mirror of
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117 lines
3.0 KiB
Go
117 lines
3.0 KiB
Go
package crypto
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import (
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"crypto/rand"
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"encoding/hex"
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"errors"
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"fmt"
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"filippo.io/edwards25519"
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)
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// KeyPair holds the scalar private key and point public key
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type KeyPair struct {
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Private *edwards25519.Scalar
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Public *edwards25519.Point
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}
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// GenerateMasterKey generates a random master private key (scalar) and its public key (point)
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func GenerateMasterKey() (*KeyPair, error) {
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// 1. Generate random scalar x (32 bytes)
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var seed [64]byte
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if _, err := rand.Read(seed[:]); err != nil {
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return nil, err
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}
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x, err := edwards25519.NewScalar().SetUniformBytes(seed[:])
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if err != nil {
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return nil, err
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}
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// 2. Calculate Public Key P = x * G
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P := new(edwards25519.Point).ScalarBaseMult(x)
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return &KeyPair{Private: x, Public: P}, nil
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}
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// SplitPrivateKey takes a master private key x and returns a new random split key (r, k)
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// such that x = r + k (mod L).
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// Returns hex encoded string of r || k (64 bytes)
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func SplitPrivateKey(x *edwards25519.Scalar) (string, error) {
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// 1. Generate random r (32 bytes)
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var seed [64]byte
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if _, err := rand.Read(seed[:]); err != nil {
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return "", err
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}
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r, err := edwards25519.NewScalar().SetUniformBytes(seed[:])
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if err != nil {
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return "", err
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}
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// 2. Calculate k = x - r (mod L)
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k := new(edwards25519.Scalar).Subtract(x, r)
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// 3. Encode r and k
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rBytes := r.Bytes()
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kBytes := k.Bytes()
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full := make([]byte, 64)
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copy(full[:32], rBytes)
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copy(full[32:], kBytes)
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return hex.EncodeToString(full), nil
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}
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// RecoverPublicKey takes a split private key (r, k) or a master private key (x)
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// and returns the public key P.
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// Input can be:
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// - 32 bytes hex (Master Scalar x)
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// - 64 bytes hex (Split Key r || k)
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func RecoverPublicKey(keyHex string) (*edwards25519.Point, error) {
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keyBytes, err := hex.DecodeString(keyHex)
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if err != nil {
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return nil, fmt.Errorf("invalid hex: %w", err)
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}
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if len(keyBytes) == 32 {
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// Master Key x
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x, err := edwards25519.NewScalar().SetCanonicalBytes(keyBytes)
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if err != nil {
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return nil, fmt.Errorf("invalid scalar: %w", err)
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}
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return new(edwards25519.Point).ScalarBaseMult(x), nil
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} else if len(keyBytes) == 64 {
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// Split Key r || k
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rBytes := keyBytes[:32]
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kBytes := keyBytes[32:]
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r, err := edwards25519.NewScalar().SetCanonicalBytes(rBytes)
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if err != nil {
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return nil, fmt.Errorf("invalid scalar r: %w", err)
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}
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k, err := edwards25519.NewScalar().SetCanonicalBytes(kBytes)
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if err != nil {
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return nil, fmt.Errorf("invalid scalar k: %w", err)
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}
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// sum = r + k
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sum := new(edwards25519.Scalar).Add(r, k)
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// P = sum * G
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return new(edwards25519.Point).ScalarBaseMult(sum), nil
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}
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return nil, errors.New("invalid key length: must be 32 bytes (Master) or 64 bytes (Split)")
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}
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// EncodePoint returns the hex string of the compressed point
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func EncodePoint(p *edwards25519.Point) string {
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return hex.EncodeToString(p.Bytes())
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}
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// EncodeScalar returns the hex string of the scalar
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func EncodeScalar(s *edwards25519.Scalar) string {
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return hex.EncodeToString(s.Bytes())
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}
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