Iran GPS Spoofing and the RSA Cipher

John Young cryptome at
Thu Dec 22 22:17:19 GMT 2011

The article source responds:


PRNG means Pseudo-Random Number Generator.  Other sources that discuss 
GPS say simply "RNG".  Another way of being equally ambiguous would be to
it a "keystream."

Any cryptosystem can be used as a source PRNG.  The PRNG for M-code GPS 
is RSA, tell this cryptographer that.  RSA is the RNG keystream, GPS data
is the 
plaintext, and the M code signal is the ciphertext.  To turn the M code
into GPS plaintext you need to replicate independently the same RNG sequence 
used by the satellite to derive the GPS plaintext, to do this you use RSA
in either 
symmetric or asymmetric mode (as per red-key or black-key M-code modes, 



At 09:04 PM 12/22/2011 +0000, you wrote:
>I do wish people would check their facts sometimes. The linked article  
>asserts that "GPS (M-code) is protected against spoofing by the RSA  
>cipher" - it is not, it's protected by a keyed PRNG. You don't have to  
>be an ace cryptologist to figure this out, you just need to look up  
>"GPS signal" on Wikipedia.
>On 22 Dec 2011, at 16:33, John Young wrote:
>> Iran GPS Spoofing and the RSA Cipher

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