feat: implement key generation, encryption, and decryption functions with tests

hsp/crypt.go

@@ -0,0 +1,90 @@
+package hsp
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"io"
+
+	"golang.org/x/crypto/curve25519"
+)
+
+type KeyPair struct {
+	Private [32]byte
+	Public  [32]byte
+}
+
+func NewKeyPair(publicKey, privateKey [32]byte) *KeyPair {
+	return &KeyPair{
+		Public:  publicKey,
+		Private: privateKey,
+	}
+}
+
+func GenerateKeyPair() (pair *KeyPair, err error) {
+	privateKey := make([]byte, 32)
+	publicKey := make([]byte, 32)
+	_, err = rand.Read(privateKey[:])
+	if err != nil {
+		return
+	}
+
+	privateKey[0] &= 248
+	privateKey[31] &= 127
+	privateKey[31] |= 64
+
+	curve25519.ScalarBaseMult((*[32]byte)(publicKey), (*[32]byte)(privateKey))
+	return NewKeyPair([32]byte(publicKey), [32]byte(privateKey)), nil
+}
+
+func DeriveSharedKey(privateKey, peerPublicKey [32]byte) (sharedKey [32]byte, err error) {
+	generated, err := curve25519.X25519(privateKey[:], peerPublicKey[:])
+	if err != nil {
+		return
+	}
+
+	sharedKey = [32]byte(generated)
+
+	return
+}
+
+func Encrypt(key []byte, data []byte) (encrypted []byte, nonce []byte, err error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	aesGCM, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	nonce = make([]byte, aesGCM.NonceSize())
+	_, err = io.ReadFull(rand.Reader, nonce)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	encrypted = aesGCM.Seal(nil, nonce, data, nil)
+
+	return encrypted, nonce, nil
+}
+
+func Decrypt(key []byte, nonce []byte, encrypted []byte) (data []byte, err error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	aesGCM, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err = aesGCM.Open(nil, nonce, encrypted, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}