Bifid Cipher Tool
Plaintext
Ciphertext
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | B | I | F | D | A |
| 2 | C | E | G | H | J |
| 3 | K | L | M | N | O |
| 4 | P | Q | R | S | T |
| 5 | U | V | W | X | Y |
What is the Bifid Cipher?
The Bifid Cipher, invented by British cryptographer Barrett in the early 20th century, is an encryption algorithm that combines substitution and transposition techniques. Unlike traditional substitution ciphers, the Bifid Cipher enhances security by using a two-stage encryption process. This approach includes both replacing letters and transposing their positions, providing a higher level of security for the plaintext.
The Bifid Cipher encryption process mainly consists of two steps:
- Substitution: Letters are substituted using a letter grid (usually a 5×5 grid).
- Transposition: After substitution, the positions of the letters are further transposed, increasing the encryption's complexity.
How Does the Bifid Cipher Encrypt?
The encryption process of the Bifid Cipher can be explained through the following steps:
- Generate the Letter Grid with the Key: Using the key and the standard alphabet (A-Z), a 5×5 letter grid is generated.
- Substitution Phase: Each letter of the plaintext is replaced by its corresponding row and column numbers from the letter grid. These numbers are then recorded as coordinate pairs for each letter.
- Transposition Phase: After substitution, all the row and column numbers are separated into two sequences: one for rows and one for columns. These sequences are then placed in a table.
- Combine the New Row-Column Coordinates: The table's data is read horizontally from top to bottom, and then the coordinates are paired up.
- Generate the Ciphertext: Based on the new row-column coordinates, the corresponding letters are found in the grid to form the final ciphertext.
Example
Let's assume the plaintext is "HELLO" and the key is "KEY".
1. Generate the Letter Grid
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | K | E | Y | A | B |
| 2 | C | D | F | G | H |
| 3 | I | J | L | M | N |
| 4 | O | P | Q | R | S |
| 5 | T | U | V | W | X |
2. Obtain the Coordinates for the Plaintext
- H → (2, 5)
- E → (1, 2)
- L → (3, 3)
- L → (3, 3)
- O → (4, 1)
3. Arrange the Coordinates Vertically
| Plaintext | H | E | L | L | O |
|---|---|---|---|---|---|
| Row No. | 2 | 1 | 3 | 3 | 4 |
| Column No. | 5 | 2 | 3 | 3 | 1 |
4. Reorganize the Coordinates Horizontally and Pair Them
5. Generate the Ciphertext
- (2, 1) → C
- (3, 3) → L
- (4, 5) → S
- (2, 3) → F
- (3, 1) → I
So, the ciphertext for "HELLO" is: CLSFI.
How Does the Bifid Cipher Decrypt?
The decryption process for the Bifid Cipher is simply the reverse of encryption. After obtaining the letter coordinates from the ciphertext, the coordinates must be combined horizontally into a new string. This string is then split into two parts, forming a two-row table. The coordinates are then recombined vertically, and finally, the new coordinates are converted back into letters to restore the original plaintext.
Example
Let's assume we want to decrypt the ciphertext "CLSFI" using the key "KEY".
1. Convert the Ciphertext Characters to Coordinates
- C → (2, 1)
- L → (3, 3)
- S → (4, 5)
- F → (2, 3)
- I → (3, 1)
2. Combine the Coordinates Horizontally into a New String
3. Split the String into Two Rows and Place in a Table
| 2 | 1 | 3 | 3 | 4 |
| 5 | 2 | 3 | 3 | 1 |
4. Recombine the Coordinates Vertically
5. Decrypt the New Coordinates to Plaintext
- (2, 5) → H
- (1, 2) → E
- (3, 3) → L
- (3, 3) → L
- (4, 1) → O
Thus, the plaintext corresponding to "CLSFI" is: HELLO.