crypto: turn impossible DH errors into assertions

PR-URL: #31934
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>

src/node_crypto.cc

@@ -5884,11 +5884,7 @@ void DiffieHellman::ComputeSecret(const FunctionCallbackInfo<Value>& args) {
 
   ClearErrorOnReturn clear_error_on_return;
 
-  if (args.Length() == 0) {
-    return THROW_ERR_MISSING_ARGS(
-        env, "Other party's public key argument is mandatory");
-  }
-
+  CHECK_EQ(args.Length(), 1);
   THROW_AND_RETURN_IF_NOT_BUFFER(env, args[0], "Other party's public key");
   ArrayBufferViewContents<unsigned char> key_buf(args[0].As<ArrayBufferView>());
   BignumPointer key(BN_bin2bn(key_buf.data(), key_buf.length(), nullptr));
@@ -5948,11 +5944,7 @@ void DiffieHellman::SetKey(const FunctionCallbackInfo<Value>& args,
 
   char errmsg[64];
 
-  if (args.Length() == 0) {
-    snprintf(errmsg, sizeof(errmsg), "%s argument is mandatory", what);
-    return THROW_ERR_MISSING_ARGS(env, errmsg);
-  }
-
+  CHECK_EQ(args.Length(), 1);
   if (!Buffer::HasInstance(args[0])) {
     snprintf(errmsg, sizeof(errmsg), "%s must be a buffer", what);
     return THROW_ERR_INVALID_ARG_TYPE(env, errmsg);