Need help decoding something with java:

[Taridge5188]

I know nothing about decoding or anything, my friend send me this thing and asked if I knew anyone who could help, it reads:

Today we'll be playing with AES, MD5 and SHA1. Solving this challenge rewards 2 keys.

Start with these keys partials:

Key 1: 8643-_120-_D_3-_893

Key 2: E5_D-_722-_2E8-6_85

Each gap is a missing uppercase letter from A to F. Find #1 and #2 so that

CIPHERTEXT = AES-CBC-128(data = 16 null bytes, key = first 16 chars of SHA1(#1), iv = MD5(#2))

HEX(CIPHERTEXT) == ce975cc4578f4a7005f22ad7182a4 d7640a00bd18c6f27c479cebfb1d1 778c8b

So #1 and #2 are the alpha keys you're looking for.


Not sure where to begin, can anyone help?

 

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[Taridge5188]

   

shhhh dont judge

[Ipquarx]

Considering I'm one of the resident cryptonerds I'll give it a shot.

[Becquerel]

Considering I'm one of the resident cryptonerds I'll give it a shot.

go ipquarx

[ThatRandomGuy]

Considering I'm one of the resident cryptonerds I'll give it a shot.

We're counting on you

[Taridge5188]

Considering I'm one of the resident cryptonerds I'll give it a shot.

go ipquarx

^^

I really appreciate it like you don't even know

[Ipquarx]

Assuming we're talking about hexadecimal characters for the key here and not ascii or whatever, the first 16 characters of SHA1(#1) is only 64 bits (Each hexadecimal character corresponds to 4 bits, 4 * 16 = 64 not 128), not 128 which the cipher requires. Can you confirm that he's intending it to be full characters?

[Taridge5188]

Assuming we're talking about hexadecimal characters for the key here and not ascii or whatever, the first 16 characters of SHA1(#1) is only 64 bits (Each hexadecimal character corresponds to 4 bits, 4 * 16 = 64 not 128), not 128 which the cipher requires. Can you confirm that he's intending it to be full characters?

If that means uppercase letters from A through F then yes

What I sent is (unfortunately) all the information it said and I'm technologically incompetent when it comes to this so I'm afraid I'm not much help

[Ipquarx]

Alright, I need one more piece of clarification before I get started. Should the hashes from this part: AES-CBC-128(data = 16 null bytes, key = first 16 chars of SHA1(#1), iv = MD5(#2)) be with uppercase or lowercase letters? Or can you not ask him?

[Ipquarx]

I'm sorry man, I tried, but I simply don't have enough specifics to be able to implement this properly. I implemented it with the best knowledge that I could get from the info but no combination seems to be working, I brute forced all 300 thousand combinations using different key/iv types too. Do you have ANY more info? is there even a remote chance you can milk a bit more technical info from your friend?