# Tag Info

3

The answer depends on how you would layer the encryption on top of the existing protocol. If you implemented your own Skype client, you could deal with compression issues yourself. That might allow you to use format preserving encryption, perhaps on the compressed data stream and not the audio itself. However, you would need to be careful – speech ...

3

If you want $N$ serial numbers, your serial numbers will have to use $n$ bits for uniqueness, where $n = \log_2 N$. So if you have 100 bits to use for the serial, you could use 20 to get about a million serials and have 80 bits to use for a cryptographic MAC or signature. Now there are two approaches, the symmetric and the asymmetric. In the symmetric ...

7

What happens if the sender is at another point in the sequence? ... the key is pressed while out of range to the car. In a rolling code (code hopping) system, the keyfob transmitter maintains a synchronization counter C, incremented every time a button is pushed. The car receiver stores the most recent validated synchronization counter it has received ...

3

In a rolling code both the sender and the receiver always move forward in the sequence. If the sender has sent the $n$th code, then it will send the $(n+1)$th next. Contrarily, if the receiver has seen the $n$th code it will only accept the $(n+1)$th code or some later code. What happens if the sender is at another point in the sequence? Think of that ...

0

You cannot ensure this - at least not against an determined attacker. Depending on the platform the app runs you might get some more assurance (think "TPM with metered boot"), but as soon as the attackers have control over the device they can circumvent it - even when your app is confined in a smartcard or similiar rigidly protected device.

1

Is there a vastly simpler way? I think so. Let the server send a reset token in the following form: (deadline, HMAC(server key, id_user || S || deadline)) That is, the server calculates an authenticator that allows id_user to change their secret from S before deadline. The key used should be only known by the server and can be changed often, since ...

0

$\;\;\;$ Probably as long as you compare securely, although you're applying $\;\;\;$ a pbkdf to what should be a uniformly random long secret key. $\;\;\;$ Don't bother computing S'; let S be a uniformly random secret key and use it instead. $\;\;\;$ To construct a reset token for a user U, set h = HMAC(S, 0 || (id,U,e) ), $\;\;\;$ set H = HMAC(S,1||h), ...

1

It doesn't work without further restrictions. For simplification, let's assume Alice encrypts a bunch of files but doesn't have to send all of them to Bob. She can still decide to re-order the files or leave out some. Then she can encode the secret shared key between Alice and Bob in the least significant bits of the ciphertexts without changing the files. ...

0

What you want is a protocol where Alice sends a message to Bob without being able to control any ciphertext bits. This would be possible if either The message and encryption are completely deterministic and give Alice no freedom to choose between two ciphertexts, or Alice is unable to predict the ciphertext without sending a message. The first could be ...

0

If you can use something more lightweight than pairings then you should skip pairings. There is a technical property of pairings than is not the case with other crypto primitives. And this is the evaluation of multiplications on the exponent that cannot be achieved in other cases. If you need some sort of summation then you encode in the exponent and then ...

2

Pairings in cryptography is a very important tool, the introduction of which has developed a new field, that is pairing-based cryptography. After the independent pioneering work by Joux and by Sakai et al.("Cryptosystems based on pairing"), many pairing-based crypto-systems emerged. In cryptography, pairings are often treated as "black-box", and then we ...

2

Well, hope that it's not late for this answer. Because it was yesterday that I encountered this problem and I'm new to this wonderful website. According to your description, and as far as I know, this protocol meets your demands very well. First, it works with RSA as you have mentioned in the second paragraph. The original version of this protocol is ...

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