Merge pull request #54 from EarthCompass/master

Add EarthC's wp

Author: taoky

README.md

@@ -97,6 +97,7 @@
 | [tkmk](players/tkmk/) | 总排名第 9 名 | 赛博厨房（LEVEL 3 非预期） |
 | [ReinWD](https://github.com/ReinWD/hackergame2021_writeup/blob/main/writeup.md) | 总排名 560 | 签到，进制十六——参上，去吧！追寻自由的电波，猫咪问答 Pro Max，赛博厨房（LEVEL 0、LEVEL 1、LEVEL2） |
 | [tl2cents](players/tl2cents/README.md)  [博客](https://tl2cents.github.io/2021/10/31/Hackgame2021/) | 总排名第 70 | FLAG 助力大红包，图之上的信息，Easy RSA，马赛克，Minecraft，超 OI 的 Writeup 模拟器（前两问） |
+| [EarthC](players/EarthC/) | 总排名第 26 名 | 灯，等灯等灯, 超 OI 的 Writeup 模拟器(部分) |
 
 ## 其他资源
 

players/EarthC/README.md

@@ -0,0 +1,185 @@
+# HackerGame 2021 WP
+
+By [EarthC](https://github.com/EarthCompass)
+
+## 灯，等灯等灯
+
+### Level 0
+
+GF(256) 上面解方程即可
+
+### Level 1 / Level 2
+
+一开始还在想怎么线性规划（？），后来突然意识到，这道题目跟[LWE](https://en.wikipedia.org/wiki/Learning_with_errors)不是一样一样的吗？
+
+原题就成了一个GF(256)上的LWE问题，构造格求解CVP，代码参考https://gist.github.com/hakatashi/2266a5df35cc79de50b86d2419b33a6f
+
+这里放一个解Level 2的代码, Level 1算法完全一致，只需要换一下数据。
+
+```python
+blacklist = [(2,2),(3,2),(4,2),(4,3),(2,4),(3,4),(4,4),(4,7),(4,8),(3,8),(2,8),(2,9),(7,2),(7,3),(7,4),(8,3),(9,3),(7,7),(7,8),(7,9),(8,7),(9,7),(9,8),(9,9)]
+clicks = []
+mmap = [0]*144
+for i in range(12):
+    for j in range(12):
+        if (i,j) not in blacklist:
+            tmp = var(f'x_{i}_{j}')
+            clicks.append(tmp)
+            mmap[12*i+j] = tmp
+
+def get_click(x,y):
+    if x>=0 and x<12 and y>=0 and y < 12 and (x,y) not in blacklist:
+        return mmap[12*x+y]
+    else:
+        return 0
+
+ftarget = [189,189,189,189,189,33,33,33,189,189,189,189,189,189,189,33,33,33,189,33,44,189,189,189,189,189,189,189,189,33,33,33,33,189,189,189,189,189,189,189,189,33,189,33,33,189,189,189,189,189,189,33,33,189,189,33,33,33,189,189,189,134,33,33,189,189,189,189,33,33,189,189,189,144,33,33,189,189,189,189,33,189,189,189,189,142,33,33,189,189,189,189,33,33,33,189,189,100,142,33,189,189,189,189,33,33,33,189,189,142,142,189,189,189,189,189,189,33,189,189,189,59,142,33,189,189,189,189,33,189,189,189,189,189,33,33,189,189,189,189,189,189,189,189]
+mm = []
+for i in range(12):
+    for j in range(12):
+        data = 0
+        data += 31*get_click(i,j)
+        data += 63*get_click(i-1,j)
+        data += 63*get_click(i+1,j)
+        data += 63*get_click(i,j-1)
+        data += 63*get_click(i,j+1)
+        
+        data += 63*get_click(i+1,j+1)
+        data += 63*get_click(i+1,j-1)
+        data += 63*get_click(i-1,j+1)
+        data += 63*get_click(i-1,j-1)
+        
+        data += 127*get_click(i-2,j-2)
+        data += 127*get_click(i-2,j-1)
+        data += 127*get_click(i-2,j)
+        data += 127*get_click(i-2,j+1)
+        data += 127*get_click(i-2,j+2)
+        data += 127*get_click(i-1,j+2)
+        data += 127*get_click(i,j+2)
+        data += 127*get_click(i+1,j+2)
+        data += 127*get_click(i+2,j+2)
+        data += 127*get_click(i+2,j+1)
+        data += 127*get_click(i+2,j)
+        data += 127*get_click(i+2,j-1)
+        data += 127*get_click(i+2,j-2)
+        data += 127*get_click(i+1,j-2)
+        data += 127*get_click(i,j-2)
+        data += 127*get_click(i-1,j-2)
+        
+        coeff = []
+        for c in clicks:
+            coeff.append(data.coefficient(c))
+        mm.append(coeff)
+from sage.modules.free_module_integer import IntegerLattice
+
+# Babai's Nearest Plane algorithm
+# from: http://mslc.ctf.su/wp/plaidctf-2016-sexec-crypto-300/
+def Babai_closest_vector(M, G, target):
+    small = target
+    for _ in range(1):
+        for i in reversed(range(M.nrows())):
+            c = ((small * G[i]) / (G[i] * G[i])).round()
+            small -= M[i] * c
+    return target - small
+
+n = 144-len(blacklist)
+m = 144
+q = 256
+
+b_values = ftarget
+A_values = mm
+
+A = matrix(ZZ, m + n, m)
+for i in range(m):
+    A[i, i] = q
+for x in range(m):
+    for y in range(n):
+        A[m + y, x] = A_values[x][y]
+lattice = IntegerLattice(A, lll_reduce=True)
+print("LLL done")
+gram = lattice.reduced_basis.gram_schmidt()[0]
+target = vector(ZZ, b_values)
+res = Babai_closest_vector(lattice.reduced_basis, gram, target)
+print("Closest Vector: {}".format(res))
+
+R = IntegerModRing(q)
+M = Matrix(R, A_values)
+ingredients = M.solve_right(res)
+
+print("Ingredients: {}".format(ingredients))
+print("ok")
+cnt = 0
+ans = mmap.copy()
+for i in range(144):
+    if ans[i] != 0:
+        ans[i] = ingredients[cnt]
+        cnt+=1
+print(ans)
+        
+```
+
+## 超 OI 的 Writeup 模拟器
+
+### 果然还是逆向比较简单 / 这次没人两小时手做吧
+
+angr全自动
+
+```python
+def solve(level):
+	p = angr.Project(f'challs/{level}.bin',auto_load_libs=False)
+
+	cfg = p.analyses.CFGFast()
+	print(p)
+
+	target_addr = 0
+	for addr,b in cfg.kb.functions.items():
+		if b.returning and len(list(b.blocks)) == 2 and b.has_return:
+			print("*"*30)
+
+			target_addr = addr
+
+	a = claripy.BVS('r0',64)
+	b = claripy.BVS('r1',64)
+	add_opt = {
+		# angr.options.ZERO_FILL_UNCONSTRAINED_REGISTERS,
+		# angr.options.ZERO_FILL_UNCONSTRAINED_MEMORY,
+		# angr.options.LAZY_SOLVES,
+		# angr.options.UNICORN,
+		# angr.options.DOWNSIZE_Z3,
+		# angr.options.SIMPLIFY_CONSTRAINTS
+	}
+	rm_opt = {
+		angr.options.SIMPLIFY_MEMORY_WRITES,
+		angr.options.SIMPLIFY_REGISTER_WRITES,
+	}
+	state = p.factory.call_state(target_addr,a,b,add_options=add_opt,remove_options=rm_opt)
+
+
+	simgr = p.factory.simgr(state)
+	start_time = time.time()
+	simgr.explore(find=target_addr+33)
+	print(f"Done in {time.time()-start_time}")
+
+	end = simgr.found[0]
+
+	print("Solving。。")
+	try:
+		s = b''
+		s+=end.solver.eval(a).to_bytes(8,byteorder='little')
+		s+=end.solver.eval(b).to_bytes(8,byteorder='little')
+
+		print(level,s.decode())
+
+	except Exception as e:
+		print("error",level)
+		print(e)
+```
+
+### 什么叫无情的逆向机器
+
+angr的默认选项会在执行途中尝试化简表达式，导致大部分样本执行时间爆炸，可以手动关闭相关选项加速符号执行（虽然表达式会巨复杂）。
+
+但是z3只能解出少部分题目，剩下的大多数bin会unsat无解。
+
+过于复杂求解卡住还可以理解，但是不知道为啥会unsat，希望大佬教教。
+