A farm irrigation controller sends an encrypted alert when soil moisture is too low. Fig. 1 shows a trace from the controller program. The plaintext alert w...
Question 1 Report
A farm irrigation controller sends an encrypted alert when soil moisture is too low. Fig. 1 shows a trace from the controller program. The plaintext alert word is processed one character at a time using a Caesar key of 3. Table 1 contains moisture readings from three sensor zones and the ciphertext produced for their alert files. The grower needs to identify the alert that was created from the correct encryption algorithm.
Fig. 1: program trace
| Zone | Moisture (%) | Plaintext alert | Ciphertext alert |
|---|---|---|---|
| North | 18 | DRY | GUB |
| East | 21 | DRY | GUB |
| West | 16 | DRY | GXB |
Table 1: irrigation alert data
(a) State the key used by the controller program. [1]
(b) Identify the zone with the lowest moisture reading. [1]
(c) Identify the ciphertext that is not correct. [1]
(d) Use Fig. 1 to write the correct ciphertext for DRY. [3]
Answer Details
(a) The controller key is 3 [1].
(b) The lowest moisture reading is 16%, so the zone is West [1].
(c) The incorrect ciphertext is GXB [1]. A shift of 3 must map R to U, not X.
(d) D becomes G [1], R becomes U [1], and Y becomes B after wrapping through Z [1]. Thus DRY encrypts to GUB [3].
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