Cryptography (easy) challenge
Hello, I have to do a simple cryptography challenge for school. You'll find the file and the context (fr and en) below. I figured out that it is encoded as base64. When decoded it's a gzip, which contains a .bmp which got xor encrypted. I need help to find this key. I have no hints about it
https://tinyurl.com/needurhelpp
Quelques minutes avant le crash de l'hélicoptère du GIC, le système d'imagerie satellitaire d'Osland a réussi à capturer une image de l'engin en perdition.
Malheureusement, les multiples cyber-attaques à l'encontre des systèmes d'Osland ont pour effet d'entraîner des dysfonctionnements matériels des stations de surveillance satellitaire, et les images transmises par ces dernières sont chiffrées par l'intermédiaire de clés erronées.
En effet, les stations transmettent des images au format BMP, chiffrées à l'aide de Xor, et compressées par Gzip.
Afin d'identifier une potentielle zone de crash de l'hélicoptère, il est essentiel de récupérer l'image transmise.
L'image est accessible ici
Le flag est au format FLAG{}
A few minutes before the GIC helicopter crashed, Osland's satellite imaging system managed to capture an image of the sinking craft. Unfortunately, multiple cyber attacks on Osland's systems are causing hardware malfunctions at satellite monitoring stations, and images transmitted from them are encrypted using incorrect keys. Indeed, the stations transmit images in BMP format, encrypted using Xor, and compressed by Gzip. In order to identify a potential helicopter crash zone, it is essential to recover the transmitted image. The image is accessible here The flag is in FLAG{} format
9 Replies
some tips to get you started. after base64 decoding and decompression, you have 1048714 bytes of encrypted data. since you know it's bmp, the first six bytes are known to be BM (two bytes) followed by four bytes that is the length in bytes of the file, encoded as little endian.
xor data: 0x07, 0x3f, 0xb8, 0x46, 0x51, 0x52
header: (byte)'B', (byte)'M', 0x8A, 0x00, 0x10, 0x00
start of key: 0x45, 0x72, 0x32, 0x46, 0x41, 0x52
Unknown User•2w ago
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so if I'm right, Sehra 'choosed' a way to find the encryption key and you, tebeco, a way to get informations about the image without decoding it ?
bloqué sur le mm challenge, passe mp on a peut etre des infos a s'echanger
Unknown User•2w ago
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i was just saying that i am in the same case
Any clue about the decoding here ??
still nothing for me, wbu ?
None, still searching !