Add RSA test.

td/mtproto/RSA.cpp

@@ -104,6 +104,7 @@ size_t RSA::encrypt(unsigned char *from, size_t from_len, size_t max_from_len, u
   CHECK(chunks * 256 <= to_len);
   Random::secure_bytes(from + from_len, pad);
 
+  size_t result = chunks * 256;
   BigNumContext ctx;
   BigNum y;
   while (chunks-- > 0) {
@@ -112,7 +113,7 @@ size_t RSA::encrypt(unsigned char *from, size_t from_len, size_t max_from_len, u
     MutableSlice(to, 256).copy_from(y.to_binary(256));
     to += 256;
   }
-  return chunks * 256;
+  return result;
 }
 
 void RSA::decrypt_signature(Slice from, MutableSlice to) const {

test/mtproto.cpp

@@ -711,3 +711,22 @@ TEST(Mtproto, TlsTransport) {
   }
   sched.finish();
 }
+
+TEST(Mtproto, RSA) {
+  auto pem = td::Slice(
+      "-----BEGIN RSA PUBLIC KEY-----\n"
+      "MIIBCgKCAQEAr4v4wxMDXIaMOh8bayF/NyoYdpcysn5EbjTIOZC0RkgzsRj3SGlu\n"
+      "52QSz+ysO41dQAjpFLgxPVJoOlxXokaOq827IfW0bGCm0doT5hxtedu9UCQKbE8j\n"
+      "lDOk+kWMXHPZFJKWRgKgTu9hcB3y3Vk+JFfLpq3d5ZB48B4bcwrRQnzkx5GhWOFX\n"
+      "x73ZgjO93eoQ2b/lDyXxK4B4IS+hZhjzezPZTI5upTRbs5ljlApsddsHrKk6jJNj\n"
+      "8Ygs/ps8e6ct82jLXbnndC9s8HjEvDvBPH9IPjv5JUlmHMBFZ5vFQIfbpo0u0+1P\n"
+      "n6bkEi5o7/ifoyVv2pAZTRwppTz0EuXD8QIDAQAB\n"
+      "-----END RSA PUBLIC KEY-----");
+  auto rsa = RSA::from_pem_public_key(pem).move_as_ok();
+  ASSERT_EQ(-7596991558377038078, rsa.get_fingerprint());
+  ASSERT_EQ(256u, rsa.size());
+
+  string s(255, '\0');
+  string to(256, '\0');
+  ASSERT_EQ(256u, rsa.encrypt(MutableSlice(s).ubegin(), 10, 255, MutableSlice(to).ubegin(), 256));
+}