CTF WriteUps
Bakeware
- Category: reverse
- Difficulty: medium-hard
- Author: Quack
Grandma had her secret family recipe stolen! All she has left now is a weird and rusty file. Please figure out what happened to the recipe, so we can get back to baking!
Solution:
- Run diec on the binary
$ diec rev_bakeware/Bakeware
ELF64
Compiler: Rust
Compiler: GCC(3.X)
Library: GLIBC(2.34)[DYN AMD64-64]
The binary is compile with Rust however the main caveat of reversing a rust binary is that its heavy use of inling,monomorphiszation and complex abstractions which produces bloated and compiler-optimized machine code that slightly obscures the original program logic.
- Disassemble the binary
At the address 00408c60, there is main function of Bakeware::main.
00408c60 int64_t Bakeware::main::h837f6b7d44b9b487()
00408c60 {
00408c60 uint64_t var_7d8 = 0x1b600000000;
00408c83 int32_t var_7d0 = 0;
00408c8e int16_t var_7cc = 0;
00408c98 (uint8_t)var_7d0 = 1;
00408cbc int32_t var_408;
00408cbc std::fs::OpenOptions::_open::hce0f5e8979d4b5a1(&var_408, &var_7d8,
00408cbc "Grandmas_Secret_Baking_Family_Recipe.txtFile not found. Nothing to steal :(\n"
00408cbc "502ff05a7b51b76e740b19cc4957ad118897a25becbb87fcb662a14b2e56a5d9Secret recipe not "
00408cbc "found. Nothing to steal :(\nGrandmas_Secret_Baking_Family_Recipe",
00408cbc 0x28);
00408cbc
00408cca if (var_408 == 1)
00408cca {
0040987a var_7d8 = &data_45fc18;
00409882 var_7d0 = 1;
0040988e int64_t var_7c8_7 = 8;
0040989d int128_t var_7c0_3 = {0};
004098ad std::io::stdio::_print::h2bb3f89bb77308e4(&var_7d8);
004098b5 std::process::exit::hc9c70ab8de590b08(0);
004098b5 /* no return */
00408cca }
00408cca
00408cd7 int32_t fd_1;
00408cd7 int32_t fd = fd_1;
00408cdb var_408 = 0;
00408ce7 char* var_400 = 1;
00408cf3 uint64_t var_3f8 = 0;
00408d0c char rax_1;
00408d0c uint64_t rdx;
00408d0c rax_1 =
00408d0c _$LT$std..fs..File$u20$a...T$::read_to_string::h4d12b8c695679e1f(&fd, &var_408);
00408d0c
00408d14 if (rax_1 & 1)
00408d14 {
004098c0 var_7d8 = rdx;
004098ea core::result::unwrap_failed::h1b5ed8541c7bebd6(
004098ea "called `Result::unwrap()` on an `Err` value/home/quack/."
004098ea "rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/slice."
004098ea "rsPadErrorextern "Oh! A Good Old Hello World Binary That Is Totally Innocent "
004098ea "And Does Not St",
004098ea 0x2b, &var_7d8);
004098ea /* no return */
00408d14 }
00408d14
00408d2a _$LT$$RF$alloc..string.....Digest$GT$::digest::hac6b4adf5efc5232(&var_7d8,
00408d2a &var_408);
00408d30 int64_t rax_2 = var_408;
00408d55 uint64_t rax_4 = var_7d8;
00408d62 int64_t r14 = var_7d0;
00408d76 close(fd);
00408d80 int64_t var_968 = r14;
00408d84 int64_t var_7c8;
00408d84
00408d84 if (var_7c8 == 0x40 && !bcmp(r14,
00408d84 "502ff05a7b51b76e740b19cc4957ad118897a25becbb87fcb662a14b2e56a5d9Secret recipe not "
00408d84 "found. Nothing to steal :(\nGrandmas_Secret_Baking_Family_Recipe",
00408d84 0x40))
00408d84 {
00408db6 uint64_t var_820;
00408db6 Bakeware::get_key_part::hd4d7de7168456fd6(&var_820);
00408dcd uint64_t var_808;
00408dcd Bakeware::get_key_part::hd4d7de7168456fd6(&var_808);
00408de4 uint64_t var_7f0;
00408de4 Bakeware::get_key_part::hd4d7de7168456fd6(&var_7f0);
00408dfb int64_t var_8d8;
00408dfb Bakeware::get_key_part::hd4d7de7168456fd6(&var_8d8);
00408e12 uint64_t var_878;
00408e12 Bakeware::get_key_part::hd4d7de7168456fd6(&var_878);
00408e29 uint64_t var_860;
00408e29 Bakeware::get_key_part::hd4d7de7168456fd6(&var_860);
00408e3d int32_t* var_918;
00408e3d Bakeware::get_key_part::hd4d7de7168456fd6(&var_918);
00408e51 Bakeware::get_key_part::hd4d7de7168456fd6(&fd);
00408e61 uint64_t var_810;
00408e61 int64_t r14_1;
00408e61
00408e61 if (var_810 < 0)
004098f5 r14_1 = 0;
00408e61 else
00408e61 {
00408e6f int64_t rax_7;
00408e6f
00408e6f if (!var_810)
00408e6f {
00408e99 rax_7 = 1;
00408ebf label_408ebf:
00408ebf int64_t var_818;
00408ebf memcpy(rax_7, var_818, var_810);
00408ec5 uint64_t rax_8 = var_808;
00408ee2 uint64_t rax_10 = var_7f0;
00408eff uint64_t rax_12 = var_820;
00408f0c int64_t rax_13 = var_8d8;
00408f2c uint64_t rax_15 = var_878;
00408f49 uint64_t rax_17 = var_860;
00408f66 int32_t* rax_19 = var_918;
00408f85 uint64_t var_948;
00408f85 int64_t var_8c0_1;
00408f85
00408f85 if (var_948 < 0)
00409910 var_8c0_1 = 0;
00408f85 else
00408f85 {
00408fdd int64_t r15_1;
00408fdd
00408fdd if (!var_948)
00408fdd {
00409012 r15_1 = 1;
00409021 label_409021:
00409021 int64_t var_950;
00409021 memcpy(r15_1, var_950, var_948);
0040902c uint64_t var_6f0 = var_948;
00409034 int128_t zmm0 = fd;
00409041 var_7d8 = var_810;
00409051 var_7d0 = rax_7;
00409059 uint64_t var_7c8_1 = var_810;
00409066 int128_t var_7c0;
00409066 (uint64_t)var_7c0 = rax_8;
00409076 int64_t var_800;
00409076 *(uint64_t*)((char*)var_7c0)[8] = var_800;
0040907e int64_t var_7f8;
0040907e int64_t var_7b0 = var_7f8;
004090a3 int64_t var_7e0;
004090a3 int64_t var_798 = var_7e0;
004090c8 uint64_t var_780 = var_810;
004090f8 int64_t var_8c8;
004090f8 int64_t var_768 = var_8c8;
00409125 int64_t var_868;
00409125 int64_t var_750 = var_868;
00409152 int64_t var_850;
00409152 int64_t var_738 = var_850;
0040917f int64_t var_908;
0040917f int64_t var_720 = var_908;
00409197 uint64_t var_708 = var_948;
004091b4 _$LT$$u5b$V$u5d$$u20$as$...$T$GT$$GT$::concat::hb51e64af983ca0d5(
004091b4 &var_408, &var_7d8, 0xa);
004091b4
004091d0 if (var_7d8)
004091df __rust_dealloc(var_7d0);
004091df
004091f0 if ((uint64_t)var_7c0)
004091ff __rust_dealloc(*(uint64_t*)((char*)var_7c0)[8]);
004091ff
00409210 int64_t var_7e8;
00409210
00409210 if (rax_10)
0040921f __rust_dealloc(var_7e8);
0040921f
00409230 if (rax_12)
0040923f __rust_dealloc(var_818);
0040923f
00409250 int64_t var_8d0;
00409250
00409250 if (rax_13)
0040925f __rust_dealloc(var_8d0);
00409270 int64_t var_870;
00409270
00409270 if (rax_15)
0040927f __rust_dealloc(var_870);
00409290 int64_t var_858;
00409290
00409290 if (rax_17)
0040929f __rust_dealloc(var_858);
004092b0 int64_t var_910;
004092b0
004092b0 if (rax_19)
004092bf __rust_dealloc(var_910);
004092bf
004092d0 if (var_948)
004092df __rust_dealloc(r15_1);
004092df
004092f0 if ((uint64_t)zmm0)
004092ff __rust_dealloc(*(uint64_t*)((char*)zmm0)[8]);
004092ff
00409305 int64_t rbx_2 = var_408;
00409305
00409323 if (var_3f8 != 0x20)
00409323 {
004093b4 var_7d8 = &data_45fbd8;
004093bc var_7d0 = 1;
004093c8 int64_t var_7c8_2 = 8;
004093d7 int128_t var_7c0_1 = {0};
004093ee core::panicking::panic_fmt::h896a0727a1a943f9(&var_7d8);
004093ee /* no return */
00409323 }
00409323
00409335 uint64_t var_938_1 = var_3f8 + 0x10;
0040933a int64_t rbx_3;
0040933a
0040933a if (var_3f8 + 0x10 < 0)
00409939 rbx_3 = 0;
0040933a else
0040933a {
00409347 __rust_no_alloc_shim_is_unstable;
0040934a rbx_3 = 1;
00409357 int64_t rax_48 = __rust_alloc_zeroed(var_3f8 + 0x10, 1);
00409357
00409360 if (rax_48)
00409360 {
00409377 memcpy(rax_48, var_400, var_3f8);
00409384 uint8_t aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79_1 = aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79;
00409389 uint8_t rax_50;
00409389
00409389 if (aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79_1
00409389 != 1 && (uint32_t)aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79_1
00409389 == 0xff)
004093f9 rax_50 = aes::autodetect::aes_int...it_get::init_inner::hd807519274f9a4da();
004093f9
00409401 if (aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79_1
00409401 != 1 && ((uint32_t)aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79_1
00409401 != 0xff || !rax_50))
004093a2 aes::soft::fixslice::aes256_key_schedule::hda8c6ed16e648178(
004093a2 &var_408, var_400);
00409401 else
00409401 {
00409410 _$LT$aes..ni..Aes256Enc$.....KeyInit$GT$::new::haaa3a7e26e4efd28(
00409410 &var_408, var_400);
00409429 aes::ni::aes256::inv_exp...cfbcbfed022f.llvm.3969909835275325008();
00409448 memcpy(&var_7d8, &var_408, 0xf0);
0040945b memcpy(&var_408, &var_7d8, 0x1e0);
00409401 }
00409401
0040947d memcpy(&var_7d8, &var_408, 0x3c0);
00409487 int128_t var_418;
00409487 __builtin_strncpy(&var_418, "1234567890123456", 0x10);
0040949f memcpy(&var_408, &var_7d8, 0x3d0);
004094a5 uint64_t r14_5 = var_3f8 >> 4;
004094b6 uint64_t r13_3 = (uint64_t)(uint32_t)var_3f8 & 0xf;
004094bd fd = {0};
004094c2 int64_t r15_3 = rax_48 + (0x7ffffffffffffff0 & var_3f8);
004094d0 memcpy(&fd, r15_3, r13_3);
004094eb memset(&var_968 + r13_3 + 0x10,
004094eb (uint32_t)(0x10 - (uint8_t)r13_3), 0x10 - r13_3);
004094f6 var_7d8 = fd;
004094fe int64_t var_7c8_3 = rax_48;
00409506 (uint64_t)var_7c0 = rax_48;
0040950e *(uint64_t*)((char*)var_7c0)[8] = r14_5;
00409526 void var_48;
00409526 fd = &var_48;
0040952b int64_t var_950_1 = rax_48;
00409530 int64_t var_948_1 = rax_48;
00409535 uint64_t var_940 = r14_5;
00409547 _$LT$Alg$u20$as$u20$ciph...t_with_backend_mut::hd6fdacc991ffc37b(
00409547 &var_408, &fd);
0040954c fd = &var_48;
00409551 uint64_t* var_950_2 = &var_7d8;
00409556 int64_t var_948_2 = r15_3;
0040956b _$LT$Alg$u20$as$u20$ciph...t_with_backend_mut::h9dfecfe6a3f33a05(
0040956b &var_408, &fd);
00409570 int64_t r14_6 = (uint64_t)var_7c0;
00409594 aes::autodetect::aes_intrinsics::STORAGE::hc8673b1237a96b79;
00409594
0040959a if (!r14_6)
0040959a {
00409980 core::result::unwrap_failed::h1b5ed8541c7bebd6(
00409980 "called `Result::unwrap()` on an `Err` "
00409980 "value/home/quack/."
00409980 "rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/slice."
00409980 "rsPadErrorextern "Oh! A Good Old Hello World Binary "
00409980 "That Is Totally Innocent And Does Not St",
00409980 0x2b, &var_7d8);
00409980 /* no return */
0040959a }
0040959a
004095a0 int64_t r13_6 =
004095a0 (*(uint64_t*)((char*)var_7c0)[8] + 1) << 4;
004095a7 int64_t rbx_4;
004095a7
004095a7 if (r13_6 < 0)
0040998b rbx_4 = 0;
004095a7 else
004095a7 {
004095ad void* r15_4;
004095ad
004095ad if (!r13_6)
004095ad {
004095da r15_4 = 1;
004095e9 label_4095e9:
004095e9 memcpy(r15_4, r14_6, r13_6);
004095fc __rust_dealloc(rax_48);
004095fc
0040960a if (rbx_2)
00409616 __rust_dealloc(var_400);
00409616
00409627 if (rax_2)
00409633 __rust_dealloc(var_400);
00409633
00409640 var_860 =
00409640 "Grandmas_Secret_Baking_Family_Recipe";
00409648 int64_t var_858_1 = 0x24;
0040965c fd = &var_860;
00409668 char* var_950_3 = _$LT$$RF$T$u20$as$u20$co.....Display$GT$::fmt::h36fbadcb1601d653;
00409674 var_7d8 = &data_45fb38;
0040967c var_7d0 = 2;
00409688 *(uint64_t*)((char*)var_7c0)[8] = 0;
00409694 int32_t* var_7c8_4 = &fd;
0040969c (uint64_t)var_7c0 = 1;
004096b8 alloc::fmt::format::format_inner::h49a3ea498526530d(
004096b8 &var_408, &var_7d8);
004096c6 fd = var_408;
004096d3 uint64_t var_948_3 = var_3f8;
004096e2 var_7d8 = 0x1b600000000;
004096ea int32_t var_7d0_1 = 0;
004096f5 int16_t var_7cc_1 = 0;
004096ff *(uint8_t*)((char*)var_7d0_1)[1] = 1;
00409707 (uint8_t)var_7cc_1 = 1;
0040970f *(uint8_t*)((char*)var_7d0_1)[3] = 1;
0040972c std::fs::OpenOptions::_open::hce0f5e8979d4b5a1(
0040972c &var_918, &var_7d8, var_950_3, var_3f8);
0040972c
00409737 if ((uint32_t)var_918 == 1)
00409737 {
004099ac var_7d8 = &data_45fb98;
004099b4 var_7d0_1 = 1;
004099c0 int64_t var_7c8_8 = 8;
004099cf int128_t var_7c0_4 = {0};
004099df std::io::stdio::_print::h2bb3f89bb77308e4(
004099df &var_7d8);
004099ea std::process::exit::hc9c70ab8de590b08(1);
004099ea /* no return */
00409737 }
00409737
00409741 (uint32_t)var_8d8 =
00409741 *(uint32_t*)((char*)var_918)[4];
00409756 char const (** rax_57)[0x128] = std::io::Write::write_all::hb7d9f4951e8a6485(
00409756 &var_8d8, r15_4, r13_6);
00409756
0040975e if (rax_57)
0040975e {
004099f2 var_878 = rax_57;
00409a02 var_918 = &var_878;
00409a0e int64_t (* var_910_2)(int64_t* arg1,
00409a0e int64_t* arg2) = _$LT$std..io..error..Err.....Display$GT$::fmt::hf3dbdd06f07e2f1c;
00409a1a var_7d8 = &data_45fb58;
00409a22 var_7d0_1 = 2;
00409a2e *(uint64_t*)((char*)var_7c0)[8] = 0;
00409a3a int32_t** var_7c8_9 = &var_918;
00409a42 (uint64_t)var_7c0 = 1;
00409a56 std::io::stdio::_print::h2bb3f89bb77308e4(
00409a56 &var_7d8);
00409a61 std::process::exit::hc9c70ab8de590b08(1);
00409a61 /* no return */
0040975e }
0040975e
00409764 var_918 = &fd;
00409770 int64_t (* var_910_1)(void* arg1,
00409770 int64_t* arg2) = _$LT$alloc..string..Stri.....Display$GT$::fmt::h018e70d5162f383e;
0040977c var_7d8 = &data_45fb78;
00409784 var_7d0_1 = 2;
00409790 *(uint64_t*)((char*)var_7c0)[8] = 0;
0040979c int32_t** var_7c8_5 = &var_918;
004097a4 (uint64_t)var_7c0 = 1;
004097b8 std::io::stdio::_print::h2bb3f89bb77308e4(
004097b8 &var_7d8);
004097c5 int64_t result = close((uint32_t)var_8d8);
004097c5
004097d3 if (fd)
004097df result = __rust_dealloc(var_950_3);
004097df
004097e8 if (r13_6)
004097f5 result = __rust_dealloc(r15_4);
004097f5
00409803 if (!rax_4)
00409825 return result;
00409825
0040980e return __rust_dealloc(var_968);
004095ad }
004095ad
004095b6 __rust_no_alloc_shim_is_unstable;
004095b9 rbx_4 = 1;
004095c6 void* rax_55 = __rust_alloc(r13_6, 1);
004095c6
004095cf if (rax_55)
004095cf {
004095d5 r15_4 = rax_55;
004095d8 goto label_4095e9;
004095cf }
004095a7 }
004095a7
0040999a alloc::raw_vec::handle_error::h2c5ced866628b5d4(rbx_4);
0040999a /* no return */
00409360 }
0040933a }
0040933a
00409953 alloc::raw_vec::handle_error::h2c5ced866628b5d4(rbx_3);
00409953 /* no return */
00408fdd }
00408fdd
00408fee var_8c0_1 = 1;
00408ffe int64_t rax_25 = __rust_alloc(var_948, 1);
00408ffe
00409007 if (rax_25)
00409007 {
0040900d r15_1 = rax_25;
00409010 goto label_409021;
00409007 }
00408f85 }
00408f85
0040992e alloc::raw_vec::handle_error::h2c5ced866628b5d4(var_8c0_1);
0040992e /* no return */
00408e6f }
00408e6f
00408e78 __rust_no_alloc_shim_is_unstable;
00408e7b r14_1 = 1;
00408e89 rax_7 = __rust_alloc(var_810, 1);
00408e89
00408e92 if (rax_7)
00408e92 goto label_408ebf;
00408e61 }
00408e61
00409905 alloc::raw_vec::handle_error::h2c5ced866628b5d4(r14_1);
00409905 /* no return */
00408d84 }
00408d84
0040982d var_7d8 = &data_45fc28;
00409835 var_7d0 = 1;
00409841 int64_t var_7c8_6 = 8;
00409850 int128_t var_7c0_2 = {0};
00409860 std::io::stdio::_print::h2bb3f89bb77308e4(&var_7d8);
00409868 std::process::exit::hc9c70ab8de590b08(0);
00409868 /* no return */
00408c60 }
- finds
Grandmas_Secret_Baking_Family_Recipe.txt - performs SHA256 hash and compares against hardcoded value:
502ff05a7b51b76e740b19cc4957ad118897a25becbb87fcb662a14b2e56a5d9, if hash doesnt match, exits with"File not found. Nothing to steal :(" - if hash matches, calls
get_key_part()function 8 times - uses assembled key for AES-256 encryption
- Bypass Hash Check
- Set breakpoint at hash comparison (0x408d84)
- Use debugger to force the conditional jump to succeed:
*0x408d84 set $eflags |= 0x40
- Key extraction analysis
- After bypass, program calls
get_key_part()function 8 times - Each call extracts bytes from two hardcoded strings containing various text
- Function uses
from_iterto process the strings and extract specific characters
- After bypass, program calls
- Find the IV
- Analyzed hardcoded strings in
get_key_partfunction - Found hex string:
12345678901234560123456789abcdefIV:12345678901234560123456789abcdefKey:OTHellOTotallyStealGoodRecipes!!
- Analyzed hardcoded strings in
- Decrypt the flag
- Using AES-256 CBC
$ openssl enc -aes-256-cbc -d \
-in Grandmas_Secret_Baking_Family_Recipe.enc \
-K $(echo -n "OTHellOTotallyStealGoodRecipes!!" | xxd -p | tr -d '\n') \
-iv 12345678901234560123456789abcdef \
-out Grandmas_Secret_Baking_Family_Recipe.dec
Flag: brunner{Gr4ndm4_sh0u1d_R34lL7_l34rn_b3tt3r_0ps3c}