Must check received Diffie-Hellman ephemeral in MTProto about tgl HOT 3 CLOSED

I haven't actually tried to pass 1 or p-1 as key, but believe that there is code that seems to check that 2^{2048-64} <= KEY <= p - 2^{2048-64}, which also means that the key is between 1 <= KEY <= p - 1.

https://github.com/vysheng/tgl/blob/master/mtproto-utils.c#L75-L80

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Thanks for the response. I'll look again.

Best,
Karthik

On 10 Nov 2015, at 20:33, mj [email protected] wrote:

I haven't actually tried to pass 1 or p-1 as key, but believe that there is code that seems to check that 2^{2048-64} <= KEY <= p - 2^{2048-64}, which also means that the key is between 1 <= KEY <= p - 1.

https://github.com/vysheng/tgl/blob/master/mtproto-utils.c#L75-L80 https://github.com/vysheng/tgl/blob/master/mtproto-utils.c#L75-L80
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Thanks for the response. It looks like this code checks: 2^{2048-64} <= KEY <= 2^{2048}, which is not related to $p$.
If p is also in this range, the code would certainly allow $p-1$ and probably also $p$ and $p+1$ (essentially 0,1,-1 mod p)

Yeah but it checks exactly this a few lines below https://github.com/vysheng/tgl/blob/master/mtproto-utils.c#L85-L90

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