feat: add kugou db decryption logic

um_crypto/kgm/src/lib.rs

@@ -1,12 +1,17 @@
 pub mod header;
+mod pc_db_decrypt;
 pub mod v2;
 pub mod v3;
 
+pub use pc_db_decrypt::decrypt_db;
+
 use crate::header::Header;
 use crate::v2::DecipherV2;
 use crate::v3::DecipherV3;
 use thiserror::Error;
 
+use block_padding::UnpadError;
+
 #[derive(Debug, Error)]
 pub enum KugouError {
     #[error("Header too small, need at least {0} bytes.")]
@@ -23,6 +28,18 @@ pub enum KugouError {
 
     #[error("Unsupported cipher (self-test failed)")]
     SelfTestFailed,
+
+    #[error("Failed decrypt kugou db data: {0}")]
+    DecryptKugouDbError(UnpadError),
+
+    #[error("Invalid database size: {0}")]
+    InvalidDatabaseSize(usize),
+
+    #[error("Failed to decrypt page 1 (invalid header)")]
+    DecryptPage1Failed,
+
+    #[error("Database does not seem valid")]
+    InvalidPage1Header,
 }
 
 pub enum Decipher {