check a for 0 in Legendre

PurpleI2P · Dec 10, 2019 · d7b8192 · d7b8192
1 parent 7417867
commit d7b8192
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/libi2pd/Elligator.cpp b/libi2pd/Elligator.cpp
@@ -160,7 +160,8 @@ namespace crypto
 
 	int Elligator2::Legendre (const BIGNUM * a, BN_CTX * ctx) const
 	{
-		// assume a < p, so don't check for a % p = 0
+		// assume a < p, so don't check for a % p = 0, but a = 0 only
+		if (BN_is_zero(a)) return 0; 
 		BIGNUM * r = BN_CTX_get (ctx);
 		BN_mod_exp (r, a, p12, p, ctx); // 	r = a^((p-1)/2) mod p
 		if (BN_is_word(r, 1))