Cyber Quest CTF 2023 - Crypto

A crypto writeup from Cyber Quest CTF 2023 — a simple but time-consuming chain of base conversions and a rotation cipher to decode the flag.

Let's get Cracking...#

Challenge Description#

A person of age 64 gave coins to a boy of age 32 to buy 16 pens. Suddenly he dropped all 13 coins on the floor. He counted those coins 35 times.

Encrypted Text#

R1UyQ0FOREJFQTJUSUlCWE1JUURPTUJBR1kzQ0FORERFQTJXTUlCVkdJUURJT0pBR1UzQ0FOTEdFQTJUUUlCVUdZUURNTlJBR1UyU0FOTEdFQTNURUlCVEc0UURLWlJBR1JTU0FOUldFQTJEU0lCV0dJUURHTUpBR1EyU0FOWllFQTJXTUlCV01VUURFTUpBR1JSQ0FOSlpFQTJXTUlCVEhBUURPTVJBR1JRU0FOSldFQTNHQ0lCWE1RPT09PT09

R1UyQ0FOREJFQTJUSUlCWE1JUURPTUJBR1kzQ0FORERFQTJXTUlCVkdJUURJT0pBR1UzQ0FOTEdFQTJUUUlCVUdZUURNTlJBR1UyU0FOTEdFQTNURUlCVEc0UURLWlJBR1JTU0FOUldFQTJEU0lCV0dJUURHTUpBR1EyU0FOWllFQTJXTUlCV01VUURFTUpBR1JSQ0FOSlpFQTJXTUlCVEhBUURPTVJBR1JRU0FOSldFQTNHQ0lCWE1RPT09PT09

Solution#

Firstly I decoded the whole string using a base 64 decoder.

After that, I decrypted the respective string using the base 32 decoder.

After this, I converted the hexa-output into plain text.

Now I used the rotation cipher to fully decode the flag.

Flag: CSC{yoU_ARE_GOoD_a7_WoRk1Ng_w!TH_8aSEs}

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MUHAMMAD ABDULLAH