I want to reverse engineer an android game, found a method
public static byte[] MNNOPKMJMFP(byte[] AFFEPNLBIIC, byte[] OENOGNMAMPO, byte[] GLLEHJKGIBK) { }
Names are obfuscated, i know that this is a cryptographic function that takes three arguments - an array of bytes, key and initialization vector, i want to get their specific values, for example, an 256 bit AES key, these are dynamic objects so they have a pointer and they are in heap, this is the code from radare2 disassembler
fcn.00c63d2c ();
│ ; var int32_t var_24h @ fp-0x24
│ 0x00c63d2c f04f2de9 push {r4, r5, r6, r7, r8, sb, sl, fp, lr}
│ 0x00c63d30 1cb08de2 add fp, sp, 0x1c
│ 0x00c63d34 0cd04de2 sub sp, sp, 0xc
│ 0x00c63d38 0080a0e1 mov r8, r0
│ 0x00c63d3c d0029fe5 ldr r0, [0x00c64014] ; [0xc64014:4]=0x18f53fc
│ 0x00c63d40 0260a0e1 mov r6, r2
│ 0x00c63d44 0170a0e1 mov r7, r1
│ 0x00c63d48 00008fe0 add r0, pc, r0
│ 0x00c63d4c 0000d0e5 ldrb r0, [r0]
│ 0x00c63d50 000050e3 cmp r0, 0
│ ┌─< 0x00c63d54 0600001a bne 0xc63d74
│ │ 0x00c63d58 b8029fe5 ldr r0, [0x00c64018] ; [0xc64018:4]=0x1884b04
│ │ 0x00c63d5c 00009fe7 ldr r0, [0x00c63d64] ; [0xc63d64:4]=0xebdc4331
│ │ 0x00c63d60 000090e5 ldr r0, [r0]
│ │ ; DATA XREF from fcn.00c63d2c @ 0xc63d5c(r)
│ │ 0x00c63d64 3143dceb bl 0x374a30
│ │ 0x00c63d68 ac029fe5 ldr r0, [0x00c6401c] ; [0xc6401c:4]=0x18f53d4
│ │ 0x00c63d6c 0110a0e3 mov r1, 1
│ │ 0x00c63d70 0010cfe7 strb r1, [0x00c63d78]
│ └─> 0x00c63d74 a4029fe5 ldr r0, [0x00c64020] ; [0xc64020:4]=0x186d7dc
│ 0x00c63d78 08504de2 sub r5, sp, 8
│ 0x00c63d7c 00009fe7 ldr r0, [0x00c63d84] ; [0xc63d84:4]=0xe5900000
│ 0x00c63d80 05d0a0e1 mov sp, r5
│ ; DATA XREF from fcn.00c63d2c @ 0xc63d7c(r)
│ 0x00c63d84 000090e5 ldr r0, [r0]
│ 0x00c63d88 bf10d0e5 ldrb r1, [r0, 0xbf]
│ 0x00c63d8c 020011e3 tst r1, 2
│ ┌─< 0x00c63d90 0300000a beq 0xc63da4
│ │ 0x00c63d94 701090e5 ldr r1, [r0, 0x70]
│ │ 0x00c63d98 000051e3 cmp r1, 0
│ ┌──< 0x00c63d9c 0000001a bne 0xc63da4
│ ││ 0x00c63da0 197fdceb bl 0x383a0c
│ └└─> 0x00c63da4 0000a0e3 mov r0, 0
│ 0x00c63da8 baa1eceb bl 0x78c498
│ 0x00c63dac 0040a0e1 mov r4, r0
│ 0x00c63db0 000054e3 cmp r4, 0
│ 0x00c63db4 24500be5 str r5, [var_24h] ; 0x24
│ ┌─< 0x00c63db8 0100001a bne 0xc63dc4
│ │ 0x00c63dbc 0000a0e3 mov r0, 0
│ │ 0x00c63dc0 7cfddceb bl 0x3a33b8
│ └─> 0x00c63dc4 000094e5 ldr r0, [r4]
│ 0x00c63dc8 283190e5 ldr r3, [r0, 0x128]
│ 0x00c63dcc 2c2190e5 ldr r2, [r0, 0x12c]
│ 0x00c63dd0 0400a0e1 mov r0, r4
│ 0x00c63dd4 0710a0e1 mov r1, r7
│ 0x00c63dd8 33ff2fe1 blx r3
│ 0x00c63ddc 000094e5 ldr r0, [r4]
│ 0x00c63de0 183190e5 ldr r3, [r0, 0x118]
│ 0x00c63de4 1c2190e5 ldr r2, [r0, 0x11c]
│ 0x00c63de8 0400a0e1 mov r0, r4
│ 0x00c63dec 0610a0e1 mov r1, r6
│ 0x00c63df0 33ff2fe1 blx r3
│ 0x00c63df4 000094e5 ldr r0, [r4]
│ 0x00c63df8 241190e5 ldr r1, [r0, 0x124]
│ 0x00c63dfc 202190e5 ldr r2, [r0, 0x120]
│ 0x00c63e00 0400a0e1 mov r0, r4
│ 0x00c63e04 32ff2fe1 blx r2
│ 0x00c63e08 0060a0e1 mov r6, r0
│ 0x00c63e0c 000094e5 ldr r0, [r4]
│ 0x00c63e10 102190e5 ldr r2, [r0, 0x110]
│ 0x00c63e14 141190e5 ldr r1, [r0, 0x114]
│ 0x00c63e18 0400a0e1 mov r0, r4
│ 0x00c63e1c 32ff2fe1 blx r2
│ 0x00c63e20 0020a0e1 mov r2, r0
│ 0x00c63e24 000094e5 ldr r0, [r4]
│ 0x00c63e28 887190e5 ldr r7, [r0, 0x188]
- what did i understand from this?
- r0: used to work with pointers,
- r1, r2, r3 - used to pass arguments and temporary values,
- r4-r8 - used as temporary registers and, possibly, for storing pointers,
- sb, sl, fp - used to save stack frame's state and set it,
Addresses used as pointers
[0x00c64014], [0x00c64018], [0x00c6401c], [0x00c64020]are loaded into register r0 and used to access data in memory[r0]is a pointer that the function operates in several places, Also, will i be able to find the answer to my question in addresses offset from [r0] or not? for example[r0, 0xbf], [r0, 0x70], [r0, 0x128], [r0, 0x12c], [r0, 0x118], [r0, 0x11c], [r0, 0x124], [r0, 0x120], [r0, 0x110], [r0, 0x114], [r0, 0x188], Also this is the method (pattern for building other functions), will xrefs analysis help? Will be thankful for any tip!
