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Implement Telegram protocol safety checks

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This commit is contained in:
Wizou 2021-08-20 02:13:58 +02:00
parent e205244cf7
commit f2a1dbc20d
6 changed files with 87 additions and 24 deletions
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16
src/Encryption.cs
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@ -129,6 +129,7 @@ namespace WTelegram
RNG.GetBytes(bData);
var b = BigEndianInteger(bData);
var g_b = BigInteger.ModPow(serverDHinnerData.g, b, dh_prime);
ValidityChecksDH(g_a, g_b, dh_prime);
var clientDHinnerData = new ClientDHInnerData
{
nonce = nonce,
@ -193,7 +194,7 @@ namespace WTelegram
private static void ValidityChecks(BigInteger p, int g)
{
//TODO: check whether p is a safe prime (meaning that both p and (p - 1) / 2 are prime)
Helpers.Log(2, "Verifying encryption key safety... (this happens only during session negociation)");
// check that 2^2047 <= p < 2^2048
if (p.GetBitLength() != 2048) throw new ApplicationException("p is not 2048-bit number");
// check that g generates a cyclic subgroup of prime order (p - 1) / 2, i.e. is a quadratic residue mod p.
@ -209,8 +210,19 @@ namespace WTelegram
_ => true,
})
throw new ApplicationException("Bad prime mod 4g");
//TODO: check that g, g_a and g_b are greater than 1 and less than dh_prime - 1.
// check whether p is a safe prime (meaning that both p and (p - 1) / 2 are prime)
if (!p.IsProbablePrime()) throw new ApplicationException("p is not a prime number");
if (!((p - 1) / 2).IsProbablePrime()) throw new ApplicationException("(p - 1) / 2 is not a prime number");
}
private static void ValidityChecksDH(BigInteger g_a, BigInteger g_b, BigInteger dh_prime)
{
// check that g, g_a and g_b are greater than 1 and less than dh_prime - 1.
// We recommend checking that g_a and g_b are between 2^{2048-64} and dh_prime - 2^{2048-64} as well.
var l = BigInteger.One << (2048 - 64);
var r = dh_prime - l;
if (g_a < l || g_a > r || g_b < l || g_b > r)
throw new ApplicationException("g^a or g^b is not between 2^{2048-64} and dh_prime - 2^{2048-64}");
}
[TLDef(0x7A19CB76)] //RSA_public_key#7a19cb76 n:bytes e:bytes = RSAPublicKey