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This question concerns block cipher padding. Suppose the block cipher has a block size of 15 bytes. A certain message ends with a partial block which is 4 bytes. We must reversibly pad out the message to use some block cipher modes, such as CBC (even if the last block is full). Consider the following padding strategy. Determine the number of padding bytes required. This is a number ʼn which satisfies 1 ≤ n ≤ 15 and n + 1(P) is a multiple of 15, where 1(P) is the length of the unpadded plaintext. Pad the plaintext by appending n bytes, each with value n. Suppose the final (possibly partial) block of the message is "0x00010203" in hexadecimal. Write out the complete final block in hexadecimal. Please do not put a leading Ox as this has been written already. Ox

This question concerns block cipher padding. Suppose the block cipher has a block size of 15 bytes. A certain message ends with a partial block which is 4 bytes. We must reversibly pad out the message to use some block cipher modes, such as CBC (even if the last block is full). Consider the following padding strategy. Determine the number of padding bytes required. This is a number ʼn which satisfies 1 ≤ n ≤ 15 and n + 1(P) is a multiple of 15, where 1(P) is the length of the unpadded plaintext. Pad the plaintext by appending n bytes, each with value n. Suppose the final (possibly partial) block of the message is "0x00010203" in hexadecimal. Write out the complete final block in hexadecimal. Please do not put a leading Ox as this has been written already. Ox

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This question concerns block cipher padding. Suppose the block cipher has a block size of 15 bytes. A certain message ends with a partial block which is 4 bytes. We must reversibly pad out the message to use some block cipher modes, such as CBC (even if the last block is full). Consider the following padding strategy. Determine the number of padding bytes required. This is a number n which satisfies 1 ≤ n ≤ 15 and n + 1(P) is a multiple of 15, where 1(P) is the length of the unpadded plaintext. Pad the plaintext by appending n bytes, each with value n. Suppose the final (possibly partial) block of the message is "0x00010203" in hexadecimal. Write out the complete final block in hexadecimal. Please do not put a leading Ox as this has been written already. Ox
Transcribed Image Text:This question concerns block cipher padding. Suppose the block cipher has a block size of 15 bytes. A certain message ends with a partial block which is 4 bytes. We must reversibly pad out the message to use some block cipher modes, such as CBC (even if the last block is full). Consider the following padding strategy. Determine the number of padding bytes required. This is a number n which satisfies 1 ≤ n ≤ 15 and n + 1(P) is a multiple of 15, where 1(P) is the length of the unpadded plaintext. Pad the plaintext by appending n bytes, each with value n. Suppose the final (possibly partial) block of the message is "0x00010203" in hexadecimal. Write out the complete final block in hexadecimal. Please do not put a leading Ox as this has been written already. Ox
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