Add dependencies/vendor (whatsapp)

vendor/go.mau.fi/libsignal/kdf/HKDF.go

@@ -0,0 +1,47 @@
+// Package kdf provides a key derivation function to calculate key output
+// and negotiate shared secrets for curve X25519 keys.
+package kdf
+
+import (
+	"crypto/sha256"
+	"io"
+
+	"golang.org/x/crypto/curve25519"
+	"golang.org/x/crypto/hkdf"
+)
+
+// HKDF is a hashed key derivation function type that can be used to derive keys.
+type HKDF func(inputKeyMaterial, salt, info []byte, outputLength int) ([]byte, error)
+
+// DeriveSecrets derives the requested number of bytes using HKDF with the given
+// input, salt, and info.
+func DeriveSecrets(inputKeyMaterial, salt, info []byte, outputLength int) ([]byte, error) {
+	kdf := hkdf.New(sha256.New, inputKeyMaterial, salt, info)
+
+	secrets := make([]byte, outputLength)
+	length, err := io.ReadFull(kdf, secrets)
+	if err != nil {
+		return nil, err
+	}
+	if length != outputLength {
+		return nil, err
+	}
+
+	return secrets, nil
+}
+
+// CalculateSharedSecret uses DH Curve25519 to find a shared secret. The result of this function
+// should be used in `DeriveSecrets` to output the Root and Chain keys.
+func CalculateSharedSecret(theirKey, ourKey [32]byte) [32]byte {
+	var sharedSecret [32]byte
+	curve25519.ScalarMult(&sharedSecret, &ourKey, &theirKey)
+
+	return sharedSecret
+}
+
+// KeyMaterial is a structure for representing a cipherkey, mac, and iv
+type KeyMaterial struct {
+	CipherKey []byte
+	MacKey    []byte
+	IV        []byte
+}