Frequency Hoping spread spectrum question

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Discussion Overview

The discussion revolves around the implementation and security aspects of Frequency Hopping Spread Spectrum (FHSS) technology. Participants explore how the algorithms for frequency changes are communicated between base stations and mobile terminals, and the implications for security and data interception.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether the frequency change algorithm is transmitted at the start of the conversation, suggesting that knowledge of this algorithm is necessary for interception.
  • Another participant indicates that the implementation of FHSS can vary, drawing a parallel to historical cryptographic methods.
  • Some participants propose two main variations regarding the algorithm: either it is a known construction parameter or it is transmitted at the beginning of the conversation.
  • A third variation is introduced, suggesting that the algorithm may only be updated when the mobile is connected to the base station.
  • There is a discussion about whether the algorithm must be transmitted back to the mobile station, with some uncertainty expressed about the working solutions.
  • One participant notes that not all FHSS implementations are designed for security, with some focusing on interference immunity instead.
  • Another participant emphasizes that fixed channel sequences in simple implementations do not provide security, and that encryption techniques should be used for serious security measures.
  • A historical note is made about the invention of frequency-hopping technology by Heddy Lamar and George Antheil, highlighting its initial military application.

Areas of Agreement / Disagreement

Participants express differing views on the security implications of FHSS implementations, with some arguing that fixed sequences lack security while others suggest that not all implementations are intended for secure communication. The discussion remains unresolved regarding the specifics of how algorithms are communicated and their impact on security.

Contextual Notes

Participants mention various implementations and their intended purposes, but there is no consensus on the specifics of algorithm transmission or security effectiveness. The discussion reflects a range of assumptions and conditions that may affect the understanding of FHSS technology.

dervast
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Hi to everyone.. I am just reading an artical abouts FHSS... as it describes the frequency hoping adds security to the system cause u must know the algorithm for the frequency changes:)
Unfortunately the article doesn't mention if this algorithm is transmitted at the start of the conversasion betwwen the Base station and the mobile terminal . If that is true then i should only attend the transmission from the beginning so i should have the algorithm for the frequency changes. Do u think i am correct or not?
Thx a lot
 
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I'm sure it varies from system to system. I imagine it could be similar to the 'enigma' used by Germany in WW2.
 
What do u mean it varies from system to system? I can find here only 2 different variations
a)the algorithm is known from before (a construction parameter) so if i want to steal data from a wireless link i wii always know in which frequencies i would find data
b)The algorithm is always transmitted at the start of the conversation .. so if i want to steal data i only have to start capturing frames at the beginning of conversation so i can capture the algorithm being used too
 
c) The algorithm is only updated when the mobile is connected to the base station.
 
c)so it must be transmitted back to the mobile station... Right? Do u know if that is the working solution?
 
Not transmitted. Physical link mobile/base.

For some things. Don't know if it's all cases.
 
There is no single implementation of FHSS. Some simple implementations use channel sequences that are fixed in both the transmitter and receiver. More advanced implementations use cryptographic protocols and a form of secret-sharing to configure the transmitter and receiver before data transmission begins.

- Warren
 
"Some simple implementations use channel sequences that are fixed in both the transmitter and receiver. " If they are fixed then the implementation provides no security.. Do u think that i am correct?
 
Not all FHSS implementations are intended to be secure -- some are just intended to be immune to interference.

- Warren
 
  • #10
dervast said:
"Some simple implementations use channel sequences that are fixed in both the transmitter and receiver. " If they are fixed then the implementation provides no security.. Do u think that i am correct?
Very little security against a determined hacker, true. They are mainly used for tolerance of noise, not for security. You use encryption techniques as chroot said for the FH sequence, as well as encrypting the data, if you are serious about keeping you out. Er, sorry, I meant keeping out hackers.
 
  • #11
By the way, Heddy Lamar and George Antheil invented this technology. Ms Lamar had been married to a weapons manufacturer who also designed control systems, and apparently she was a quick study. The mechanical system they designed to control frequency-hopping (intended to prevent jamming of guided torpedoes) was pretty much ignored by the Navy brass until Sylvania picked it up over a decade later, using electronics, not coded mechanical rolls.
 

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