chore: Seperate code into multiple files for client and server.

server/utils.go

@@ -0,0 +1,69 @@
+package server
+
+import (
+	"crypto/cipher"
+	"crypto/rand"
+	"fmt"
+	"net"
+
+	"github.com/ProtonMail/gopenpgp/v3/crypto"
+)
+
+func (bismuth BismuthServer) encryptMessage(aead cipher.AEAD, msg []byte) ([]byte, error) {
+	nonce := make([]byte, aead.NonceSize(), aead.NonceSize()+len(msg)+aead.Overhead())
+
+	if _, err := rand.Read(nonce); err != nil {
+		return []byte{}, err
+	}
+
+	encryptedMsg := aead.Seal(nonce, nonce, msg, nil)
+	return encryptedMsg, nil
+}
+
+func (bismuth BismuthServer) decryptMessage(aead cipher.AEAD, encMsg []byte) ([]byte, error) {
+	if len(encMsg) < aead.NonceSize() {
+		return []byte{}, fmt.Errorf("ciphertext too short")
+	}
+
+	// Split nonce and ciphertext.
+	nonce, ciphertext := encMsg[:aead.NonceSize()], encMsg[aead.NonceSize():]
+
+	// Decrypt the message and check it wasn't tampered with.
+	decryptedData, err := aead.Open(nil, nonce, ciphertext, nil)
+
+	if err != nil {
+		return []byte{}, err
+	}
+
+	return decryptedData, nil
+}
+
+// Initializes a Bismuth server.
+//
+// Both `pubKey` and `privKey` are armored PGP public and private keys respectively.
+func NewBismuthServer(pubKey string, privKey string, signServers []string, encryptionAlgo int, connHandler func(conn net.Conn) error) (*BismuthServer, error) {
+	publicKey, err := crypto.NewKeyFromArmored(pubKey)
+
+	if err != nil {
+		return nil, err
+	}
+
+	privateKey, err := crypto.NewKeyFromArmored(privKey)
+
+	if err != nil {
+		return nil, err
+	}
+
+	pgp := crypto.PGP()
+
+	bismuth := BismuthServer{
+		PublicKey:                    publicKey,
+		PrivateKey:                   privateKey,
+		HandleConnection:             connHandler,
+		SigningServers:               signServers,
+		SymmetricEncryptionAlgorithm: encryptionAlgo,
+		pgp:                          pgp,
+	}
+
+	return &bismuth, nil
+}