M209 Class

Naturally, the m209 library includes a class that simulates a M-209 converter. The M209 class allows you to experiment with all moving parts of an M-209, including encrypting and decrypting messages. Keep in mind there is a higher level class, StdProcedure, that encapsulates all the steps of the standard encrypting and decrypting operations, including generating indicators and placing or removing them from messages. However if you need lower-level access or you are inventing your own procedures, you would use the M209 class directly.

class m209.converter.M209([lugs=None[, pin_list=None]])

The M209 class takes the following optional arguments.

Parameters:

M209 objects have the following attributes.

letter_count

This attribute represents the letter counter functionality. It is an integer that is incremented after every letter is encrypted or decrypted. It may be set to any integer value or examined at any time.

M209 objects support the following methods.

set_pins(n, effective_pins)

Sets the pin settings on the specified key wheel n.

Parameters:

  • n – an integer between 0-5, inclusive. Key wheel 0 is the left-most wheel and wheel 5 is the right-most.

  • effective_pins – an iterable of letters whose pins are slid to the “effective” position (to the right). See Key wheel pin settings.

set_all_pins(pin_list)

Sets all key wheel pins according to the supplied pin list.

Parameters:

pin_list – must either be None or a 6-element list of strings where each string element is as described in Key wheel pin settings. If None, all pins in all key wheels are moved to the ineffective position.

set_drum_lugs(lug_list)

Sets the drum lugs according to the given lug_list parameter.

If lug_list is None or empty, all lugs will be placed in neutral positions.

Otherwise, the lug_list can either be a list or a string.

If lug_list is passed a list, it must be a list of 1 or 2-tuple integers, where each integer is between 0-5, inclusive, and represents a 0-based key wheel position. The list can not be longer than 27 items. Only lug bars with lugs in non-neutral positions need be listed. Lug bars with one lug in a non-neutral position are represented by a 1-tuple. Bars with 2 non-netural lugs are represented as a 2-tuple.

If lug_list is passed as a string, it is assumed to be in key list format as described in Lug settings format.

Example:

m = M209()
m.set_drum_lugs('1-0 2-0*2 0-3 0-5*3 0-6 2-4 3-6')

# or equivalently
m.set_drum_lugs([(0, ), (1, ), (1, ), (2, ), (4, ), (4, ), (4, ), (5, ), (1, 3), (2, 5)])
set_key_wheel(n, c)

Set key wheel n to the letter c.

Parameters:

  • n – an integer between 0-5 where key wheel 0 is the leftmost key wheel, and 5 is the rightmost

  • c – a 1-letter string valid for key wheel n

Raises:

KeyWheelError – if c is not valid for wheel n

set_key_wheels(s)

Set the key wheels from left to right to the six letter string s.

Raises:

KeyWheelError – if any letter in s is not valid for the corresponding key wheel

set_random_key_wheels()

Sets the six key wheels to random letters.

Returns:

a string of length six representing the new key wheel settings

get_settings()

Returns the current key settings.

Returns:

a named tuple of (lugs, pin_list) representing the current key settings. lugs will be in string format.

encrypt(plaintext[, group=True[, spaces=True]])

Performs an encrypt operation on the given plaintext and returns the encrypted ciphertext as a string.

Parameters:

  • plaintext – the text string to encrypt

  • group – if True, the ciphertext string will be grouped into 5-letter groups, separated by spaces

  • spaces – if True, space characters in the input plaintext will automatically be treated as Z characters. Otherwise spaces in the plaintext will raise an M209Error.

Returns:

the ciphertext as a string

decrypt(ciphertext[, spaces=True[, z_sub=True]])

Performs a decrypt operation on the given ciphertext and returns the decrypted plaintext as a string.

Parameters:

  • ciphertext – the text string to decyrpt

  • spaces – if True, spaces will be allowed in the input ciphertext and ignored. Otherwise space characters will raise an M209Error. This is useful if the input ciphertext is in 5-letter groups, separated by spaces.

  • z_sub – if True, Z characters in the output plaintext will be replaced by space characters, just like an actual M-209.

Returns:

the plaintext as a string

Example:

>>> from m209.converter import M209
>>> m = M209()
>>> m.set_drum_lugs('1-0 2-0*2 0-3 0-5*3 0-6 2-4 3-6')
>>> pin_list = [
...     'FGIKOPRSUVWYZ',
...     'DFGKLMOTUY',
...     'ADEFGIORTUVX',
...     'ACFGHILMRSU',
...     'BCDEFJKLPS',
...     'EFGHIJLMNP'
... ]
>>> m.set_all_pins(pin_list)
>>> m.set_key_wheels('FFEGJP')
>>> ct = m.encrypt('THE PIZZA HAS ARRIVED')
>>> ct
'QBCHU WCCDI YFNCH LOZJY G'
>>> m.set_key_wheels('FFEGJP')
>>> pt = m.decrypt(ct)
>>> pt
'THE PI  A HAS ARRIVED'