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When I submit an Customer Reference ID in an Android Application it POSTs an Encrypted String to an API Endpoint.

For example, if I enter the following CR ID :

"CR-13261150"

it POSTs the following Encrypted Data:

 splainText : "vpEz/Vm8Yi9v5/fzNE+MDoMIQGZ0vNvjPuX8UNAi26c="

      Count : 31

i can say count is based on Length of Customer ID,if the lenght is 11 then count is 31. (But All Valid Customer ID will have Length 11 for Sure)

Now let's assume if I submit the same CR ID in the following minute the Encrypted String Changes. But if I submit the same CR ID in the very same minute then for some reason I get the very same Encrypted String.

How do I find the encryption type and encryption method ?

I need help in decryption of the below encryption string.

And in my Last Question 2 People Answered Almost Correct,But Question was not clear to solve it Completly. please see this : How to Find Encryption Type by Seeing Encrypted Text?

Below Sample Data are Captured by Postman Proxy:

Input Text TimeStamp # Encrypted Text Count
CR-1 2022-04-05 02:17 0okiX0NBe8ebCMxtugOESY/UL9q20YVp8TQKEMQdpFU= 24
CR-12 2022-04-05 02:17 YfsK2i1KKN/2eWmTOs43Tm+hKK+fjN41Z3++Lq+s4q8= 25
CR-123 2022-04-05 02:17 oKDqXZ6LnLrfhQLzbxX9xRxsYZe5lxuMm79HAVm1fiQ= 26
CR-1234 2022-04-05 02:17 oj6mQ0dFnX3TsUfMbohfu/vc9vUAX+CIuj7kcVBqV4c= 27
CR-12345 2022-04-05 02:17 ksOZKdIif+su7zFoWIhpHqzlDWspUIiiUK2gyQ1rhPs= 28
CR-123456 2022-04-05 02:17 pZTWTBKIn5KwNS0xw+mkW1GyG1agA67GWoAiHgDNcjY= 29
CR-1234567 2022-04-05 02:17 cbnGD2N8e/rFo/2FebCfCOkThkTVLUyCpbw2YAIErAM= 30
CR-1234568 2022-04-05 02:17 dMniBANrtzK48iDPGeI59nRkOA47t7WUU73osxbtowA= 31
CR-13261150 2022-04-04 22:40 vpEz/Vm8Yi9v5/fzNE+MDoMIQGZ0vNvjPuX8UNAi26c= 31
CR-13261150 2022-04-04 22:42 vpEz/Vm8Yi9v5/fzNE+MDvJkkl9i6iF/gg++QsHKTfM= 31
CR-13261150 2022-04-04 22:43 vpEz/Vm8Yi9v5/fzNE+MDm1b+GWmC51UdhcUXD5Hjmw= 31
CR-13261150 2022-04-04 22:44 vpEz/Vm8Yi9v5/fzNE+MDsKjpyLB7YvaJhNqqhlCHmU= 31
CR-13261150 2022-04-04 22:45 vpEz/Vm8Yi9v5/fzNE+MDgNkvZYustpcpgQ0Aaj/dxc= 31
CR-18138469 2022-04-04 22:54 S5uLpQfVT8C4GRCoQTDL+1ENt2lNa7+Rra/gvAx97zQ= 31
CR-18138469 2022-04-04 22:55 S5uLpQfVT8C4GRCoQTDL+xuUFO0Si0cGYQL8WCo5Sxg= 31
CR-18138469 2022-04-04 22:56 S5uLpQfVT8C4GRCoQTDL+y6puq8h6V0N326T/BMr+p4= 31
CR-18138469 2022-04-04 23:01 S5uLpQfVT8C4GRCoQTDL+/nZFmv3EYRdC8iG66mfgD8= 31
CR-26752464 2022-04-04 23:05 fT7K9VSRWTTYCYF51PJA02GfRjfRY8c4K1V5CptfHCs= 31
CR-26752464 2022-04-04 23:06 fT7K9VSRWTTYCYF51PJA024r3eotFDInICu99mzuuqI= 31
CR-26752464 2022-04-04 23:07 fT7K9VSRWTTYCYF51PJA07SxLQrsVZGNNgF+Dv4f/Pg= 31
CR-22224896 2022-04-04 23:10 8slKBTMUBaSap9VrwL3YZ/WgR9hqauqTkg9RmKVeHCI= 31
CR-22224896 2022-04-04 23:11 8slKBTMUBaSap9VrwL3YZw/dAhQtMzpsas1T5A8SJiU= 31

enter image description here

Cruzer Blade
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1 Answers1

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What you're describing is known as a "Chosen Plaintext Attack (CPA)", which wikipedia describes as:

A chosen-plaintext attack (CPA) is an attack model for cryptanalysis which presumes that the attacker can obtain the ciphertexts for arbitrary plaintexts.1 The goal of the attack is to gain information that reduces the security of the encryption scheme.[2]

Modern ciphers aim to provide semantic security, also known as ciphertext indistinguishability under chosen-plaintext attack, and they are therefore, by design, generally immune to chosen-plaintext attacks if correctly implemented.

So if they are using a strong cipher, then no matter how many Input Text : Encryption Text pairs you have, you should still not be able to learn anything about the cipher used.

Your best bet is probably to reverse-engineer the Android binary and try to study the algorithm directly.

Mike Ounsworth
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