SymmetricCrypto Class

Properties   Methods   Events   Config Settings   Errors  

The SymmetricCrypto class provides capabilities of encrypting and decrypting binary data.

Syntax

class secureblackbox.SymmetricCrypto

Remarks

SymmetricCrypto allows you to encrypt and decrypt uninterpreted binary data with a symmetric block encryption cipher.

SymmetricCrypto is one of the low-level cryptography classes (alongside PublicKeyCrypto and HashFunction) offered by SecureBlackbox. It allows to encrypt pools of binary data with a chosen symmetric encryption cipher. It can be used as a standalone encryption mechanism (for example, for encrypting database data or setting files), or as part of a larger security system (such as PKCS#7 or PGP).

Encryption and decryption with SymmetricCrypto broadly consists of three steps: configuring the encryption parameters, setting up the key material, and actually encrypting or decrypting the data.

Configuring encryption parameters

When preparing SymmetricCrypto for action, you need to fine-tune several cryptographic encryption parameters. Normally these would be given to you by the party that expects you to encrypt or decrypt their data (for example: 'AES128-CBC, with the IV of all zeroes').

As a rule, the following parameters need to be selected/adjusted:

• encryption_algorithm, such as AES128, 3DES, or Blowfish.
• Encryption mode, such as CBC, CTR, GCM or CCM.
• Block padding for data lengths that are not multiples of the cipher's block size (none, PKCS5, or ANXI X9.23).
• tag_size (for AEAD algorithms only).
• hash_algorithm and mac_algorithm (for algorithms that require them).

Setting up the key material

Symmetric algorithms use short (typically, 16-32 bytes) encryption keys. The exact key length depends on the encryption algorithm used (for example, 16 bytes for AES128). You can use the key_size property to learn the expected key length for the chosen encryption_algorithm.

In addition to keys, many encryption modes require additional data. These are typically represented by an Initialization Vector (IV) and a nonce. The IV is a randomized public part of the encryption key, which is used to avoid re-use of the same encryption key for different data. Nonce is similar in meaning to the initialization vector, but applies to the algorithm and not the key.

Any key material that you assign to SymmetricCrypto should be first loaded into the CryptoKeyManager object. Once you have done that, simply assign the key object returned by the CryptoKeyManager to the key property. Note that while the IV needs to be provided to the CryptoKeyManager, the Nonce needs to be assigned directly to nonce property of the SymmetricCrypto object.

Note that CryptoKeyManager lets you to form the encryption key in a few ways: by loading it from memory or file, generating a new random key, or deriving it from a password. Use the method that is the most appropriate in your circumstances.

Encrypting and decrypting data

Now that the component has been set up, you can proceed to the actual encryption or decryption operation. There are a few options you can use here:

• Encrypt (or decrypt) a buffer to a buffer using encrypt (decrypt).
• Encrypt a file to a file using encrypt_file.
• Encrypt a stream to a stream using encrypt_stream.
• Encrypt longer data chunk by chunk using a sequence of encrypt_init, encrypt_update, encrypt_update, ..., encrypt_update, encrypt_final calls.

If you are using an authenticated encryption algorithm that can take additional associated data (AEAD), you can provide that via the associated_data property.

Please find an example of using SymmetricCrypto to encrypt and decrypt a file below: //encrypting a file SymmetricCrypto symmetricCrypto = new SymmetricCrypto(); symmetricCrypto.setEncryptionAlgorithm("RC4"); // default AES256 // generating a key from a password CryptoKeyManager keyManager = new CryptoKeyManager(); keyManager.deriveKey(256, "MyPassword",""); keyManager.getKey().setIV(new byte[16]); symmetricCrypto.setKey(keyManager.getKey()); // the encoding to apply to the output data, default cetDefault which depends on // the operation and type of key being used symmetricCrypto.setOutputEncoding(SymmetricCrypto.cetBinary); // first parameter is the path of the file you want to encrypt and the second is the path // of where the encrypted file will be saved symmetricCrypto.encryptFile("./message.txt","encryptedFile.bin"); // decrypting a file symmetricCrypto.reset(); symmetricCrypto.setKey(keyManager.getKey()); // first parameter is the path of the file you want to decrypt and the second is the path // of where the decrypted file will be saved symmetricCrypto.decryptFile("encryptedFile.bin","decryptedFile.bin");

Property List

---

The following is the full list of the properties of the class with short descriptions. Click on the links for further details.

Method List

---

The following is the full list of the methods of the class with short descriptions. Click on the links for further details.

Event List

---

The following is the full list of the events fired by the class with short descriptions. Click on the links for further details.

Config Settings

---

The following is a list of config settings for the class with short descriptions. Click on the links for further details.

associated_data Property

Provides Associated Data for AEAD algorithms.

Syntax

def get_associated_data() -> bytes: ...
def set_associated_data(value: bytes) -> None: ...

associated_data = property(get_associated_data, set_associated_data)

Remarks

Use this property to set up Associated Data for AEAD encryption algorithms.

block_size Property

The block size of the chosen symmetric cipher.

Syntax

def get_block_size() -> int: ...

block_size = property(get_block_size, None)

Default Value

0

Remarks

This property returns the block size of the chosen symmetric cipher.

Modern symmetric algorithms typically use blocks of 16 bytes. Some older algorithms, such as DES or Blowfish, use 8-byte blocks.

This property is read-only.

encryption_algorithm Property

The encryption algorithm to use for encrypting the data.

Syntax

def get_encryption_algorithm() -> str: ...
def set_encryption_algorithm(value: str) -> None: ...

encryption_algorithm = property(get_encryption_algorithm, set_encryption_algorithm)

Default Value

"AES256"

Remarks

This property specifies the base symmetric algorithm to use (e.g. AES128). Use it in conjunction with mode to set up the complete encryption scheme (such as AES128-CBC or AES128-GCM).

fips_mode Property

Reserved.

Syntax

def get_fips_mode() -> bool: ...
def set_fips_mode(value: bool) -> None: ...

fips_mode = property(get_fips_mode, set_fips_mode)

Default Value

FALSE

Remarks

This property is reserved for future use.

hash_algorithm Property

The hash algorithm to use during encryption.

Syntax

def get_hash_algorithm() -> str: ...
def set_hash_algorithm(value: str) -> None: ...

hash_algorithm = property(get_hash_algorithm, set_hash_algorithm)

Default Value

"SHA256"

Remarks

Use this property to provide the hash algorithm to be used with the encryption operation. This only applies to certain encryption algorithms/modes.

input_encoding Property

The encoding to apply to the input data.

Syntax

def get_input_encoding() -> int: ...
def set_input_encoding(value: int) -> None: ...

input_encoding = property(get_input_encoding, set_input_encoding)

Default Value

0

Remarks

key_handle Property

Allows to get or set a 'handle', a unique identifier of the underlying property object.

Syntax

def get_key_handle() -> int: ...
def set_key_handle(value: int) -> None: ...

key_handle = property(get_key_handle, set_key_handle)

Default Value

0

Remarks

Allows to get or set a 'handle', a unique identifier of the underlying property object. Use this property to assign objects of the same type in a quicker manner, without copying them fieldwise.

When you pass a handle of one object to another, the source object is copied to the destination rather than assigned. It is safe to get rid of the original object after such operation. pdfSigner.setSigningCertHandle(certMgr.getCertHandle());

key_key Property

The byte array representation of the key.

Syntax

def get_key_key() -> bytes: ...

key_key = property(get_key_key, None)

Remarks

The byte array representation of the key. This may not be available for non-key_exportable keys.

This property is read-only.

key_size Property

Returns the cryptographic key size in bytes.

Syntax

def get_key_size() -> int: ...

key_size = property(get_key_size, None)

Default Value

0

Remarks

Use this property to read the cryptographic key size. For the majority of the symmetric algorithms this is hard-coded in the algorithm itself (such as 16 bytes for AES128), but may be variable for certain exceptions, such as Blowfish or RC4.

This property is read-only.

mac_algorithm Property

The (H)MAC algorithm to use during encryption.

Syntax

def get_mac_algorithm() -> str: ...
def set_mac_algorithm(value: str) -> None: ...

mac_algorithm = property(get_mac_algorithm, set_mac_algorithm)

Default Value

""

Remarks

Use this property to configure the HMAC algorithm to use with the encryption operation. This only applies to a small subset of algorithms/modes.

mode Property

Specifies the symmetric cipher mode of operation.

Syntax

def get_mode() -> int: ...
def set_mode(value: int) -> None: ...

mode = property(get_mode, set_mode)

Default Value

0

Remarks

Use this property to specify the mode of operation as required by your environment. The default setting is CBC.

nonce Property

Specifies the Nonce value to employ.

Syntax

def get_nonce() -> bytes: ...
def set_nonce(value: bytes) -> None: ...

nonce = property(get_nonce, set_nonce)

Remarks

Use this property to specify the Nonce value for the symmetric operation. Not every algorithm or mode uses nonce.

output_encoding Property

The encoding to apply to the output data.

Syntax

def get_output_encoding() -> int: ...
def set_output_encoding(value: int) -> None: ...

output_encoding = property(get_output_encoding, set_output_encoding)

Default Value

0

Remarks

padding Property

The padding type to apply to the encrypted data.

Syntax

def get_padding() -> int: ...
def set_padding(value: int) -> None: ...

padding = property(get_padding, set_padding)

Default Value

1

Remarks

Use this property to specify the padding type to use with the encrypted data. A padding type commonly used in modern security environments is PKCS#5.

payload_size Property

Specifies the payload size, in bytes.

Syntax

def get_payload_size() -> int: ...
def set_payload_size(value: int) -> None: ...

payload_size = property(get_payload_size, set_payload_size)

Default Value

0

Remarks

Use this property to specify the size of the input data in bytes. This is only used by a subset of algorithms/modes, such as CCM.

stream_cipher Property

Returns true if the selected algorithms works as a stream cipher.

Syntax

def get_stream_cipher() -> bool: ...

stream_cipher = property(get_stream_cipher, None)

Default Value

FALSE

Remarks

This property returns true if the selected algorithm processes data as a stream (byte-by-byte), rather than block-by-block. This affects the need to use a proper padding settings.

This property is read-only.

tag_size Property

Specifies the AEAD tag size, in bytes.

Syntax

def get_tag_size() -> int: ...
def set_tag_size(value: int) -> None: ...

tag_size = property(get_tag_size, set_tag_size)

Default Value

16

Remarks

Use this property to specify/customize the tag size for AEAD encryption.

config Method

Sets or retrieves a configuration setting.

Syntax

def config(configuration_string: str) -> str: ...

Remarks

config is a generic method available in every class. It is used to set and retrieve configuration settings for the class.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

decrypt Method

Decrypts a buffer.

Syntax

def decrypt(buffer: bytes) -> bytes: ...

Remarks

Use this method to decrypt a byte array and get the encrypted message in another byte array.

Specify the decryption key in key property.

decrypt_file Method

Decrypts a file.

Syntax

def decrypt_file(source_file: str, dest_file: str) -> None: ...

Remarks

Use this method to decrypt an encrypted file and save the decrypted data to another file.

Specify the decryption key in key property before calling this method.

decrypt_final Method

Finalization of decryption by blocks.

Syntax

def decrypt_final() -> bytes: ...

Remarks

Use this method to finalize of decryption by blocks.

Specify decryption key in key property.

decrypt_init Method

Initializes a per-block decryption process.

Syntax

def decrypt_init() -> None: ...

Remarks

Use this method to start a block-by-block decryption process.

Specify the decryption key in key property before starting the decryption.

decrypt_update Method

Decrypts the next block of encrypted data.

Syntax

def decrypt_update(buffer: bytes) -> bytes: ...

Remarks

When using block-by-block decryption, pass every subsequent block of the encrypted message to this method until the entire message is processed. For each encrypted block the method returns a piece of decrypted data.

Please note that in general case there is no direct correspondence between the data actually contained in the encrypted block with the output of this method. The component may choose to cache a piece of the provided buffer internally if it doesn't constitute a full block of encrypted data.

Remember to call decrypt_init before calling this method to prepare the control for the decryption process.

do_action Method

Performs an additional action.

Syntax

def do_action(action_id: str, action_params: str) -> str: ...

Remarks

do_action is a generic method available in every class. It is used to perform an additional action introduced after the product major release. The list of actions is not fixed, and may be flexibly extended over time.

The unique identifier (case insensitive) of the action is provided in the ActionID parameter.

ActionParams contains the value of a single parameter, or a list of multiple parameters for the action in the form of PARAM1=VALUE1;PARAM2=VALUE2;....

Common ActionIDs:

encrypt Method

Encrypts a buffer.

Syntax

def encrypt(buffer: bytes) -> bytes: ...

Remarks

Use this method to encrypt a byte array and get the protected message in another byte array.

Specify the encryption key in key property before calling this method.

This is a one-off encryption method. Don't use it with granular per-block methods (encrypt_init, encrypt_update, encrypt_final).

encrypt_file Method

Encrypts a file.

Syntax

def encrypt_file(source_file: str, dest_file: str) -> None: ...

Remarks

Use this method to encrypt a file and save the protected message in another file.

Specify the encryption key in key property before commencing encryption.

encrypt_final Method

Finalization of encryption by blocks.

Syntax

def encrypt_final() -> bytes: ...

Remarks

Use this method to finalize of encryption by blocks.

Specify encryption key in key property.

encrypt_init Method

Initializes a per-block encryption process.

Syntax

def encrypt_init() -> None: ...

Remarks

Use this method to initialize a block-by-block encryption process. Follow it with calls to encrypt_update (as many as needed), and complete the encryption with an encrypt_final call.

Specify the encryption key in key property before calling this method.

encrypt_update Method

Encrypts the next block of data.

Syntax

def encrypt_update(buffer: bytes) -> bytes: ...

Remarks

Use this method to encrypt the next block of data contained in Buffer.

Call this method after calling encrypt_init for as many times as needed, until the whole volume of data is processed. Having done that, call encrypt_final to complete the encryption and get the terminating encrypted trailer.

reset Method

Resets the class settings.

Syntax

def reset() -> None: ...

Remarks

reset is a generic method available in every class.

on_error Event

Reports errors during encryption or decryption.

Syntax

class SymmetricCryptoErrorEventParams(object):
  @property
  def error_code() -> int: ...

  @property
  def description() -> str: ...

# In class SymmetricCrypto:
@property
def on_error() -> Callable[[SymmetricCryptoErrorEventParams], None]: ...
@on_error.setter
def on_error(event_hook: Callable[[SymmetricCryptoErrorEventParams], None]) -> None: ...

Remarks

class fires this event in case of exceptional conditions during a cryptographic operation.

ErrorCode contains an error code and Description contains a textual description of the error.

on_notification Event

This event notifies the application about an underlying control flow event.

Syntax

class SymmetricCryptoNotificationEventParams(object):
  @property
  def event_id() -> str: ...

  @property
  def event_param() -> str: ...

# In class SymmetricCrypto:
@property
def on_notification() -> Callable[[SymmetricCryptoNotificationEventParams], None]: ...
@on_notification.setter
def on_notification(event_hook: Callable[[SymmetricCryptoNotificationEventParams], None]) -> None: ...

Remarks

The class fires this event to let the application know about some event, occurrence, or milestone in the class. For example, it may fire to report completion of the document processing. The list of events being reported is not fixed, and may be flexibly extended over time.

The unique identifier of the event is provided in the EventID parameter. EventParam contains any parameters accompanying the occurrence. Depending on the type of the class, the exact action it is performing, or the document being processed, one or both may be omitted.

on_progress Event

Reports the data encryption/decryption progress.

Syntax

class SymmetricCryptoProgressEventParams(object):
  @property
  def total() -> int: ...

  @property
  def current() -> int: ...

  @property
  def cancel() -> bool: ...
  @cancel.setter
  def cancel(value) -> None: ...

# In class SymmetricCrypto:
@property
def on_progress() -> Callable[[SymmetricCryptoProgressEventParams], None]: ...
@on_progress.setter
def on_progress(event_hook: Callable[[SymmetricCryptoProgressEventParams], None]) -> None: ...

Remarks

This event fires periodically during a file encrypt/decrypt operation to report its progress.

Use the Cancel parameter to terminate the encryption/decryption if needed.

SymmetricCrypto Config Settings

The class accepts one or more of the following configuration settings. Configuration settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the config method.

SymmetricCrypto Config Settings

Base Config Settings

SymmetricCrypto Errors

SymmetricCrypto Errors