Added noisy encryption

CrewCTF2024-noisy-encryption/description.yml

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+name: Noisy encryption
+authors:
+  - KLPP
+original_ctf: 'CrewCTF 2024'
+year: 2024
+description: >-
+  I can encrypt your messages, however, I will reveal just a little bit of information ...
+base64_flag: 'Y3Jld3tEMWN0MW9uNHJ5XzR0dGFja3M/XzR0X3RoMXNfVDFtM18wZl95MzRyX0E3XzdoMTVfdGltM18wZl9kNHlfMW5fN2gxc19QNHJ0XzBmX0MwdW50cnk/fQ=='
+flag_format: 'crew{FLAG}'

CrewCTF2024-noisy-encryption/release_files/server.py

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+
+import secrets
+import sympy
+
+FLAG="crew{**REDACTED**}"
+BITS=512
+LIM=pow(2,BITS)
+
+while True:
+	while (not sympy.isprime(p:=secrets.randbelow(LIM//2)+LIM//2)) or (p-1)%3==0:
+		pass
+
+	while (not sympy.isprime(q:=secrets.randbelow(LIM//2)+LIM//2)) or (q-1)%3==0:
+		pass
+
+	n=p*q
+	if n>pow(2,1023):
+		break
+
+phi=(p-1)*(q-1)
+e=3
+Secret=secrets.randbelow(LIM)
+d=pow(e,-1,phi)
+sig=pow(Secret,d,n)
+
+print("The signature is: "+str(sig))
+
+def hamming_weight(x):
+	return sum([int(y) for y in bin(x)[2:]])
+
+
+while True:
+	print("I can encrypt anything for you! But the bits may get messy")
+	msg=input()
+	if msg=="guess":
+		print("Do you know the secret?")
+		msg=int(input())
+		if msg==Secret:
+			print("You sure do! Here is your prize:")
+			print(FLAG)
+			exit(0)
+		else:
+			print("Wrong answer!")
+			exit(0)
+	msg=int(msg)
+	enc=pow(msg,3,n)
+	print(hamming_weight(enc)%2)

CrewCTF2024-noisy-encryption/server_files/Dockerfile

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+FROM python:3.10-slim-buster
+RUN apt update -y && apt install -y xinetd && apt clean && rm -rf /var/lib/apt/lists/*
+
+RUN useradd -d /home/ctf -m ctf
+USER ctf
+
+RUN pip3 install --no-cache-dir sympy==1.13.3
+
+COPY xinetd /etc/xinetd.d/xinetd
+COPY server.py /home/ctf/server.py
+
+CMD ["/usr/sbin/xinetd", "-dontfork"]

CrewCTF2024-noisy-encryption/server_files/server.py

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+
+import secrets
+import sympy
+
+FLAG="crew{D1ct1on4ry_4ttacks?_4t_th1s_T1m3_0f_y34r_A7_7h15_tim3_0f_d4y_1n_7h1s_P4rt_0f_C0untry?}"
+BITS=512
+LIM=pow(2,BITS)
+
+while True:
+	while (not sympy.isprime(p:=secrets.randbelow(LIM//2)+LIM//2)) or (p-1)%3==0:
+		pass
+
+	while (not sympy.isprime(q:=secrets.randbelow(LIM//2)+LIM//2)) or (q-1)%3==0:
+		pass
+
+	n=p*q
+	if n>pow(2,1023):
+		break
+
+phi=(p-1)*(q-1)
+e=3
+Secret=secrets.randbelow(LIM)
+d=pow(e,-1,phi)
+sig=pow(Secret,d,n)
+
+print("The signature is: "+str(sig))
+
+def hamming_weight(x):
+	return sum([int(y) for y in bin(x)[2:]])
+
+
+while True:
+	print("I can encrypt anything for you! But the bits may get messy")
+	msg=input()
+	if msg=="guess":
+		print("Do you know the secret?")
+		msg=int(input())
+		if msg==Secret:
+			print("You sure do! Here is your prize:")
+			print(FLAG)
+			exit(0)
+		else:
+			print("Wrong answer!")
+			exit(0)
+	msg=int(msg)
+	enc=pow(msg,3,n)
+	print(hamming_weight(enc)%2)

CrewCTF2024-noisy-encryption/server_files/xinetd

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+service ctf
+{
+    disable        = no
+    type           = UNLISTED
+    wait           = no
+    server         = /usr/local/bin/python3
+    server_args    = /home/ctf/server.py
+    socket_type    = stream
+    protocol       = tcp
+    user           = ctf
+    bind           = 0.0.0.0
+    port           = 1337
+    flags          = REUSE
+    per_source	   = 2
+    rlimit_cpu	   = 30
+    log_type       = FILE /home/ctf/log
+    log_on_success = HOST PID EXIT DURATION
+    log_on_failer  = HOST
+}