diff --git a/adapters/src/official/game_main_config.rs b/adapters/src/official/game_main_config.rs
index 39f914e..c6096d2 100644
--- a/adapters/src/official/game_main_config.rs
+++ b/adapters/src/official/game_main_config.rs
@@ -77,8 +77,12 @@ fn parse_legacy_game_main_config(bytes: &[u8]) -> Result<YostarJpGameMainConfig,
 }
 
 fn parse_game_main_config_json(value: &str) -> Result<YostarJpGameMainConfig, String> {
-    serde_json::from_str(value)
-        .map_err(|error| format!("Failed to parse decrypted GameMainConfig JSON: {error}"))
+    let config: YostarJpGameMainConfig = serde_json::from_str(value)
+        .map_err(|error| format!("Failed to parse decrypted GameMainConfig JSON: {error}"))?;
+    if !game_main_config_has_known_field(&config) {
+        return Err("Decrypted GameMainConfig JSON did not contain any known fields".to_string());
+    }
+    Ok(config)
 }
 
 fn parse_obfuscated_game_main_config(bytes: &[u8]) -> Result<YostarJpGameMainConfig, String> {
@@ -113,6 +117,13 @@ fn parse_obfuscated_game_main_config(bytes: &[u8]) -> Result<YostarJpGameMainCon
     })
 }
 
+fn game_main_config_has_known_field(config: &YostarJpGameMainConfig) -> bool {
+    config.skip_tutorial.is_some()
+        || config.language.is_some()
+        || config.default_connection_group.is_some()
+        || config.server_info_data_url.is_some()
+}
+
 fn decrypt_inferred_ascii_json(bytes: &[u8]) -> Result<String, String> {
     if !bytes.len().is_multiple_of(2) {
         return Err("Obfuscated GameMainConfig byte length is not UTF-16LE aligned".to_string());
@@ -362,9 +373,9 @@ fn round(acc: u32, input: u32) -> u32 {
 
 fn avalanche(mut hash: u32) -> u32 {
     hash ^= hash >> 15;
-    hash = hash.wrapping_mul(0x85EB_CA6B);
+    hash = hash.wrapping_mul(0x85EB_CA77);
     hash ^= hash >> 13;
-    hash = hash.wrapping_mul(0xC2B2_AE35);
+    hash = hash.wrapping_mul(0xC2B2_AE3D);
     hash ^= hash >> 16;
     hash
 }
@@ -616,6 +627,18 @@ mod tests {
         );
     }
 
+    #[test]
+    fn rejects_legacy_json_without_known_fields() {
+        let error = parse_game_main_config_json(r#"{"unknown":"value"}"#).unwrap_err();
+
+        assert!(error.contains("did not contain any known fields"));
+    }
+
+    #[test]
+    fn uses_standard_xxhash32_seed_for_game_main_config_key() {
+        assert_eq!(xxhash32(b"GameMainConfig"), 2131083068);
+    }
+
     #[test]
     #[ignore]
     fn extracts_game_main_config_bytes_from_serialized_assets() {
diff --git a/infrastructure/src/official_download.rs b/infrastructure/src/official_download.rs
index 7fa4028..43c77ab 100644
--- a/infrastructure/src/official_download.rs
+++ b/infrastructure/src/official_download.rs
@@ -1684,9 +1684,9 @@ fn xxhash32_round(acc: u32, input: u32) -> u32 {
 
 fn xxhash32_avalanche(mut hash: u32) -> u32 {
     hash ^= hash >> 15;
-    hash = hash.wrapping_mul(0x85EB_CA6B);
+    hash = hash.wrapping_mul(0x85EB_CA77);
     hash ^= hash >> 13;
-    hash = hash.wrapping_mul(0xC2B2_AE35);
+    hash = hash.wrapping_mul(0xC2B2_AE3D);
     hash ^= hash >> 16;
     hash
 }
@@ -2148,8 +2148,8 @@ exit 22
             report.verified_hashes[0].algorithm,
             OfficialResourceHashAlgorithm::XxHash32Decimal
         );
-        assert_eq!(report.verified_hashes[0].expected, "3223500437");
-        assert_eq!(report.verified_hashes[0].actual, "3223500437");
+        assert_eq!(report.verified_hashes[0].expected, "2044170421");
+        assert_eq!(report.verified_hashes[0].actual, "2044170421");
 
         let manifest = service.read_download_manifest().unwrap();
         assert_eq!(manifest.version, DOWNLOAD_MANIFEST_VERSION);
@@ -2328,7 +2328,7 @@ exit 22
             let bytes = if url.ends_with("/TableBundles/TableCatalog.bytes") {
                 b"ExcelDB.db".to_vec()
             } else if url.ends_with("/TableBundles/TableCatalog.hash") {
-                b"3223500437".to_vec()
+                b"2044170421".to_vec()
             } else if url.ends_with(".zip") {
                 one_file_zip(b"fixture.txt", b"ok")
             } else {
@@ -2514,9 +2514,11 @@ exit 22
 
     #[test]
     fn verifies_known_real_seed_catalog_hash_samples() {
-        assert_eq!(xxhash32(b"ExcelDB.db"), 3223500437);
-        assert_eq!(xxhash32(b"FullPatch_000.zip"), 3628251239);
-        assert_eq!(xxhash32(b"JP_Airi_Win.zip"), 876690720);
+        assert_eq!(xxhash32(b""), 46947589);
+        assert_eq!(xxhash32(b"ExcelDB.db"), 2044170421);
+        assert_eq!(xxhash32(b"FullPatch_000.zip"), 4038880697);
+        assert_eq!(xxhash32(b"JP_Airi_Win.zip"), 1416778215);
+        assert_eq!(xxhash32(b"ExcelDB.db ExcelDB.db"), 2147704569);
     }
 
     #[test]
diff --git a/infrastructure/tests/official_game_main_config_bootstrap.rs b/infrastructure/tests/official_game_main_config_bootstrap.rs
index cbee3dd..9792315 100644
--- a/infrastructure/tests/official_game_main_config_bootstrap.rs
+++ b/infrastructure/tests/official_game_main_config_bootstrap.rs
@@ -787,9 +787,9 @@ fn round(acc: u32, input: u32) -> u32 {
 
 fn avalanche(mut hash: u32) -> u32 {
     hash ^= hash >> 15;
-    hash = hash.wrapping_mul(0x85EB_CA6B);
+    hash = hash.wrapping_mul(0x85EB_CA77);
     hash ^= hash >> 13;
-    hash = hash.wrapping_mul(0xC2B2_AE35);
+    hash = hash.wrapping_mul(0xC2B2_AE3D);
     hash ^= hash >> 16;
     hash
 }