**Given Data:**

** **Plain text : xABBB

Key : x0FFF

**Solution (Encryption):**

- Let us consider the universal ASSCII values for the total character set between NULL to DEL (ie) 0 to 127 (Decimal values) respectively.
- Now we form a table for the Plain text, Key and their corresponding ASSCII values.

S.No |
Plain text |
ASSCII Value |
Key |
ASSCII Value |

1 | x | 120 | x | 120 |

2 | A | 65 | 0 | 48 |

3 | B | 66 | F | 70 |

4 | B | 66 | F | 70 |

5 | B | 66 | F | 70 |

- Now add the ASSCII values of Key and Plain text.
- Mod the obtained values by the greatest value in the series, in this care 127.
- The corresponding character of the obtained ASSCII values obtained gives out the Encrypted Text.

S.No |
Sum of ASCII Values |
Sum (mod) 127 |
Character |

1 | 240 | 113 | q |

2 | 113 | 113 | q |

3 | 136 | 9 | TAB(horizontal TAB) |

4 | 136 | 9 | TAB(horizontal TAB) |

5 | 136 | 9 | TAB(horizontal TAB) |

- Hence the encrypted text is given by “
**qq**“according to ASSCII Conversion.

**Solution (Decryption):**

The encrypted text is “qq “and the Key is “x0FFF”.

- A table is made for the ASCII values of the encrypted text and the Key.

S.No |
Encrypted Text |
ASSCII Value |
Key |
ASSCII Value |

1 | q | 113 | x | 120 |

2 | q | 113 | 0 | 48 |

3 | TAB | 9 | F | 70 |

4 | TAB | 9 | F | 70 |

5 | TAB | 9 | F | 70 |

- find the sum of ASCII value and 127 to form the Modifies Encrypted text
- Now find the difference between the ASCII Values.
- Find the value of ASCII difference (mod) 127.
- Find the corresponding character for the value obtained.

S.No |
ASSCII value of ET+127 |
Key ASSCII |
ASCII difference |
ASCII difference (mod) 127 |
Character |

1 | 240 | 120 | 120 | 120 | x |

2 | 240 | 48 | 192 | 65 | A |

3 | 136 | 70 | 66 | 66 | B |

4 | 136 | 70 | 66 | 66 | B |

5 | 136 | 70 | 66 | 66 | B |

- Hence the original text is “
**xABBB**”