PyPadding

This package implements padding methods to use block crypto function.

Dependencies

• Python 3+

Usage

PKCS#5 / PKCS#7

• pypadding.pkcs
• Fill using number of padding number
• e.g. When block size is 8, b'hello' need 3 bytes to multiple of block size --> fill using b'\x03' (b'hello\x03\x03\x03')

>>> from pypadding import pkcs
>>> encoder = pkcs.Encoder()
>>> encoder.encode(b'hello')
b'hello\x03\x03\x03'
>>> encoder.decode(b'hello\x03\x03\x03')
b'hello'

ANSI x923

• pypadding.x923
• Fill using zero(b'\x00') and last byte set to length of padding
• e.g. When block size is 8, b'hello' need 3 bytes to multiple of block size --> fill using b'\x00' and last byte set to b'\x03' (b'hello\x00\x00\x03')

>>> from pypadding import x923
>>> encoder = x923.Encoder()
>>> encoder.encode(b'hello')
b'hello\x00\x00\x03'
>>> encoder.decode(b'hello\x00\x00\x03')
b'hello'

ISO 10126

• pypadding.iso10126
• Fill using random byte and last byte set to length of padding
• e.g. When block size is 8, b'hello' need 3 bytes to multiple of block size --> fill random byte and last byte set to b'\x03' (b'hello\x85\xaa\x03')

>>> from pypadding import iso10126
>>> encoder = iso10126.Encoder()
>>> encoder.encode(b'hello')
b'hello\x85\xaa\x03'
>>> encoder.decode(b'hello\x85\xaa\x03')
b'hello'

ISO/IEC 7816-4

• pypadding.iso7816_4
• Padding starts with b'\x80' and fill using zero b'\x00'
• e.g. When block size is 8, b'hello' need 3 bytes to multiple of block size --> fill first byte to b'\x80' then fill to b'\x00' (b'hello\x80\x00\x00')

>>> from pypadding import iso7816_4
>>> encoder = iso7816_4.Encoder()
>>> encoder.encode(b'hello')
b'hello\x80\x00\x00'
>>> encoder.decode(b'hello\x80\x00\x00')
b'hello'

Set Block Size

>>> from pypadding import pkcs
>>> encoder = pkcs.Encoder(16)
>>> encoder.encode(b'blackjack')
b'blackjack\x07\x07\x07\x07\x07\x07\x07'
>>> encoder.decode(b'blackjack\x07\x07\x07\x07\x07\x07\x07')
b'blackjack'

or

>>> from pypadding import pkcs
>>> encoder = pkcs.Encoder(block_size=16)
>>> encoder.encode(b'blackjack')
b'blackjack\x07\x07\x07\x07\x07\x07\x07'
>>> encoder.decode(b'blackjack\x07\x07\x07\x07\x07\x07\x07')
b'blackjack'

Note

• All encoded data has padding even though length of original data is multiple of block size
  • e.g. block size = 8, encoding w/ pkcs, encode('computer') --> b'computer\x08\x08\x08\x08\x08\x08\x08\x08'

Reference

• https://en.wikipedia.org/wiki/Padding_(cryptography)
  • This package implement reversible methods only