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