.BitLen() + 7) >> 3
+	ret := make([]byte, byteLen)
+	copyWithLeftPad(ret, k.PubKey.Bytes())
+
+	return ret
+}
+
+func copyWithLeftPad(dst, src []byte) {
+	padBytes := len(dst) - len(src)
+	for i := 0; i < padBytes; i++ {
+		dst[i] = 0
+	}
+	copy(dst[padBytes:], src)
+}