AATC_Crypto.py

#AATC crypto module
import codecs,recvall,ast,binascii,os,AATC_Config,time,AATC_CryptoBeta,socket
from Crypto.Cipher import AES,PKCS1_OAEP
from Crypto.PublicKey import RSA

class Crypter:
    """
    A class to encrypt and decrypt a connection with AES. Takes a connection object and mode and sets up a secret key for both participants.
    This key is then used to create an AES object which encrypts and decrypts messages via the Encrypt and Decrypt functions.
    These strings must be in binary format. The length of the string will be padded to a length multiple of 16 in size.
    The object will communicate with another Crypter object via the socket and pass public keys.
    Best for use with communication with string versions of python objects and resulting converstion using 'ast' as this will remove padding whitespace.

    If in 'CLIENT' mode the Crypter will start communication. It will send a message ('PublicKey,(Client_Public_Key,)) and the server will return the servers public key.
    The CLIENT will then send an 'Exit' message to end communication.

    Per default the Crypter will assume it should generate the keys when __init__ is called. This can be disabled by creating the object with AutoGenerate set to False.

    Mode can be changed via SetMode. Normal options are 'CLIENT' and 'SERVER'.

    """
    def __init__(self, con, mode = "CLIENT",AutoGenerate = True):
        self.con = con
        self.SetMode(mode)                
        if AutoGenerate:
            self.GenerateKey()

    def SetMode(self,mode):
        self.mode = mode

    def GenerateKey(self,key_size = AATC_Config.DEFAULT_RSA_KEYSIZE):
        print("Generating encryption keys. Please stand by...")  #Generating keys takes a long time and have found no way to shorted key length
        if self.mode == "SERVER":
            self.ServerGenerateKey()
        elif self.mode == "CLIENT":
            self.ClientGenerateKey(key_size)
        else:
            raise ValueError("Crypter: Incorrect mode set")
        print("Encryption keys generated",self.AESKey)



    def ClientGenerateKey(self,RSA_KeySize,AES_KeySize= AATC_Config.DEFAULT_AES_KEYSIZE):


        if AATC_Config.SET_ENCRYPTION_KEYS_ENABLE:   #Allows preshared encryption keys to be used 
            self.SetEncryptionKeys(AATC_Config.SET_AES_KEY, AATC_Config.SET_IV_KEY)

        elif AATC_Config.ENCRYPTION_USE_PRESHARED_KEYS:
            self.ClientPreSharedKeys(RSA_KeySize,AES_KeySize)

        else:
            self.ClientExchangeKeys(RSA_KeySize,AES_KeySize)
            

        self.Send(("Exit",()))
        Sucess,Message,Data = self.SplitData(self.Recv())
        if not Sucess:
            raise Exception("Server failed to exit"+Message)
                
                

    def ClientPreSharedKeys(self,RSA_KeySize,AES_KeySize):
        self.Send(("GetServerCertificateChain",()))
        Sucess,Message,CertificateChain = self.SplitData(self.Recv())
        if not Sucess:
            raise Exception("Server did not respond to command")

        AESKey,IV = GenerateKeys(AES_KeySize)
        PublicKey = AATC_CryptoBeta.VerifyCertificates(CertificateChain,AATC_Config.ROOT_CERTIFICATES,self.con)

        if PublicKey:
            
            PKO = PKCS1_OAEP.new(RSA.import_key(PublicKey))
            EncryptedAESKey = PKO.encrypt(AESKey)
            EncryptedIV = PKO.encrypt(IV)
            self.SetEncryptionKeys(AESKey,IV)
            self.Send(("SetKey",(EncryptedAESKey,EncryptedIV)))
            data = self.Recv()
            

        else:
            print("Certificate Chain is not valid")
            if AATC_Config.AUTO_GENERATE_FALLBACK:
                self.ClientExchangeKeys(RSA_KeySize,AES_KeySize)
            else:
                raise Exception("Certificate Chain is not valid. Exception raised")
                
            

    def ClientExchangeKeys(self,RSA_KeySize,AES_KeySize):
        RSAKey = RSA.generate(RSA_KeySize)

        privateKey = RSAKey.exportKey("DER")
        publicKey = RSAKey.publickey().exportKey("DER")

        self.Send(("GenerateKey",(publicKey,AES_KeySize)))   
        Sucess,Message,data = self.SplitData(self.Recv())     
        
        RSAPrivateKey = RSA.import_key(privateKey)
        RSAPrivateObject = PKCS1_OAEP.new(RSAPrivateKey)
        
        AESKey = RSAPrivateObject.decrypt(data[0])
        IV = RSAPrivateObject.decrypt(data[1])

        if Sucess == False:
            raise Exception("Error occured while exchanging keys")
        
        self.SetEncryptionKeys(AESKey,IV)


    ################################################################

    def ServerGenerateKey(self):

        Exit = False
        while not Exit:
            data = self.Recv()
            Command, Arguments = data[0],data[1]

            if Command == "GenerateKey":
                Sucess,Message,Data = self.ServerGenerateKeys(Arguments)

            elif Command == "GetServerCertificateChain":
                Sucess,Message,Data = self.GetServerCertificateChain(Arguments)

            elif Command == "SetKey":
                Sucess,Message,Data = self.ServerSetKey(Arguments)
                
                
            elif Command == "Exit":
                Sucess,Message,Data = True,"Exiting",[]
                Exit = True

            else:
                Sucess,Message,Data = False,"Command does not exist",[]

            self.Send((Sucess,Message,Data))




    def ServerGenerateKeys(self,Arguments):
        publicKey,AES_KeySize = Arguments[0],Arguments[1]
        
        if AES_KeySize not in AATC_Config.ALLOWED_AES_KEYSIZES:
            AES_KeySize = AATC_Config.DEFAULT_AES_KEYSIZE    #If key size is not valid set size to default of AATC_Config.DEFAULT_AES_KEYSIZE
            
        AESKey,IV = GenerateKeys(AES_KeySize)
        
        PublicKeyObject = PKCS1_OAEP.new( RSA.import_key(publicKey))
        
        EncryptedAESKey = PublicKeyObject.encrypt(AESKey)
        EncryptedIV = PublicKeyObject.encrypt(IV)

        self.SetEncryptionKeys(AESKey,IV)
        return True,"Instated encryption keys",[EncryptedAESKey,EncryptedIV]

    def GetServerCertificateChain(self,Arguments = None):
        return True,"Server Certificate Chain",AATC_Config.SERVER_CERTIFICATE_CHAIN

    def ServerSetKey(self,Arguments):
        PKO = PKCS1_OAEP.new(RSA.import_key(AATC_Config.SERVER_PRIVATE_KEY))
        AESKey,IV = Arguments[0],Arguments[1]
        AESKey,IV = PKO.decrypt(AESKey),PKO.decrypt(IV)
        self.SetEncryptionKeys(AESKey,IV)
        return True,"Keys set",[]
        




    ###############################################


    def SetEncryptionKeys(self,AESKey,IV):
        self.AESKey = AESKey
        self.IV = IV
        self.EncryptAES = AES.new(self.AESKey,AES.MODE_GCM,self.IV)    #Two seperate instances to encrypt and decrypt as non ECB AES is a stream cipher
        self.DecryptAES = AES.new(self.AESKey,AES.MODE_GCM,self.IV)    #Errors will occur if encrypt and decrypt are not equal in count.
                
                
        
        
        

        

















        
            
    def Encrypt(self,data):
        return self.EncryptAES.encrypt(data)

    def Decrypt(self,data):
        return self.DecryptAES.decrypt(data)

        
        
        
    def Send(self,data):
        self.con.sendall(codecs.encode(str(data)))
    def Recv(self):
        data = recvall.recvall(self.con)
        data = ast.literal_eval(codecs.decode(data))
        return data
    def SplitData(self,data):
        return data[0],data[1],data[2]




    
def GenerateKeys(AES_KeySize):
    AESKey = binascii.b2a_hex(os.urandom(AES_KeySize//2))  # Here to allow regeneration of AES key while still in loop if required.
    IV     = binascii.b2a_hex(os.urandom(AES_KeySize//2))
    return AESKey,IV