Assume that we have a stego ECG signal with 200 samples in which binary bits of a text message is hidden as secret message. There are 168 bits of the binary secret message. A bit is hidden in the least significant bit (LSB) of an ECG sample. Please note that the bits are embedded sequentially. For example, we have a text message “hello world”. The equivalent binary of secret message is:  011010000110010101101100011011000110111100100000011101110110111 1011100100110110001100100 Now, if we hide first 5 bits of the binary string given above in LSB of first 5 ECG samples then the resultant ECG samples will look like as follows: ECG Samples Equivalent Binary Binary After Hiding a bit in LSB -0.045 10111101001110000101000111101100 10111101001110000101000111101100 -0.055 10111101011000010100011110101110 10111101011000010100011110101111 -0.055 10111101011000010100011110101110 10111101011000010100011110101111 -0.075 10111101100110011001100110011010 10111101100110011001100110011010 -0.065 10111101100001010001111010111000 10111101100001010001111010111001 ⁞ ⁞ ⁞ You need to perform steganalysis to find out the secret text message from the stego ECG signal. In order to do this, convert each ECG samples into 64 bit binary and read corresponding LSB to store. At the end, convert retrieved bits into text.

Steganalysis is the process of detecting and analyzing hidden information in digital signals, such as ECG signals. In this case, we have a stego ECG signal with 200 samples, in which binary bits of a text message have been hidden as a secret message. The secret message consists of 168 bits, and each bit is embedded in the least significant bit (LSB) of an ECG sample.

To perform steganalysis and retrieve the hidden text message, we need to convert each ECG sample into a 64-bit binary representation and read the corresponding LSB. The LSB of each sample will give us the hidden bits. Once we have retrieved all the bits, we can convert them back into text to reveal the secret message.

Let’s take a closer look at the example given in the question. The first 5 bits of the binary string representing the secret message are “01101”. These bits are sequentially hidden in the LSB of the first 5 ECG samples.

The equivalent binary representation of the first ECG sample is “10111101001110000101000111101100”. To retrieve the hidden bit, we read the LSB, which is “0”. We repeat this process for the remaining ECG samples, and we obtain the following sequence of hidden bits:

First ECG sample: 0
Second ECG sample: 1
Third ECG sample: 1
Fourth ECG sample: 0
Fifth ECG sample: 1

Now that we have retrieved all the hidden bits, we can convert them back into text. Each group of 8 bits represents a character in ASCII encoding. Therefore, we can convert the sequence of hidden bits into the following sequence of characters:

“01101000” – ‘h’
“01100101” – ‘e’
“01101100” – ‘l’
“01101100” – ‘l’
“01101111” – ‘o’

By combining these characters, we can reconstruct the secret message: “hello”.

In summary, steganalysis involves converting each ECG sample into a 64-bit binary representation, reading the corresponding LSB to retrieve the hidden bits, and converting the retrieved bits into text. In this way, we can detect and analyze hidden information in stego ECG signals.