[Sharif University CTF 2016] [Reverse 50 – dMd] Write UpFlag is : The valid input
The file is a: dMd: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=2643fecd383362fe9593ef8605a9ce882a85a38a, not stripped
Continue reading [Sharif University CTF 2016] [Reverse 50 – dMd] Write Up
[Sharif University CTF 2016] [Misc 300 – Sec-Coding 2] Write UpYou should fix vulnerabilities of the given source code, WITHOUT changing its normal behaviour.
Rules & Notes
MISSION: You should fix vulnerabilities of the given source code, WITHOUT changing its normal behaviour.
RULE0: When an honest user gives a non-malicious (but maybe incorrect) input which does not trigger the vulnerabilities,
the output of uploaded fixed code should be the same as before.
RULE1: When the attacker gives his/her attack vector, your program should not crash or do dangerous actions (explained below),
but continue its execution and exit normally at the end. In this situation, your program is allowed to output anything.
RULE2: A (poorly-tested) source code may crash even when interacting with a normal user. You should fix these cases too.
(NOTE: the output should be correct in this case)
Dangerous actions (stated above) includes buffer overflows, writing to unallocated memory address, reading uninitialized memory,
and any other programming mistakes leading to crash/instability.
Some prevention techniques, detect the attack and prevent memory corruption but throw an exception which terminates the program,
leading to denial of service. You should avoid such termination and the program should recover from the attack, continue execution,
and exit normally at the end.
Continue reading [Sharif University CTF 2016] [Misc 300 – Sec-Coding 2] Write Up
[Sharif University CTF 2016] [Misc 100 – Sec-Coding 1] Write UpYou should fix vulnerabilities of the given source code, WITHOUT changing its normal behaviour.
Rules & Notes
MISSION: You should fix vulnerabilities of the given source code, WITHOUT changing its normal behaviour.
RULE0: When an honest user gives a non-malicious (but maybe incorrect) input which does not trigger the vulnerabilities,
the output of uploaded fixed code should be the same as before.
RULE1: When the attacker gives his/her attack vector, your program should not crash or do dangerous actions (explained below),
but continue its execution and exit normally at the end. In this situation, your program is allowed to output anything.
RULE2: A (poorly-tested) source code may crash even when interacting with a normal user. You should fix these cases too.
(NOTE: the output should be correct in this case)
Dangerous actions (stated above) includes buffer overflows, writing to unallocated memory address, reading uninitialized memory,
and any other programming mistakes leading to crash/instability.
Some prevention techniques, detect the attack and prevent memory corruption but throw an exception which terminates the program,
leading to denial of service. You should avoid such termination and the program should recover from the attack, continue execution,
and exit normally at the end.
Continue reading [Sharif University CTF 2016] [Misc 100 – Sec-Coding 1] Write Up
[Sharif University CTF 2016] [Crypto 100 – Universal re-encryption] Write UpUniversal Re-Encryption
Let p be a prime, and g be an element of ℤ/pℤ of prime order q.
Let x ∈ ℤ/qℤ be the private key, and h = g^x (mod p) be the public key.To encrypt a message m ∈ ℤ/pℤ, pick two random values r, s ∈ ℤ/qℤ, and compute the ciphertext as follows:
(a, b, c, d) = (g^r, h^r, g^s, mh^s).Download a valid ciphertext σ = (a, b, c, d) below, and compute another valid ciphertext σ′ = (a′, b′, c′, d′) such that:
σ and σ′ decrypt to the same message;
a ≠ a′ and b ≠ b′ and c ≠ c′ and d ≠ d′.
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[Sharif University CTF 2016] [Crypto 50 – Rail Fence Cipher] Write UpDecrypt and find the flag.
Ciphertext is: AaY–rpyfneJBeaaX0n-,ZZcs-uXeeSVJ-sh2tioaZ}slrg,-ciE-anfGt.-eCIyss-TzprttFliora{GcouhQIadctm0ltt-FYluuezTyorZ-
Continue reading [Sharif University CTF 2016] [Crypto 50 – Rail Fence Cipher] Write Up
