From 0629b4589459b93bc585dfbcd2775cc598dd95f8 Mon Sep 17 00:00:00 2001
From: tsousa111 <tiagao2001@hotmail.com>
Date: Thu, 18 Apr 2024 17:23:34 +0100
Subject: [PATCH] [PD1] encryptMessageContent and supporting function
 implemented

---
 .../internal/utils/cryptoUtils/cryptoUtils.go | 93 ++++++++++++++++---
 1 file changed, 78 insertions(+), 15 deletions(-)

diff --git a/Projs/PD1/internal/utils/cryptoUtils/cryptoUtils.go b/Projs/PD1/internal/utils/cryptoUtils/cryptoUtils.go
index ce91c51..f52dd52 100644
--- a/Projs/PD1/internal/utils/cryptoUtils/cryptoUtils.go
+++ b/Projs/PD1/internal/utils/cryptoUtils/cryptoUtils.go
@@ -2,13 +2,19 @@ package cryptoUtils
 
 import (
 	"PD1/internal/client"
+	"crypto"
+	"crypto/rand"
 	"crypto/rsa"
+	"crypto/sha256"
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/binary"
 	"encoding/pem"
 	"log"
 	"os"
 
+	"vendor/golang.org/x/crypto/chacha20poly1305"
+
 	"software.sslmate.com/src/go-pkcs12"
 )
 
@@ -51,26 +57,26 @@ func LoadKeyStore(keyStorePath string) KeyStore {
 	return KeyStore{cert: cert, caCertChain: caCerts, privKey: privKey}
 }
 
-func (k KeyStore)GetTLSConfig() *tls.Config {
-    certificate ,err := tls.X509KeyPair(k.cert.Raw, pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(&k.privKey)}))
-    if err!=nil{
-        log.Panicln("Could not load certificate and privkey to TLS")
-    }
-    
-    //Add the CA certificate chain to a CertPool
-    caCertPool := x509.NewCertPool()
+func (k KeyStore) GetTLSConfig() *tls.Config {
+	certificate, err := tls.X509KeyPair(k.cert.Raw, pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(&k.privKey)}))
+	if err != nil {
+		log.Panicln("Could not load certificate and privkey to TLS")
+	}
+
+	//Add the CA certificate chain to a CertPool
+	caCertPool := x509.NewCertPool()
 	for _, caCert := range k.caCertChain {
 		caCertPool.AddCert(caCert)
 	}
 
-    config := &tls.Config{
+	config := &tls.Config{
 		Certificates: []tls.Certificate{certificate},
 		ClientCAs:    caCertPool,
 	}
-    return config
+	return config
 }
 
-func (k KeyStore)GetTLSConfigServer() *tls.Config {
+func (k KeyStore) GetTLSConfigServer() *tls.Config {
 	config := k.GetTLSConfig()
 
 	config.ClientAuth = tls.RequireAndVerifyClientCert
@@ -78,15 +84,72 @@ func (k KeyStore)GetTLSConfigServer() *tls.Config {
 	return config
 }
 
-func (k KeyStore)GetTLSConfigClient() *tls.Config {
-	config:= k.GetTLSConfig()
+func (k KeyStore) GetTLSConfigClient() *tls.Config {
+	config := k.GetTLSConfig()
 
 	config.ServerName = "SERVER"
 
 	return config
 }
 
-func (k KeyStore)EncryptMessageContent(peerPubKey rsa.PublicKey, content []byte) []byte {
+func (k KeyStore) EncryptMessageContent(receiverCert *x509.Certificate, content []byte) []byte {
 	// Digital envolope
-    return nil
+
+	// Create a random symmetric key
+	dataKey := make([]byte, 32)
+	if _, err := rand.Read(dataKey); err != nil {
+		log.Panicln("Could not create dataKey properly: ", err)
+	}
+
+	cipher, err := chacha20poly1305.New(dataKey)
+	if err != nil {
+		log.Panicln("Could not create cipher: ", err)
+	}
+
+	nonce := make([]byte, cipher.NonceSize(), cipher.NonceSize()+len(content)+cipher.Overhead())
+	if _, err := rand.Read(nonce); err != nil {
+		log.Panicln("Could not create data nonce properly: ", err)
+	}
+
+	// sign the message and append the signature
+	hashedContent := sha256.Sum256(content)
+	signature, err := rsa.SignPKCS1v15(nil, &k.privKey, crypto.SHA256, hashedContent[:])
+	if err != nil {
+		log.Panicln("Could not create content signature: ", err)
+	}
+	content = pair(content, signature)
+	ciphertext := cipher.Seal(nonce, nonce, content, nil)
+
+	// crypto/rand.Reader is a good source of entropy for randomizing the
+	// encryption function.
+	receiverPubKey := receiverCert.PublicKey.(*rsa.PublicKey)
+	encryptedDataKey, err := rsa.EncryptOAEP(sha256.New(), rand.Reader, receiverPubKey, dataKey, nil)
+	if err != nil {
+		log.Panicln("Could not encrypt dataKey: ", err)
+	}
+
+	return pair(encryptedDataKey, ciphertext)
+}
+
+func (k KeyStore) DecryptMessageContent(senderCert *x509.Certificate, cipherContent []byte) []byte {
+
+   return nil
+}
+
+func pair(l []byte, r []byte) []byte {
+	length := len(l)
+	lenBytes := make([]byte, 2)
+	binary.BigEndian.PutUint16(lenBytes, uint16(length))
+
+	lWithLen := append(lenBytes, l...)
+	return append(lWithLen, r...)
+}
+
+func unPair(pair []byte) ([]byte, []byte) {
+	lenBytes := pair[:2]
+	pair = pair[2:]
+	length := binary.BigEndian.Uint16(lenBytes)
+	l := pair[:length]
+	r := pair[length:]
+	return l, r
 }