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6

Signature generation is not encryption with the private key. Still, the basic flow of what you describe is correct for signature generation. However, the verification step is where everything derails. As indicated in the comments, it is impossible to reverse a cryptographic hash. However, for signature verification, it is assumed that the verifying party ...

5

For the problem as stated in the question, yes what's asked is possible, exactly per the method stated in the question. For textbook RSA (except with unusually tolerant decryption code), no, that's not possible. For RSA as practiced, there exists solutions or not, and it can be found on not, depending on methods and parameters. The critical differences are ...

3

Like Ray, I'd like to point out that if the PINs are not chosen randomly but selected by humans and there is no rejection of the easiest pins, the same rules as for passwords apply: some are very, very, very common. This analysis of 4-digit pins shows that 3 tries will allow you to break over 18% of 4-digit pins, not the 0.03% you would expect from the ...

1

Steam ciphers work by encrypting the counter / nonce with the master key (generated from a cryptographically secure psuedo-random number generator). For example with AES in CTR mode, you would run the usual AES Encryption algorithm, but instead of inputting a message you input the counter/ nonce. This creates a stream. A portion of the stream equal to the ...

1

It uses an artifact of pairings over groups of composite order. Specifically, if the order of $G$ is $p_1$ and the order of $H$ is $p_3$ and $p_1, p_3$ are relatively prime, then $e(G, H) = 1$. This can be easily seen by considering the order of $e(G, H)$; we know that $e(G, H)^{p_1} = e(G^{p_1}, H) = e(1, H) = 1$, hence the order of $e(G, H)$ must be a ...

1

The answer depends on the size of the plaintext you are attacking and the number of ciphertext blocks you have. Assume that you have a 64-bit block-sized cipher named C64 and 128-bit block cipher named C128. If you know that the $m$ is smaller than 64-bit than you will have only one ciphertext for C64 and C128. There is a need for padding at the end of the ...

1

Sender encrypts the message with private key and sends his/her public key and the receiver decrypts by using sender's public key and vice versa. No, you cannot encrypt (for confidentiality) using a private key; anybody with the public key can decrypt after all. Now how this is RSA or AES? Because the message should be encrypted by receiver's public key ...

1

In order to prove data integrity - I think this is what you mean rather that symmetric authentication - you can use a symmetric key with HMAC/KMAC. These are varieties of message authentication codes, and these specific varieties use hash algorithms - SHA2/3/SHAKE. I'll use the example of AES-CTR with HMAC. To generate keys for this, use the HKDF-Expand, to ...

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