asyncua.crypto.security_policies

Complexity

Total Complexity

102

Size/Duplication

Total Lines	622
Duplicated Lines	23.95 %

Importance

Changes

0

74 Methods

Rating	Name	Duplication	Size	Complexity
A	VerifierHMac256.verify()	0	4	2
A	SignerHMac256.__init__()	0	3	1
A	Cryptography.min_padding_size()	0	4	2
A	VerifierAesCbc.verify()	0	4	2
A	SignerAesCbc.signature()	0	2	1
A	Cryptography.verify()	0	2	1
A	SecurityPolicyBasic256.__init__()	21	21	2
A	EncryptorAesCbc.__init__()	0	3	1
A	EncryptorRsa.__init__()	0	6	1
A	VerifierSha256.signature_size()	0	2	1
A	Cryptography.signature()	0	2	1
A	DecryptorAesCbc.decrypt()	0	2	1
A	Encryptor.plain_block_size()	0	3	1
A	VerifierHMac256.signature_size()	0	2	1
A	VerifierRsa.verify()	0	2	1
A	Encryptor.encrypted_block_size()	0	3	1
A	Cryptography.encrypted_block_size()	0	7	2
A	DecryptorAesCbc.__init__()	0	3	1
A	SecurityPolicyBasic128Rsa15.encrypt_asymmetric()	3	3	1
A	Verifier.verify()	0	3	1
A	VerifierSha256.__init__()	0	4	1
A	SignerRsa.signature()	0	2	1
A	Decryptor.decrypt()	0	3	1
A	SecurityPolicyBasic128Rsa15.make_remote_symmetric_key()	6	6	1
A	SignerAesCbc.signature_size()	0	2	1
A	Cryptography.decrypt()	0	4	2
A	SecurityPolicyBasic256.make_local_symmetric_key()	7	7	1
A	EncryptorAesCbc.encrypt()	0	2	1
A	SignerHMac256.signature()	0	2	1
A	Encryptor.encrypt()	0	3	1
A	SignerAesCbc.__init__()	0	3	1
A	SecurityPolicyBasic128Rsa15.make_local_symmetric_key()	6	6	1
A	VerifierRsa.__init__()	0	4	1
A	Cryptography.remove_padding()	0	8	3
A	SignerRsa.signature_size()	0	2	1
A	Cryptography.signature_size()	0	2	1
A	Cryptography.__init__()	0	9	2
A	Signer.signature()	0	3	1
A	SecurityPolicyBasic256.make_remote_symmetric_key()	8	8	1
A	Cryptography.encrypt()	0	6	3
A	SecurityPolicyBasic256Sha256.encrypt_asymmetric()	0	3	1
A	Cryptography.plain_block_size()	0	7	2
A	SignerHMac256.signature_size()	0	2	1
A	EncryptorRsa.encrypt()	0	7	2
A	DecryptorAesCbc.plain_block_size()	0	2	1
A	DecryptorRsa.plain_block_size()	0	2	1
A	Cryptography.vsignature_size()	0	2	1
A	Signer.signature_size()	0	3	1
A	SignerSha256.__init__()	0	4	1
A	VerifierHMac256.__init__()	0	3	1
A	EncryptorAesCbc.encrypted_block_size()	0	2	1
A	EncryptorAesCbc.plain_block_size()	0	2	1
A	DecryptorAesCbc.encrypted_block_size()	0	2	1
A	DecryptorRsa.__init__()	0	6	1
A	Cryptography.padding()	0	17	5
A	DecryptorRsa.encrypted_block_size()	0	2	1
A	VerifierAesCbc.signature_size()	0	2	1
A	SignerRsa.__init__()	0	4	1
A	VerifierSha256.verify()	0	2	1
A	EncryptorRsa.plain_block_size()	0	2	1
A	VerifierRsa.signature_size()	0	2	1
A	SignerSha256.signature_size()	0	2	1
A	SecurityPolicyBasic256.encrypt_asymmetric()	3	3	1
A	SignerSha256.signature()	0	2	1
A	Verifier.signature_size()	0	3	1
A	EncryptorRsa.encrypted_block_size()	0	2	1
A	Decryptor.plain_block_size()	0	3	1
A	SecurityPolicyBasic128Rsa15.__init__()	21	21	2
A	Decryptor.encrypted_block_size()	0	3	1
A	VerifierAesCbc.__init__()	0	3	1
A	DecryptorRsa.decrypt()	0	7	2
A	SecurityPolicyBasic256Sha256.__init__()	0	24	3
A	SecurityPolicyBasic256Sha256.make_local_symmetric_key()	0	7	1
A	SecurityPolicyBasic256Sha256.make_remote_symmetric_key()	0	8	1

import logging
import struct

from abc import ABCMeta, abstractmethod
from ..ua import CryptographyNone, SecurityPolicy, MessageSecurityMode, UaError

try:
    from ..crypto import uacrypto
    CRYPTOGRAPHY_AVAILABLE = True
except ImportError:
    CRYPTOGRAPHY_AVAILABLE = False


POLICY_NONE_URI = 'http://opcfoundation.org/UA/SecurityPolicy#None'


def require_cryptography(obj):
    """
    Raise exception if cryptography module is not available.
    Call this function in constructors.
    """
    if not CRYPTOGRAPHY_AVAILABLE:
        raise UaError(f"Can't use {obj.__class__.__name__}, cryptography module is not installed")


class Signer(object):
    """
    Abstract base class for cryptographic signature algorithm
    """

    __metaclass__ = ABCMeta

    @abstractmethod
    def signature_size(self):
        pass

    @abstractmethod
    def signature(self, data):
        pass


class Verifier(object):
    """
    Abstract base class for cryptographic signature verification
    """

    __metaclass__ = ABCMeta

    @abstractmethod
    def signature_size(self):
        pass

    @abstractmethod
    def verify(self, data, signature):
        pass


class Encryptor(object):
    """
    Abstract base class for encryption algorithm
    """

    __metaclass__ = ABCMeta

    @abstractmethod
    def plain_block_size(self):
        pass

    @abstractmethod
    def encrypted_block_size(self):
        pass

    @abstractmethod
    def encrypt(self, data):
        pass


class Decryptor(object):
    """
    Abstract base class for decryption algorithm
    """

    __metaclass__ = ABCMeta

    @abstractmethod
    def plain_block_size(self):
        pass

    @abstractmethod
    def encrypted_block_size(self):
        pass

    @abstractmethod
    def decrypt(self, data):
        pass


class Cryptography(CryptographyNone):
    """
    Security policy: Sign or SignAndEncrypt
    """

    def __init__(self, mode=MessageSecurityMode.Sign):
        self.Signer = None
        self.Verifier = None
        self.Encryptor = None
        self.Decryptor = None
        if mode not in (MessageSecurityMode.Sign,
                        MessageSecurityMode.SignAndEncrypt):
            raise ValueError(f"unknown security mode {mode}")
        self.is_encrypted = (mode == MessageSecurityMode.SignAndEncrypt)

    def plain_block_size(self):
        """
        Size of plain text block for block cipher.
        """
        if self.is_encrypted:
            return self.Encryptor.plain_block_size()
        return 1

    def encrypted_block_size(self):
        """
        Size of encrypted text block for block cipher.
        """
        if self.is_encrypted:
            return self.Encryptor.encrypted_block_size()
        return 1

    def padding(self, size):
        """
        Create padding for a block of given size.
        plain_size = size + len(padding) + signature_size()
        plain_size = N * plain_block_size()
        """
        if not self.is_encrypted:
            return b''
        block_size = self.Encryptor.plain_block_size()
        extrapad_size = 2 if self.Encryptor.encrypted_block_size() > 256 else 1
        rem = (size + self.signature_size() + extrapad_size) % block_size
        if rem != 0:
            rem = block_size - rem
        data = bytes(bytearray([rem % 256])) * (rem + 1)
        if self.Encryptor.encrypted_block_size() > 256:
            data = data + bytes(bytearray([rem >> 8]))
        return data

    def min_padding_size(self):
        if self.is_encrypted:
            return 1
        return 0

    def signature_size(self):
        return self.Signer.signature_size()

    def signature(self, data):
        return self.Signer.signature(data)

    def vsignature_size(self):
        return self.Verifier.signature_size()

    def verify(self, data, sig):
        self.Verifier.verify(data, sig)

    def encrypt(self, data):
        if self.is_encrypted:
            if not len(data) % self.Encryptor.plain_block_size() == 0:
                raise ValueError
            return self.Encryptor.encrypt(data)
        return data

    def decrypt(self, data):
        if self.is_encrypted:
            return self.Decryptor.decrypt(data)
        return data

    def remove_padding(self, data):
        if self.is_encrypted:
            if self.Decryptor.encrypted_block_size() > 256:
                pad_size = struct.unpack('<h', data[-2:])[0] + 2
            else:
                pad_size = bytearray(data[-1:])[0] + 1
            return data[:-pad_size]
        return data


class SignerRsa(Signer):

    def __init__(self, client_pk):
        require_cryptography(self)
        self.client_pk = client_pk
        self.key_size = self.client_pk.key_size // 8

    def signature_size(self):
        return self.key_size

    def signature(self, data):
        return uacrypto.sign_sha1(self.client_pk, data)


class VerifierRsa(Verifier):

    def __init__(self, server_cert):
        require_cryptography(self)
        self.server_cert = server_cert
        self.key_size = self.server_cert.public_key().key_size // 8

    def signature_size(self):
        return self.key_size

    def verify(self, data, signature):
        uacrypto.verify_sha1(self.server_cert, data, signature)


class EncryptorRsa(Encryptor):

    def __init__(self, server_cert, enc_fn, padding_size):
        require_cryptography(self)
        self.server_cert = server_cert
        self.key_size = self.server_cert.public_key().key_size // 8
        self.encryptor = enc_fn
        self.padding_size = padding_size

    def plain_block_size(self):
        return self.key_size - self.padding_size

    def encrypted_block_size(self):
        return self.key_size

    def encrypt(self, data):
        encrypted = b''
        block_size = self.plain_block_size()
        for i in range(0, len(data), block_size):
            encrypted += self.encryptor(self.server_cert.public_key(),
                                        data[i: i + block_size])
        return encrypted


class DecryptorRsa(Decryptor):

    def __init__(self, client_pk, dec_fn, padding_size):
        require_cryptography(self)
        self.client_pk = client_pk
        self.key_size = self.client_pk.key_size // 8
        self.decryptor = dec_fn
        self.padding_size = padding_size

    def plain_block_size(self):
        return self.key_size - self.padding_size

    def encrypted_block_size(self):
        return self.key_size

    def decrypt(self, data):
        decrypted = b''
        block_size = self.encrypted_block_size()
        for i in range(0, len(data), block_size):
            decrypted += self.decryptor(self.client_pk,
                                        data[i: i + block_size])
        return decrypted


class SignerAesCbc(Signer):

    def __init__(self, key):
        require_cryptography(self)
        self.key = key

    def signature_size(self):
        return uacrypto.sha1_size()

    def signature(self, data):
        return uacrypto.hmac_sha1(self.key, data)


class VerifierAesCbc(Verifier):

    def __init__(self, key):
        require_cryptography(self)
        self.key = key

    def signature_size(self):
        return uacrypto.sha1_size()

    def verify(self, data, signature):
        expected = uacrypto.hmac_sha1(self.key, data)
        if signature != expected:
            raise uacrypto.InvalidSignature


class EncryptorAesCbc(Encryptor):

    def __init__(self, key, init_vec):
        require_cryptography(self)
        self.cipher = uacrypto.cipher_aes_cbc(key, init_vec)

    def plain_block_size(self):
        return self.cipher.algorithm.key_size // 8

    def encrypted_block_size(self):
        return self.cipher.algorithm.key_size // 8

    def encrypt(self, data):
        return uacrypto.cipher_encrypt(self.cipher, data)


class DecryptorAesCbc(Decryptor):

    def __init__(self, key, init_vec):
        require_cryptography(self)
        self.cipher = uacrypto.cipher_aes_cbc(key, init_vec)

    def plain_block_size(self):
        return self.cipher.algorithm.key_size // 8

    def encrypted_block_size(self):
        return self.cipher.algorithm.key_size // 8

    def decrypt(self, data):
        return uacrypto.cipher_decrypt(self.cipher, data)


class SignerSha256(Signer):

    def __init__(self, client_pk):
        require_cryptography(self)
        self.client_pk = client_pk
        self.key_size = self.client_pk.key_size // 8

    def signature_size(self):
        return self.key_size

    def signature(self, data):
        return uacrypto.sign_sha256(self.client_pk, data)


class VerifierSha256(Verifier):

    def __init__(self, server_cert):
        require_cryptography(self)
        self.server_cert = server_cert
        self.key_size = self.server_cert.public_key().key_size // 8

    def signature_size(self):
        return self.key_size

    def verify(self, data, signature):
        uacrypto.verify_sha256(self.server_cert, data, signature)


class SignerHMac256(Signer):

    def __init__(self, key):
        require_cryptography(self)
        self.key = key

    def signature_size(self):
        return uacrypto.sha256_size()

    def signature(self, data):
        return uacrypto.hmac_sha256(self.key, data)


class VerifierHMac256(Verifier):

    def __init__(self, key):
        require_cryptography(self)
        self.key = key

    def signature_size(self):
        return uacrypto.sha256_size()

    def verify(self, data, signature):
        expected = uacrypto.hmac_sha256(self.key, data)
        if signature != expected:
            raise uacrypto.InvalidSignature


class SecurityPolicyBasic128Rsa15(SecurityPolicy):

This code seems to be duplicated in your project.

    """
    DEPRECATED, do not use anymore!

    Security Basic 128Rsa15
    A suite of algorithms that uses RSA15 as Key-Wrap-algorithm
    and 128-Bit (16 bytes) for encryption algorithms.
    - SymmetricSignatureAlgorithm - HmacSha1
      (http://www.w3.org/2000/09/xmldsig#hmac-sha1)
    - SymmetricEncryptionAlgorithm - Aes128
      (http://www.w3.org/2001/04/xmlenc#aes128-cbc)
    - AsymmetricSignatureAlgorithm - RsaSha1
      (http://www.w3.org/2000/09/xmldsig#rsa-sha1)
    - AsymmetricKeyWrapAlgorithm - KwRsa15
      (http://www.w3.org/2001/04/xmlenc#rsa-1_5)
    - AsymmetricEncryptionAlgorithm - Rsa15
      (http://www.w3.org/2001/04/xmlenc#rsa-1_5)
    - KeyDerivationAlgorithm - PSha1
      (http://docs.oasis-open.org/ws-sx/ws-secureconversation/200512/dk/p_sha1)
    - DerivedSignatureKeyLength - 128 (16 bytes)
    - MinAsymmetricKeyLength - 1024 (128 bytes)
    - MaxAsymmetricKeyLength - 2048 (256 bytes)
    - CertificateSignatureAlgorithm - Sha1

    If a certificate or any certificate in the chain is not signed with
    a hash that is Sha1 or stronger then the certificate shall be rejected.
    """

    URI = "http://opcfoundation.org/UA/SecurityPolicy#Basic128Rsa15"
    signature_key_size = 16
    symmetric_key_size = 16
    AsymmetricEncryptionURI = "http://www.w3.org/2001/04/xmlenc#rsa-1_5"
    AsymmetricSignatureURI = "http://www.w3.org/2000/09/xmldsig#rsa-sha1"

    @staticmethod
    def encrypt_asymmetric(pubkey, data):
        return uacrypto.encrypt_rsa15(pubkey, data)

    def __init__(self, server_cert, client_cert, client_pk, mode):
        logger = logging.getLogger(__name__)
        logger.warning("DEPRECATED! Do not use SecurityPolicyBasic128Rsa15 anymore!")

        require_cryptography(self)
        if isinstance(server_cert, bytes):
            server_cert = uacrypto.x509_from_der(server_cert)
        # even in Sign mode we need to asymmetrically encrypt secrets
        # transmitted in OpenSecureChannel. So SignAndEncrypt here
        self.asymmetric_cryptography = Cryptography(
            MessageSecurityMode.SignAndEncrypt)
        self.asymmetric_cryptography.Signer = SignerRsa(client_pk)
        self.asymmetric_cryptography.Verifier = VerifierRsa(server_cert)
        self.asymmetric_cryptography.Encryptor = EncryptorRsa(
            server_cert, uacrypto.encrypt_rsa15, 11)
        self.asymmetric_cryptography.Decryptor = DecryptorRsa(
            client_pk, uacrypto.decrypt_rsa15, 11)
        self.symmetric_cryptography = Cryptography(mode)
        self.Mode = mode
        self.server_certificate = uacrypto.der_from_x509(server_cert)
        self.client_certificate = uacrypto.der_from_x509(client_cert)

    def make_local_symmetric_key(self, secret, seed):
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha1(secret, seed, key_sizes)
        self.symmetric_cryptography.Signer = SignerAesCbc(sigkey)
        self.symmetric_cryptography.Encryptor = EncryptorAesCbc(key, init_vec)

    def make_remote_symmetric_key(self, secret, seed):
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha1(secret, seed, key_sizes)
        self.symmetric_cryptography.Verifier = VerifierAesCbc(sigkey)
        self.symmetric_cryptography.Decryptor = DecryptorAesCbc(key, init_vec)


class SecurityPolicyBasic256(SecurityPolicy):

This code seems to be duplicated in your project.

    """
    DEPRECATED, do not use anymore!

    Security Basic 256
    A suite of algorithms that are for 256-Bit (32 bytes) encryption,
    algorithms include:
    - SymmetricSignatureAlgorithm - HmacSha1
      (http://www.w3.org/2000/09/xmldsig#hmac-sha1)
    - SymmetricEncryptionAlgorithm - Aes256
      (http://www.w3.org/2001/04/xmlenc#aes256-cbc)
    - AsymmetricSignatureAlgorithm - RsaSha1
      (http://www.w3.org/2000/09/xmldsig#rsa-sha1)
    - AsymmetricKeyWrapAlgorithm - KwRsaOaep
      (http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p)
    - AsymmetricEncryptionAlgorithm - RsaOaep
      (http://www.w3.org/2001/04/xmlenc#rsa-oaep)
    - KeyDerivationAlgorithm - PSha1
      (http://docs.oasis-open.org/ws-sx/ws-secureconversation/200512/dk/p_sha1)
    - DerivedSignatureKeyLength - 192 (24 bytes)
    - MinAsymmetricKeyLength - 1024 (128 bytes)
    - MaxAsymmetricKeyLength - 2048 (256 bytes)
    - CertificateSignatureAlgorithm - Sha1

    If a certificate or any certificate in the chain is not signed with
    a hash that is Sha1 or stronger then the certificate shall be rejected.
    """

    URI = "http://opcfoundation.org/UA/SecurityPolicy#Basic256"
    signature_key_size = 24
    symmetric_key_size = 32
    AsymmetricEncryptionURI = "http://www.w3.org/2001/04/xmlenc#rsa-oaep"
    AsymmetricSignatureURI = "http://www.w3.org/2000/09/xmldsig#rsa-sha1"

    @staticmethod
    def encrypt_asymmetric(pubkey, data):
        return uacrypto.encrypt_rsa_oaep(pubkey, data)

    def __init__(self, server_cert, client_cert, client_pk, mode):
        logger = logging.getLogger(__name__)
        logger.warning("DEPRECATED! Do not use SecurityPolicyBasic256 anymore!")

        require_cryptography(self)
        if isinstance(server_cert, bytes):
            server_cert = uacrypto.x509_from_der(server_cert)
        # even in Sign mode we need to asymmetrically encrypt secrets
        # transmitted in OpenSecureChannel. So SignAndEncrypt here
        self.asymmetric_cryptography = Cryptography(
            MessageSecurityMode.SignAndEncrypt)
        self.asymmetric_cryptography.Signer = SignerRsa(client_pk)
        self.asymmetric_cryptography.Verifier = VerifierRsa(server_cert)
        self.asymmetric_cryptography.Encryptor = EncryptorRsa(
            server_cert, uacrypto.encrypt_rsa_oaep, 42)
        self.asymmetric_cryptography.Decryptor = DecryptorRsa(
            client_pk, uacrypto.decrypt_rsa_oaep, 42)
        self.symmetric_cryptography = Cryptography(mode)
        self.Mode = mode
        self.server_certificate = uacrypto.der_from_x509(server_cert)
        self.client_certificate = uacrypto.der_from_x509(client_cert)

    def make_local_symmetric_key(self, secret, seed):
        # specs part 6, 6.7.5
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha1(secret, seed, key_sizes)
        self.symmetric_cryptography.Signer = SignerAesCbc(sigkey)
        self.symmetric_cryptography.Encryptor = EncryptorAesCbc(key, init_vec)

    def make_remote_symmetric_key(self, secret, seed):

        # specs part 6, 6.7.5
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha1(secret, seed, key_sizes)
        self.symmetric_cryptography.Verifier = VerifierAesCbc(sigkey)
        self.symmetric_cryptography.Decryptor = DecryptorAesCbc(key, init_vec)


class SecurityPolicyBasic256Sha256(SecurityPolicy):
    """
    Security Basic 256Sha256
    A suite of algorithms that uses Sha256 as Key-Wrap-algorithm
    and 256-Bit (32 bytes) for encryption algorithms.

    - SymmetricSignatureAlgorithm_HMAC-SHA2-256
      https://tools.ietf.org/html/rfc4634
    - SymmetricEncryptionAlgorithm_AES256-CBC
      http://www.w3.org/2001/04/xmlenc#aes256-cbc
    - AsymmetricSignatureAlgorithm_RSA-PKCS15-SHA2-256
      http://www.w3.org/2001/04/xmldsig-more#rsa-sha256
    - AsymmetricEncryptionAlgorithm_RSA-OAEP-SHA1
      http://www.w3.org/2001/04/xmlenc#rsa-oaep
    - KeyDerivationAlgorithm_P-SHA2-256
      http://docs.oasis-open.org/ws-sx/ws-secureconversation/200512/dk/p_sha256
    - CertificateSignatureAlgorithm_RSA-PKCS15-SHA2-256
      http://www.w3.org/2001/04/xmldsig-more#rsa-sha256
    - Basic256Sha256_Limits
        -> DerivedSignatureKeyLength: 256 bits
        -> MinAsymmetricKeyLength: 2048 bits
        -> MaxAsymmetricKeyLength: 4096 bits
        -> SecureChannelNonceLength: 32 bytes
    """

    URI = "http://opcfoundation.org/UA/SecurityPolicy#Basic256Sha256"
    signature_key_size = 32
    symmetric_key_size = 32
    AsymmetricEncryptionURI = "http://www.w3.org/2001/04/xmlenc#rsa-oaep"
    AsymmetricSignatureURI = "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"

    @staticmethod
    def encrypt_asymmetric(pubkey, data):
        return uacrypto.encrypt_rsa_oaep(pubkey, data)

    def __init__(self, peer_cert, host_cert, client_pk, mode,
                 permission_ruleset=None):
        require_cryptography(self)
        if isinstance(peer_cert, bytes):
            peer_cert = uacrypto.x509_from_der(peer_cert)
        # even in Sign mode we need to asymmetrically encrypt secrets
        # transmitted in OpenSecureChannel. So SignAndEncrypt here
        self.asymmetric_cryptography = Cryptography(
            MessageSecurityMode.SignAndEncrypt)
        self.asymmetric_cryptography.Signer = SignerSha256(client_pk)
        self.asymmetric_cryptography.Verifier = VerifierSha256(peer_cert)
        self.asymmetric_cryptography.Encryptor = EncryptorRsa(
            peer_cert, uacrypto.encrypt_rsa_oaep, 42)
        self.asymmetric_cryptography.Decryptor = DecryptorRsa(
            client_pk, uacrypto.decrypt_rsa_oaep, 42)
        self.symmetric_cryptography = Cryptography(mode)
        self.Mode = mode
        self.peer_certificate = uacrypto.der_from_x509(peer_cert)
        self.host_certificate = uacrypto.der_from_x509(host_cert)
        if permission_ruleset is None:
            from asyncua.crypto.permission_rules import SimpleRoleRuleset
            permission_ruleset = SimpleRoleRuleset()
        
        self.permissions = permission_ruleset

    def make_local_symmetric_key(self, secret, seed):
        # specs part 6, 6.7.5
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha256(secret, seed, key_sizes)
        self.symmetric_cryptography.Signer = SignerHMac256(sigkey)
        self.symmetric_cryptography.Encryptor = EncryptorAesCbc(key, init_vec)

    def make_remote_symmetric_key(self, secret, seed):

        # specs part 6, 6.7.5
        key_sizes = (self.signature_key_size, self.symmetric_key_size, 16)

        (sigkey, key, init_vec) = uacrypto.p_sha256(secret, seed, key_sizes)
        self.symmetric_cryptography.Verifier = VerifierHMac256(sigkey)
        self.symmetric_cryptography.Decryptor = DecryptorAesCbc(key, init_vec)


def encrypt_asymmetric(pubkey, data, policy_uri):
    """
    Encrypt data with pubkey using an asymmetric algorithm.
    The algorithm is selected by policy_uri.
    Returns a tuple (encrypted_data, algorithm_uri)
    """
    for cls in [SecurityPolicyBasic256Sha256, SecurityPolicyBasic256, SecurityPolicyBasic128Rsa15]:
        if policy_uri == cls.URI:
            return (cls.encrypt_asymmetric(pubkey, data),
                    cls.AsymmetricEncryptionURI)
    if not policy_uri or policy_uri == POLICY_NONE_URI:
        return data, ''
    raise UaError(f"Unsupported security policy `{policy_uri}`")