Final answer:
To encrypt the message using a tabular transposition cipher with rows of 7 characters, the message 'at four head east to trenches' is laid out and padded with 'a's. After rearranging, the encrypted message is 'ahtsetnfaotoeeourancrradsh tes taaa'.
Step-by-step explanation:
The student's question involves the use of a tabular transposition cipher to encrypt a message. First, the message 'at four head east to trenches' is laid out in rows of seven characters each, result in extra spaces that should be padded with 'a's to complete the blocks if necessary:
at four
head ea
st to tr
enchesa
Next, each row of text is written under each other, and the columns run as the cipher text, giving us the following encrypted message:
ahtsetn
faotoee
ourancr
radsh t
es taaa
The spaces are ignored, so the final encrypted message reads 'ahtsetnfaotoeeourancrradsh tes taaa'.
A tabular transposition cipher is a method of rearranging the letters in a message according to a specific pattern. In this case, the rows of the table have a length of 7 characters. To encrypt the message 'four head east to trenches', we can first divide it into blocks of 7 characters: 'four he', 'ad east', ' to tre', and 'nchesaa'.
Next, we rearrange the letters within each block according to the specified pattern. Applying the pattern to each block, we get: 'urf heo', 'das tae', 'ort et', and 'csenhay'.
Finally, we combine the blocks and remove any extra padding. The encrypted message is 'urf heo das tae ort et csenhay'.