but a sealed letter has the expectaion of privacy that only the addressee will open it
postcards and unencrypted radio transmissions (like say 2.4 ghz or 900 mhz cordless phones, and fm & am radio) do not carry such an expectation, so it is not illegal to snoop such traffic (this is one of the reasons why cable and satellite tv is encrypted (ie scrambled); were it not encrypted in some fashion, it would be legal to set up your own equipment to capture the stream and do what yoou what with it like you do with fm and am radio).
encrypting the data, like putting something in a sealed, addressed envelope, lets everyone know that the data is not intended for anyone to read and creates an expectation of privacy. the ease of decrypting data is not really relevant (eg breaking a wep protected connection carries the same legal penalties as breaking a wpa2 protected connection) because the basis for the law against reading others' mail is the violation of a privacy that the victim took steps to create (eg its almost certainly legal to read others' postcards and definitely legal to read the outside of the envelope because no steps are taken to prevent anyone other than the intended recipient from reading the message).
you could argue that there is also an expectation of privacy inherent in the relevant link (for wifi and ethernet) layers of the networking stack since the standards call for ignoring all frames not addressed to you (a host on the network), but this argument is severely weakened by the fact that frames are sent to every host connected to the network and that determining whether you should be reading a given frame requires you to read the frame (and not just part of it, because FCS is over the whole frame, not just the header) anyway. These two facts make it much more comparable to a conversation in a public space, which carries no expectation of privacy and thusly no law against eavesdropping.
> postcards and unencrypted radio transmissions (like say 2.4 ghz or 900 mhz cordless phones, and fm & am radio) do not carry such an expectation, so it is not illegal to snoop such traffic
As to cell phone transmissions, yes, it is illegal to eavesdrop on them. This was true before they were digital -- when anyone with a suitable receiver could tune them in. It's just as illegal now, as well as being more difficult to eavesdrop because the entire system is now digital.
yes, but a major part of the reason that it is illegal to eavesdrop on them is because they are encrypted.
Generally speaking, it is not illegal to eavesdrop on unencrypted radio transmissions, but it is illegal to eavesdrop on any encrypted radio transmission (regardless of how effective the encryption is). This is because the people who crafted the law thought that an encrypted datastream was enough of a warning to potential eavesdroppers that the datastream is intended to be private. The crime isn't breaking the encryption, but violating a reasonable assumption of privacy.
The examples I cited all broadcast unencrypted datastreams, which is why it's legal to tune into them regardless of whether you are the intended recipient.
postcards and unencrypted radio transmissions (like say 2.4 ghz or 900 mhz cordless phones, and fm & am radio) do not carry such an expectation, so it is not illegal to snoop such traffic (this is one of the reasons why cable and satellite tv is encrypted (ie scrambled); were it not encrypted in some fashion, it would be legal to set up your own equipment to capture the stream and do what yoou what with it like you do with fm and am radio).
encrypting the data, like putting something in a sealed, addressed envelope, lets everyone know that the data is not intended for anyone to read and creates an expectation of privacy. the ease of decrypting data is not really relevant (eg breaking a wep protected connection carries the same legal penalties as breaking a wpa2 protected connection) because the basis for the law against reading others' mail is the violation of a privacy that the victim took steps to create (eg its almost certainly legal to read others' postcards and definitely legal to read the outside of the envelope because no steps are taken to prevent anyone other than the intended recipient from reading the message).
you could argue that there is also an expectation of privacy inherent in the relevant link (for wifi and ethernet) layers of the networking stack since the standards call for ignoring all frames not addressed to you (a host on the network), but this argument is severely weakened by the fact that frames are sent to every host connected to the network and that determining whether you should be reading a given frame requires you to read the frame (and not just part of it, because FCS is over the whole frame, not just the header) anyway. These two facts make it much more comparable to a conversation in a public space, which carries no expectation of privacy and thusly no law against eavesdropping.