Implement item table encryption

2018-07-08 16:38:45 -04:00
parent bc2d9d95a5
commit 14783a12e0
11 changed files with 214 additions and 68 deletions
--- a/decryption.asm
+++ b/decryption.asm
@@ -0,0 +1,93 @@
+
+!CryptoBuffer = "$7F5100"
+;!keyBase = "$7F50D0"
+
+;--------------------------------------------------------------------------------
+LoadStaticDecryptionKey:
+	PHB : PHA : PHX : PHY : PHP
+	REP #$30 ; set 16-bit accumulator & index registers
+	LDX.w #StaticDecryptionKey  ; Source
+	LDY.w #!keyBase             ; Target
+	LDA.w #$000F                ; Length
+	MVN $307F
+
+	PLP : PLY : PLX : PLA : PLB
+RTL
+;--------------------------------------------------------------------------------
+
+;--------------------------------------------------------------------------------
+RetrieveValueFromEncryptedTable:
+;Requires 16-bit A and X/Y
+;$00-$02 are long address of start of table
+;A is desired byte offset into table
+;Returns result in A
+	PHX : PHY
+		PHA
+			LDY $04 : PHY : LDY $06 : PHY : LDY $08 : PHY
+			LDY $0A : PHY : LDY $0C : PHY : LDY $0E : PHY
+
+				AND.w #$FFF8 : TAY
+				LDA [$00], Y : STA.l !CryptoBuffer : INY #2
+				LDA [$00], Y : STA.l !CryptoBuffer+2 : INY #2
+				LDA [$00], Y : STA.l !CryptoBuffer+4 : INY #2
+				LDA [$00], Y : STA.l !CryptoBuffer+6
+
+				; TODO: copy key into crypto Memory
+
+				LDA.w #$0002 : STA $04 ;set block size
+
+				JSL.l XXTEA_Decode
+
+			PLA : STA $0E : PLA : STA $0C : PLA : STA $0A
+			PLA : STA $08 : PLA : STA $06 : PLA : STA $04
+		PLA : AND.w #$0007 : TAX
+		LDA.l !CryptoBuffer, X
+
+		STZ.l !CryptoBuffer
+		STZ.l !CryptoBuffer+2
+		STZ.l !CryptoBuffer+4
+		STZ.l !CryptoBuffer+6
+
+	PLY : PLX
+RTL
+;--------------------------------------------------------------------------------
+
+!ChestData = "$01E96C"
+!ChestData_Payload = "$1EABC" ; !ChestData+$0150
+
+;--------------------------------------------------------------------------------
+GetChestData:
+	LDA.l IsEncrypted : BNE .encrypted
+		INC $0E : LDX.w #$FFFD ; what we wrote over
+JML.l Dungeon_OpenKeyedObject_nextChest
+
+.encrypted
+		INC $0E : LDX.w #$FFFE
+
+	.nextChest
+
+	INX #2 : CPX.w #$0150 : BEQ .couldntFindChest
+	LDA !ChestData, X : AND.w #$7FFF : CMP $A0 : BNE .nextChest
+
+	DEC $0E : BNE .nextChest
+
+	LDA $00 : PHA : LDA $02 : PHA
+
+		LDA.w #!ChestData_Payload : STA $00
+		LDA.w #!ChestData_Payload>>16 : STA $02
+
+		TXA : LSR
+		JSL RetrieveValueFromEncryptedTable
+		STA $0C
+
+	PLA : STA $02 : PLA : STA $00
+
+	LDA !ChestData, X : ASL A : BCC .smallChest
+
+JML.l Dungeon_OpenKeyedObject_bigChest ;(bank01.asm line #13783)
+
+.smallChest
+JML.l Dungeon_OpenKeyedObject_smallChest
+.couldntFindChest
+JML.l Dungeon_OpenKeyedObject_couldntFindChest
+;--------------------------------------------------------------------------------