In a mono alphabetic cipher, each alphabet in the plain text is replaced by a corresponding alphabet to produce cipher text.

The given message is “This is an easy problem”.

**Steps to encode the message:**

1. Consider the mono alphabetic cipher in the figure 8.3

2. Replace each letter in the plaintext with corresponding cipher text letter given in the figure.

3. The obtained message is the required encoded cipher text.

Therefore, the encoded message is “**uasi si mj cmiw lokngch.**”

The given message is “rmij’u uamu xyj”.

**Steps to decode the message:**

1. Consider the mono alphabetic cipher in the figure 8.3

2. Replace each letter in the cipher text with corresponding plain text letter given in the figure.

3. The obtained message is the required decoded message.

Therefore, the decoded message is “**wasn’t that fun**”.

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