Maths and Computing:Polyalphabetic Activity

Polyalphabetic Polyalphabetic Cipher

Polyalphabetic Cipher

The Polyalphabetic Cipher is a substitution cipher.

With a shift value of n a letter is replaced with the letter that is n positions further forward

Decryption

With a shift value of n a letter is replaced with the letter that is n positions further back. Alternatively, this is the equivalent of replacing each letter with the letter that is (26 - n) positions further back

Example

The grid below shows the substution values for a shift value of 3

plaintext

ciphertext

Using different shift values

The polyalphabetic cipher has different shift values for different letter positions

In this activity, plaintext encrypted with a cipher that has three alphabets, uses shift 1 for the 1st, 4th, 7th ... letters, shift 2 for the 2nd, 5th, 8th ... letters and shift 3 for the 3rd, 6th, 9th ... letters

Polyalphabetic Cipher Question

Shift 1 = 22, Shift 2 = 24

Decode jmpclyz

Enter Answer

Shift 1 = 22, Shift 2 = 24

plaintext

alphabet 1

alphabet 2

The answer is: notepad

Polyalphabetic Cipher Question

Shift 1 = 12, Shift 2 = 9 , Shift 3 = 22

Decode bxl

Enter Answer

Shift 1 = 12, Shift 2 = 9 , Shift 3 = 22

plaintext

alphabet 1

alphabet 2

alphabet 3

The answer is: pop

Polyalphabetic Cipher Question

Shift 1 = 3, Shift 2 = 24 , Shift 3 = 17 , Shift 4 = 24

Decode vnrallx

Enter Answer

Shift 1 = 3, Shift 2 = 24 , Shift 3 = 17 , Shift 4 = 24

plaintext

alphabet 1

alphabet 2

alphabet 3

alphabet 4

Polyalphabetic

Maths and Computing:

Polyalphabetic Polyalphabetic Cipher

Polyalphabetic Cipher

The Polyalphabetic Cipher is a substitution cipher.

With a shift value of n a letter is replaced with the letter that is n positions further forward

Decryption

With a shift value of n a letter is replaced with the letter that is n positions further back. Alternatively, this is the equivalent of replacing each letter with the letter that is (26 - n) positions further back

Example

The grid below shows the substution values for a shift value of 3

Using different shift values

The polyalphabetic cipher has different shift values for different letter positions

In this activity, plaintext encrypted with a cipher that has three alphabets, uses shift 1 for the 1st, 4th, 7th ... letters, shift 2 for the 2nd, 5th, 8th ... letters and shift 3 for the 3rd, 6th, 9th ... letters

Polyalphabetic Cipher Question

Shift 1 = 22, Shift 2 = 24

Decode jmpclyz

Enter Answer

Shift 1 = 22, Shift 2 = 24

The answer is: notepad

Polyalphabetic Cipher Question

Shift 1 = 12, Shift 2 = 9 , Shift 3 = 22

Decode bxl

Enter Answer

Shift 1 = 12, Shift 2 = 9 , Shift 3 = 22

The answer is: pop

Polyalphabetic Cipher Question

Shift 1 = 3, Shift 2 = 24 , Shift 3 = 17 , Shift 4 = 24

Decode vnrallx

Enter Answer

Shift 1 = 3, Shift 2 = 24 , Shift 3 = 17 , Shift 4 = 24

The answer is: spacing

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