Notes

The one-time pad is considered to be a secure encryption technique as it utilizes a completely random key for each encryption. The key must be of equal length as the message and is only used once.

For instance, let's consider the following message: "HELLO". The key used for encryption could look like this: "ZYXWV". To encrypt the message, each letter of the message is combined with the corresponding letter of the key through an XOR operation (exclusive OR). The encrypted message, known as the ciphertext, would appear as: "UJJYD". The ciphertext holds no information about the original message since the key is truly random and used only once. To decrypt the message, the attacker must know the exact key used in the encryption, making the one-time pad unbreakable as long as the key remains confidential and truly random

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In cryptography, frequency analysis is the study of the frequency of letters or groups of letters in a ciphertext. The method is used as an aid to breaking substitution ciphers (e.g. mono-alphabetic substitution cipher, Caesar shift cipher, Vatsyayana cipher).

Frequency analysis consists of counting the occurrence of each letter in a text. Frequency analysis is based on the fact that, in any given piece of text, certain letters and combinations of letters occur with varying frequencies. For instance, given a section of English language, letters E, T, A and O are the most common, while letters Z, Q and X are not as frequently used.

Frequency analysis is a method used to decode encrypted messages by examining the frequency of letters or symbols in the ciphertext.
AES, or the Advanced Encryption Standard, is a symmetric-key encryption algorithm that is not susceptible to frequency analysis. AES uses a key of 128, 192, or 256 bits to encrypt data and employs a complex encryption process that includes multiple rounds to scramble the plaintext into ciphertext.
The Caesar cipher is a simple substitution cipher that replaces each letter of the plaintext with a letter shifted a specific number of positions down the alphabet. It is vulnerable to frequency analysis as the frequency of letters in the ciphertext is the same as the frequency of letters in the plaintext.
One-time pad encryption, on the other hand, uses a truly random key of equal length as the message to encrypt it, and the key is only used once. This makes it impossible to determine the original message from the ciphertext, as the key is random and secret. Hence, frequency analysis cannot be applied to one-time pad encryption.